Habitable conditions on Venus may not be entirely impossible, however. Although its surface would be unable to support life as we know it, the upper atmosphere of Venus, about 50 km above the surface has Earth-like temperatures and could host extremophilic organisms. As humans and our technological creations move out into space, Venus may also serve as a subject of terraformation. Venus may once again become an Earth-like world with oceans if it is successfully terraformed. Like with Mars though, confirming the existence or non-existence of life in Venus’s clouds may be ethically required before any terraformation attempt can be made. Otherwise, maybe Earth is the evil twin after all.

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Introduction

Venus is simultaneously one of the most Earth-like and one of the most alien planets in our solar system. It is comparable to Earth in terms of its size (diameter ~ 12,100 km) and has geologic regions that appear to be analogous to the cores of continents on Earth. On the other hand, Venus is also incredibly alien. It has extreme surface temperatures (~500 C or ~900 F) and a surface atmospheric pressure of 93 bar, or 93 times Earth atmospheric pressure at the surface, comparable to the pressure 1 km or half a mile deep in Earth’s oceans. Understandable, Venus is generally considered profoundly inhospitable to life on Earth.

Because of the very bleak prospects of Venus’s habitability, the planet Venus has been ignored relative to her brother planet Mars for the last 30 years. This began to change in 2020, however, when a paper came out suggesting the presence of phosphine in Venus’s upper atmosphere. Phosphine is an organic compound that is found either in the atmospheres of the giant planets or in penguin guano on Earth. Confirmation of phosphine in the clouds of Venus would definitely be a very compelling indication of life in Venus’s atmosphere since it is not clear what geological process would produce it on Venus.

The presence of phosphine is highly contested and probably will continue to be until we send another spacecraft to Earth’s evil twin. The more significant outcome of the discovery is a revived interest in the planet Venus, as two missions are planned, VERITAS and DAVINCI to explore Venus, the first NASA missions to Venus since the Magellan mission ended in 1994.

There is also another reason Venus has become more significant. Earth sized exoplanets are of significant interest because of their potential to be Earth-like. Earth-sized, however, still does not mean Earth-like since Venus is also roughly Earth-sized and definitely not Earth-like. We still do not know enough about planetary processes to know which is the weird case. Do most Earth-sized planets end up like Earth while a few become like Venus or is Venus the typical case? Understanding what happened to Venus may also help us to predict whether exo-Earths or exo-Venuses are more common in the universe.

Geological Timescale of Venus

One way that Venus is more like Earth is that most of its geology is young, whereas the other terrestrial planets (Mars and Mercury) and the Moon all have mostly geologically ancient surfaces dating back 3-4 billion years in some cases. The current surface of Venus is estimated to only be 300-800 million years old based on crater counts, which assume that craters will accumulate over time on surfaces without an erasing mechanism so that surfaces with more craters are generally older than surfaces with fewer craters. There are differences of opinion on how to frame the geologic timescale of Venus, but a generally well-supported version of the Venusian timescale is one divided into four periods, the pre-Fortunian, Fortunian, Guineverian, and Atlian.

The Pre-Fortunian represents the period of Venus’s history before the catastrophic resurfacing event that made Venus into a sort of hell. No current geology on Venus likely survives from that time. The Fortunian period is characterized by intense tectonic activity creating large plateaus that have been compared to Earth continents. The Guineverian is a period of excessive volcanic eruptions where large volcanic plains were created by hardening lava flows. The cratered plains later cooled and resulting in wrinkle-ridges. The Atlian period is defined by a mixture of volcanic and tectonic resurfacing and the emergence of the present-day state of Venus.

Pre-Fortunian

For 80-90% of its history, Venus may have been a very different planet. Studies of deuterium/hydrogen ratio within the atmosphere of Venus show that the planet has lost significant amounts of water over the course of its history, enough water to warrant an ocean. We will not really know until we send a spacecraft to collect more data, but Venus may have been an Earth-like world with oceans and least disconnected seas for most of its history.

The cataclysm

Although it is debated, some think that Venus ha always been the way it is and that there was no cataclysm, a common hypothesis is that Venus experienced as catastrophic event about 800 million to 1 billion years ago which involved a runaway greenhouse effect and to the overturning of the crust. Crater counts of the surface of Venus suggest that the current crust of Venus is less than 1 billion years old and that the pre-catastrophe geology has not survived. If there was a catastrophe, it is not clear what caused the event. One possibility is the emplacement of a large igneous province or flood basalt led to the release of enough carbon dioxide and other greenhouse gases that triggered the runaway greenhouse effect and evaporation of any primordial ocean. While speculative, the evaporation of a primordial ocean may have shut down or significantly slowed any pre-existing plate tectonics, which would have meant that greenhouse gases could not be recycled the way that are on Earth but would continue to build up in the atmosphere. This could easily make a hypothetical ancient Earth-like Venus into modern Venus.

Fortunian Period

Venus after the cataclysm

As far as planetary scientists can tell, no geology from the pre-Fortunian survives to the present-day. Although it is possible that geologic fragments like rocks and minerals have been preserved in later rock layers. The oldest identifiable units of Venus are rugged highlands called tessarae (singular = tessera). The Fortunian period gets its name from Fortuna Tessera, one of the major highland regions. The tessarae probably formed through series compression and extension similar to how mountains form on Earth when two continental plates collide leaving to the crust in the middle becoming folded or wrinkled. Unlike mountain building on Earth though, The tessarae of Venus did not involve the collision of tectonic plates, but rather a single planet-wide plate that was in tension in some areas and under compression in other areas, possibly driven by convective processes within Venus’s mantle. The tesserae may be the Venusian analogue to the low density crust that makes up the cores of Earth’s continents. This period probably only lasted about 100 million years based on crater counts and stratigraphic relations to the rest of Venus.

Guineverian Period

The period of tessera formation was followed by a long period of volcanic eruptions. During this period, named for the volcanic plain, Guinevere Planitia, vast lava flows filled the low lands between the tesserae. These lava lakes hardened into volcanic plains. Over time as these plains cooled, the rock contracted forming wrinkle ridges. The Guineverian period lasted perhaps 200 million years (very roughly based on crater counts). It is not clear what led to this transition from tectonic deformation being dominant to volcanism being dominant. One possibility is the role of rifting. If there was a period where Venus was a lava world of seas of molten rock (perhaps other than right after the catastrophe), it would have been this period.

Atlian Period

The volcanism-dominant Guiniverian was succeeded by the Atlian period, named for the shield-volcano studded plain Atla Regio. The Atlian represents perhaps the last 500 million years of the history of Venus and is characterized by both volcanic activity and tectonic activity. It is during this period that some of the most interest feature on Venus likely formed. These features include large shield volcanoes which led to the formation of new lava flows that lack the wrinkle ridges of the earlier Guiniverian plains.

Another feature associated with this geologic time period are the Venusian coronae. The coronae (singular = corona) are roughly circular concentric regions about 200 km across. The only other planetary body with features comparable to the coronae on Venus is Uranus’s icy moon Miranda.

The transition from a volcanism-dominant regime to a mixed regime of volcanic and tectonic processes during the Atlian and suggests an increasing geological complexity, and geodiversity, on Venus over time. If compared to the evolution of biological complexity, and biodiversity, the catastrophe at the end of pre-Fortunian time could be considered a geological mass extinction event. The increase in the diversity of tectonic and volcanic features could represent a gradual restoration of an original complexity over time. This is analogous to the gradual restoration of biodiversity as new organisms and ecosystems evolve and new species fill empty niches in the aftermath of a mass extinction event. Geological and biological complexity also may not be completely unrelated. Coincidentally, coronae have been suggested to be evidence of a more Earth-like plate tectonics on a regional scale on Venus. Could an Earth-like system of plate tectonics be emerging on Venus? Could it be a restoration of something that previously existed before the pre-Fortunian catastrophe?

This is pure speculation, but if Earth-like plate tectonics (meaning where rock is being recycled at subductions zones between separate tectonic plates) is being slowly re-established on Venus, this may present hope for the future of the habitability of Venus. It was largely plate tectonics on Earth that allowed for the development of stable temperature regimes and biogeochemical cycles that could allow for the flourishing on life on Earth. Perhaps in another 500 million years, Venus could be Earth-like again. One challenge to this is the fact that Venus has entirely lost its water and it was probably the presence of water oceans that enabled plate tectonics by lubricating the rock on Earth. Kick-starting plate tectonics on Venus may therefore require some sort of intervention.

Life on Venus?

Current life (as we know it at least) on Venus at the surface is unlikely given its extremely hostile conditions. One the other hand, the increasing geological complexity of Venus and also the possibility of a re-ignition of Earth-like plate tectonics does at least make it plausible that the emergence of biosphere could exist in Venus’s future even without human intervention.

Such life on Venus, however, re-emergence of Earth-like plate tectonics and re-introduction of large volumes of water notwithstanding, is still unlikely to be Earth-like life and will more likely be some sort of weird-life, such as silicon-based life.

Astrobiology researchers, such as Sarah Johnson at Georgetown University, have made a case for agnostic biosignatures based on the premise that life may be something that might emerges out of any complex chemistry or chemical disequilibrium and not just carbon-based chemistry. Increasing complexity in Venus’s geology could also mean increasing complexity in its geochemistry, which may lead to a form of life even if it is not as we know it.

What about the atmosphere?

A present day biosphere on Venus is very unlikely but if there is life on Venus in the present epoch, it would have to be in the upper atmosphere. About Fifty kilometers or thirty miles above the torrid ~500 °C (~900 °F) surface is a region that is about 60 °C (140 °F) and the atmospheric pressure is only 1 atm, same as at sea level on Earth. While still hotter than Earth’s hottest deserts and in an atmospheric zone containing significant levels of sulfuric acid, conditions in Venus’s upper atmosphere at 50 km attitude are still drastically more favorable to life compared to Venus’s surface since organisms on Earth are known to live in comparable temperature and PH conditions. Earth has an aerobiosphere made up of microbes that live at high altitudes in the atmosphere. Could remnants of a Venusian aerobiosphere from the pre-Fortunian have survived surface paroxysms in the upper reaches of the atmosphere?

Venus in the Anthropocene

On March 1, 1966, a space object crashed onto the surface of Venus. This object was the Soviet Venera 3 lander. The intention of the object was to extend the awareness of the Earth system to the planet Venus. The first space probe to successfully land on Venus and return was the Venera 4 lander which made touchdown over year later on October 18, 1967.

Although the probe didn’t last long on the surface (only 93 minutes), this represents the beginning of the Anthropocene on Venus. However tenuously, humans had now entered picture through their robot avatars and had in some way changed the chemistry of Venus. The unfolding the of the Anthropocene in the solar system has been slow, however, and is likely to be even slower on Venus because of its harsh conditions.

Unlike Mars, which was mostly visited by U.S. spacecraft until fairly recently with Indian and Chinese spacecraft joining NASA on the red planet, Venus was mostly explored in the 20th century by the Soviet Union. As the Moon and Mars are about to be absorbed by space capitalism, Venus remains stubbornly communist with only Soviet hardware actually having reached the surface. Perhaps the same way that communist countries in the cold war considered themselves to be resisting American imperialism, Venus is joining the revolution and resisting Earth bio-imperialism by destroying the spaceships of alien invaders with its corrosive atmosphere and surface conditions.

Speaking of Earth bio-imperialism—Terraforming Venus?

Terraforming Venus may seem far fetched, but Venus may be more promising as a terraformation target than Mars. It is easier to take away atmosphere than add atmosphere. Where as Mars’s atmosphere is too thin, Venus’s atmosphere is too thick. Furthermore, Venus is closer to Earth in size, meaning that it may be overall easier to establish Earth-like conditions on Venus with its comparable gravity. One Early suggestion for terraforming Venus included using sunshades to block out the sun so that the atmosphere freezes to the ground. In this scenario, once the atmosphere had been frozen out as dry ice, it would be buried leaving only the CO2 needed to reproduce an Earth-like atmospheric pressure. Water and oxygen would also still need to be added in this scenario.

If terraformation of Venus actually happens, it is likely to be less dramatic and brute force. For example, microbes could be used to process the atmosphere to reduce sulfuric acid and carbon dioxide and increase atmospheric oxygen. This was suggested in an early paper by Carl Sagan. Furthermore, there isn’t a need to settle the surface. We could just live in sky cities like Cloud City on the fictional planet Bespin from Star Wars.

Before terraforming Venus, however, the most significant issue might be the ethical one. While it is unlikely that there is life in the clouds of Venus, the discovery of life there could mean that terraforming Venus would require us wiping out a native biosphere. Is it our place to decide which biosphere continues and which one does not? Like with Mars, it could be argued that in that case Venus belongs to the Venusians. Terraforming Venus may end up being the right decision, but we must take into account planetary protection and confirm whether there is indigenous life on Venus if we want to be more than just Earth bio-imperialists. Otherwise, maybe Earth is the evil twin after all.

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Recently, I had two conversations about the role of planetary science in the future of space development. In one conversation, my friend had been in planetary science but with advances in artificial intelligence now wondered whether we should focus on AI for now and AI could explore the universe later on our behalf. In another conversation, where we were talking about the importance of seeing intrinsic value in the space environment as space entrepreneurs make plans to mine the moon and asteroids, another friend asked why space conservation should be a focus. He was much more concerned about the threat of super-intelligent AI wiping out humanity.

In the 2014 book Superintelligence: Paths, Dangers, Strategies, the philosopher Nick Bostrom outlined a scenario where an AI programmed to make paperclips becomes so focused on its single task that it makes the entire universe into paperclips. This is a common example of an artificial super-intelligence choosing an arbitrary task that harms humanity that cannot be stopped. This scenario seems less like science fiction to experts in AI research now than it did in 2014 due to developments such as the Mythos incident and the recent release of Claude Fable earlier this year (2026).

What is striking about the paperclip example is that is highlights the reason that planetary science and similar endeavors are essential to deterring the development of dangerous or non-aligned AI. Seeing the universe as being a marvel worth exploring encourages us to see the natural world as intrinsically valuable and thus more likely to create AI models that have the same attitude.

The scientific revolution was good in many ways. In addition to giving us a better understanding of the cosmos and our place within it, modern science has enabled us to heal previously incurable diseases, reduce famine, and create unprecedented levels of material prosperity. On the other hand, an 18th-19th century reductionist materialism led to the natural world primarily being seen either as an inanimate object to be dissected or as an economic resource to be exploited.

A result of this development is that there is a tendency in Western thought and now more broadly our currently global civilization to see nature as a blank canvass or warehouse of resources for humans to shape the universe as they see fit. Arguably, the environmental crisis of the mid-20th century and the ongoing climate crisis has challenged that view. Modern science now has a better understanding of Earth as being fragile and interconnected and that it is possible for our civilization to change the Earth in ways that are potentially harmful.

Interestingly enough, space exploration played an indirect role in this since it was viewing Earth from the moon for the first time during the Apollo 8 mission on December 24, 1968 that drove home the point of Earth’s fragility and uniqueness. For the first time, humanity saw Earth in true perspective and grasped that planet is finite and vulnerable in a vast unforgiving cosmos. The image of Earth above the Lunar surface helped inspire the environmental movement. Fifty-eight years later, a similar image was taken from the Artemis II spacecraft on April 6, 2026.

Carl Sagan’s celebration of the “pale blue dot” also has been a source of inspiration for valuing the planet we call home. The idea of Earth as being intrinsically valuable, fragile, and more than just a source of raw materials was extended to the outer space environment itself early in the Space Age. This is reflected even before the Earthrise image in the Outer Space Treaty (1967), which forbids activities that would harmfully contaminate the outer space environment or Earth itself (Article IX).

The pre-eminent advocate of human space exploration Carl Sagan also interestingly was critical of space development efforts that did not regard the integrity of the space environment. In his book Pale Blue Dot, inspired by image of the same name, Carl Sagan specifically criticized more extreme approaches to terraformation (like blasting away the whole atmosphere of Venus or nuking the ice caps on Mars) as being too brute force and disruptive to a planetary surface environment and its unique geology and characteristics. In the same book, Sagan also said that if there is life on Mars that we should not settle Mars. Mars would belong to the Martians.

In contrast, more recent space advocates don’t always seem to appreciate the intrinsic value of the space environment. Elon Musk is certainly interested in making Mars a future home for human civilization but has said very little about the value of Mars apart from its potential as a colony. Dr. Robert Zubrin of the Mars society has ridiculed the idea that we should avoid contaminating Mars with invasive Earth species even though astrobiologists consider this to be a major concern for both verifying that genuinely extraterrestrial life has been found and to avoid causing a mass extinction of a native ET ecosystem before we can discover it.

How does this relate to AI? If we just see the universe as warehouse of raw materials or as a passive stage for human history to play out, what is to stop us from creating an AI with the same attitude that ends up doing the very kind of thing that the AI in Nick Bostrom’s thought experiment does? After all, it could be argued that humans are already acting like paperclip generators as we cut down primeval rainforests to mine critical minerals for electronics essentially transforming rainforests into smartphones. I am not against technological development or mining, but if we don’t believe that at least some rainforests shouldn’t become smartphones, what is to stop us from building an AI with the same attitude? Also, if an AI only sees the universe as a source of raw materials, what is to stop them from seeing humans that way as well eventually (while technically aliens, this is the plot of All Tomorrows by C.M. Kösemen)?

While not the solution by itself, inspiring wonder through planetary exploration can be a form of cognitive security because it deters us from both becoming paperclip maximizers ourselves and from creating AI with the same attitude. Conversely, if we intrinsically value the space environment as well as Earth’s environment, it is more likely that we will create an AI that values the natural environment (and humans) as well.

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It has long been known that natural terrain and artificial structures differ in their fractal index. Buildings tend to be more euclidean whereas natural features tend to have a fractal curve to them. This potentially gives artificial structures a fractal signature which could be used as a proxy for the level of computation on a planetary surface since urban centers are associated with higher levels of computation. To test this, I created an anomaly detection model to identify features of unexpected fractal index, for natural terrain, and tested it on two Earth cities. The results of this preliminary study suggest that high fractal index and high spectral periodicity (how often certain shapes re-occur) may be useful indications of artificiality indicating agricultural or urban terrain as opposed to forest terrain that tends to have low fractal index and low spectral periodicity. Orientation entropy is taken to be an ambiguous signal since it varies considerably across agricultural and urban terrain. This study suggests that the computational complexity of a planetary system could be read off its surface like circuits can be read off a microchip.

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Introduction

Nature is fractal. What this means is that nature contains many repeating patterns that appear the same regardless of scale. This is illustrated by a natural coastline. Whether you view a coastline at 100 m/pixel resolution or 10 km/pixel resolution, the natural coastline will look the same in having the same types of gentle curves. Artificial structures often stand out in having sharp regular edges appearing more euclidean. Unlike the fractal nature of the coastlines, these patterns do not always repeat with increasing scale. This is not to say that cities are not fractal, but they have a fractal signature that differs noticeably from natural terrain.

This is important for the search for technosignatures, that is, indications of technology, in the solar system and beyond. It also means that a spacecraft orbiting an planet or exoplanet could in theory detect terrain that is artificial in origin by identifying terrain that is anomalous in its fractal index compared to the expected fractal index of natural terrain. Assuming that more advanced civilizations rework larger areas of their planet’s surface, the fractal index across a planetary surface could also be considered a proxy for how advanced a planetary civilization is and thus the level of planetary computation, that is, how much information is being processed by a planetary system at a given time.

It can be assumed that more advanced civilizations will mean higher levels of computation. For example Ancient Egyptians were just as smart as modern engineers in New York City, but the level of computation being done in modern New York with computers and AI is likely much greater than the computation being done by ancient Egyptians who only had papyrus, brains, and a smaller population.

Methodology

I constructed a variational autoencoder (VAE)-based anomaly detection model trained on natural terrain (forests, hills, etc.), so that it will flag terrain that does not have the geometry and texture of natural terrain as anomalous. For this study, I chose sample two satellite images. One image is of Grand Forks, North Dakota, a city in the North American Great Plains surrounded by farmland. Grand Forks is also the location of the University of North Dakota, where I did my PhD.

The other image is of Manaus, Brazil, a city surrounded by the Amazon rainforest and a large river, the Rio Negro. Grand Forks allows for comparison two types of engineered terrain (urban vs. agriculture). Manaus allows for comparison between engineered terrain and natural terrain (urban v.s. rainforest canopy). For each image, I ran the model to evaluate the fractal index of the urban and agricultural terrain compared to natural terrain (rain forest and rivers).

In addition to fractal index, which deals with texture and how it changes with increasing scale, I included orientation entropy, spectral periodicity, and reconstruction error as model weights.

Orientation entropy is the degree to which edges in an image follow specific directions. A random distribution of edge orientations would result in high entropy whereas a very regular distribution of edge orientations would result in low entropy.

Spectral periodicity involves how often specific patterns occur. Terrain where the same types of shapes occur repeatedly would have high spectral periodicity. Terrain where the shapes vary considerably over space would result in low spectral periodicity.

Finally, reconstruction error is the degree to which terrain differed from what is assumed to be the natural terrain in terms of fractal index, but also orientation entropy and spectral periodicity. These weights were used in calculating the overall anomaly score for terrain, determining how much the terrain differs from what is expected of natural terrain.

Results

For the Grand Forks image, the model revealed that the fractal index (D) was higher for the city (D = 2.55) than the surrounding farmland (D = 2.3-2.4). The surrounding farmland had a lower orientation entropy, suggesting that the country roads are at more predictable orientations (e.g., N-S and E-W) than the city streets. The spectral periodicity was higher for the agricultural land, suggesting that the rectangular plots are more regular than the irregularly shaped buildings and urban lots. Curiously, the anomaly score is higher for the farmland, suggesting that agriculture could also be a strong geometric indicator of artificiality and not just urban centers.

For the Manaus example, the feature with the highest fractal index was the the urban center and the Rio Negro river, suggesting that high fractal index can also indicate specific natural features. The city also showed a high orientation entropy with the lowest orientation entropy being shown by the Rio Negro. In contrast to agricultural land, the natural forest showed low spectral periodicity and low fractal indext, suggesting spectral periodicity and fractal index is may be a reasonable indicator of artificially worked terrain.

Overall, the artificial terrain, the urban centers and the agricultural terrain were characterized by a high fractal index and high spectral periodicity. Orientation entropy is an ambiguous signal since it was high in the urban centers but low in the agricultural centers. These preliminary results provide a guide for principles that could be used to identify artificial terrain on other planets based on texture and geometric patterns.

Current exoplanets are too far away for this kind of analysis and it is unlikely that such analysis is going to reveal evidence of a lost civilization on Mars or the Moon. Nonetheless, analysis of how geometric and texture patterns on planetary surfaces differ between natural and artificial terrain may one day enable probes to identify landscape-scale planetary technosignatures on Earth-like planets.

This is a preliminary study and a follow up study would confirm that the characteristics associated with artificiality would be common across terrain types (for example, would the same principle apply to desert terrain relevant to Mars?). Nonetheless, this preliminary study does suggest the usefulness of this approach. Planetary computation may be written into a landscape the way computation is etched into microchips. We just have to know how to recognize it.

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For example, civilizations and intelligence can be thought of as emerging out of planetary systems. In this paradigm, intelligence doesn’t just happen on a planet. It happens to a planet. One way to think of planetary intelligence is to consider it as computation by analogy to AI systems. Life may not form on all planets, but where life does take over a planet, a planetary stack may evolve with technological and biological layers. Technosignatures (indications or evidence of technology) are essentially signatures of the postbiological planetary stack and how it evolves over time. Technosignatures measure the development of the planetary stack.

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The solar system has a large range of planets, from worlds that have changed little in billions of years, such as the planet Mercury, to planets which are constantly changing due to their geology and atmosphere, such as Earth itself. In fact, Earth may be the most dynamic planet in the solar system with its hundreds of active volcanoes, active plate tectonics, weather, and of course the mysterious phenomena of life and intelligence. Earth is not just dynamic, but has also evolved numerous layers including a biosphere, all living things, and now a technosphere, the technosystems that cover the planet (e.g., cities). Artificial intelligence could be considered the latest layer of planetary intelligence. The question you might ask relevant to planetary exploration whether this has happened to other planets. Could other planets have become developed stacks to drive planet-wide computation?

Intelligence could be considered a planetary process if defined as the information processing within a system. In nature, most information is processed very slowly, think of how long it takes an ecosystem to respond to a change like the introduction of a new species. Through induring mass extinctions and events like asteroid impacts and returning to a stable equilibrium, Earth’s biosphere can be seen slowly taking in information over time and responding to it, so it could be argued that there is a distributed low level planetary intelligence. The processing of information is most efficient and dense, for the moment, within the human brain.

Human intelligence emerged the intelligence of primates and it appears that artificial intelligence is growing out of human intelligence. Could this lead to the emergence of a higher planetary intelligence? For example, satellite networks have allowed humanity to see itself from space and observe what is happening to the Earth system and respond to threats ranging from natural disasters to climate change. Could this not be an example of the planet itself becoming intelligent through collective human intelligence? Perhaps, humans are the layer through which the planet comes to know itself.

We only have a sample of n = 1, so it is not clear that all civilizations advance in the same way as humanity, but a generalized understanding of what is happening as humans spread across the planet could be the emergence of a new planetary intelligence where intelligence is acting as a geologic process re-shaping metal, carbon, and silicon into cities, computers, and ultimately infrastructure to support agents in the cloud.

This complexity has also spread to other planets as humans have sent probes to observe other planets and even land on their surfaces, but this explosion of intelligence remains concentrated on Earth. Mars and the Moon are still yet to become planetary intelligences themselves. Even with all the orbiters at Mars, it is still more correct to say that Mars’s satellite array is a way that Earth observes Mars, not a way that Mars observes itself. The complexity of Earth’s interconnected systems stands in contrast to the relatively inert, geologically dead terrestrial worlds of the solar system, such as Mars, Venus, Earth’s Moon, Mercury, and the icy moons of the outer planets.

An exception to this is Jupiter’s moon Io with more active volcanoes than Earth, tectonic mountain ranges (most planetary bodies other than Earth are not geologically active enough for mountains to form this way), and a surface that is constantly churning.

Life on Io would not be life as we know it, but if life is the result of complex chemistry, I would not be surprised if we did find some sort of weird life on Io which could evolve a form of weird computational intelligence, weird from our perspective anyways.

Of course, since we only have a sample of n = 1, we cannot know for certain how this planetary stack evolves and emerges. This is where the tools of SETI could help to answer the question of how this stack evolves.

How would we detect emergent complexity or planetary computation over interstellar distances? Commonly cited ways include the detection of industrial pollutants in exoplanetary atmospheres, which would indicate the activity of a civilization, such as CFCs. Another example is the search for alien megastructures, such a Dyson spheres, a hypothetical construct built to enclose entire an star and capture its energy. There is also the familiar approach of listening for alien radio signals.

Two recent papers suggest it might even be possible to map compute distribution on a planetary and even sub-planetary scale across interstellar distances. In one recent paper, the author develops a model that uses Doppler drift of radio signal due to planetary rotation to create a crude map of the distribution of signal across Earth (modeled as if an exoplanet) which could be used to roughly map population centers on an exoplanet using signal strength as a proxy for population size.

Another paper uses a similar approach where specular reflection is used to map the surface of Earth observed as an exoplanet to demonstrate that specular reflection can potentially be used to detect subplanetary scale structures (e.g., cities built of glass and steel) on a planetary surface and create a crude map of the distribution of urban centers on an exoplanet. Although still new and yet to be applied to actual exoplanet data, these approaches are promising. They have the potential to not only determine whether or not planetary computation is happening but actually provide clues to the distribution and possible development of compute across a planetary surface.

Planetary computation is a speculative concept, but it can be useful in making predictions about the development of other civilizations and how they might be detectable. It also has implications for our own civilization. If other centers of planetary computation have survived long enough to be detectable by our current methods, it shows that there may be a future for our own planetary stack.

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This makes asteroid impacts a significant threat to humanity that is also neglected. Addressing this threat would allow humanity to build a planetary defense system to prevent the destruction of human civilization or Earth’s biosphere. It would also eventually allow us to intercept asteroids for other reasons, such as resource utilization and creating potential future habitats for humanity and other Earth life. In this way, addressing planetary defense, both protects life on Earth, the only living planet we know of at the moment, and enables us to potentially spread Earth life and intelligence beyond our home planet into the cosmos.

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In 2013, an incoming ~20-meter (65-foot) asteroid exploded in the atmosphere above the town of Chelyabinsk, Russia, resulting in shattered windows and a few people being knocked off their feet, but relatively little real damage. If the asteroid had instead reached the surface, however, Chelyabinsk wouldn’t exist anymore. Chelyabinsk is a recent example of the real danger of impacts by large asteroids and comets. Other examples include the Tunguska event of 1908, where a comet likely exploded over a forest in Siberia, flattening the trees for miles. There is also of course the ~10 km asteroid that created Chixculub crater in the Yucatan peninsula that led to the extinction of the dinosaurs 66 million years ago.

Asteroid or comet impacts represent low probability, high impact (no pun intended) events. They may not happen very often but when they do, large asteroids could destroy a city, a country, or even wipe out all life on Earth depending on their size. For this reason, asteroid strikes represent a real threat to human civilization that should be considered alongside other threats like climate change or non-aligned artificial intelligence. The good news is that asteroid impacts are also 100% preventable if we can detect the incoming asteroid in time.

Despite the demonstrated risk of asteroids strikes and the fact that they are preventable unlike other natural disasters, like volcanic eruptions or earthquakes, planetary defense has received little attention or funding. For example, there has so far only been one spacecraft mission dedicated specifically to planetary defense (the DART mission in 2021-2022). The first telescope launched specifically to find potentially hazardous asteroids, the NEO (Near-Earth Object) Surveyor, is set to launch no earlier than September 2027.

NASA was officially tasked with finding 90% of potentially hazardous asteroids larger than 140 m in diameter in 2005 by the end of 2020. Scientists have made progress but are not quite there yet.

An asteroid large enough to wipe out a city hits about once every 100-1000 years on average, but they usually hit sparsely inhabited parts of the planet or the ocean. Asteroids that are large enough to cause a mass extinction or wipe out civilization (~10 km) hit Earth even more rarely, about every 100,000 years or more on average. The last one that hit killed off the non-Avian dinosaurs 66 million years ago. For all we know, we might be due for another. Don’t worry though, astronomers have not detected one of that scale likely to hit us soon, not yet anyways. Asteroids are not disasters to lose sleep over, but they are disasters that we should prepare for. Otherwise, if we discover a giant asteroid on a course to collide with Earth in the next six months, not even Bruce Willis will be able to save us.

After detection, the other part of planetary defense is deflection. Once you have identified the asteroid that is on a collision course with Earth, how do you prevent it? A popular depiction that appears in films like Armageddon is of course to destroy the asteroid with bombs or projectile weapons. The problem with this approach is that it will leave a debris field that might hit Earth anyways. The debris would also devastate multiple parts of the surface rather than being concentrated in one area, making it more dangerous than it otherwise would be.

The more feasible approach is to use a projectile weapon to redirect the asteroid. This was tested in 2022 by DART (Double Asteroid Redirect Test), the first asteroid re-direct mission dedicated specifically to planetary defense. The DART mission used a projectile to collide with asteroid Dimorphos, a 160 m (530-foot) “moonlet” of the larger asteroid Didymos (D = 780 m or 2560 ft.), on September 26, 2022, successfully altering Dimorphos’s orbit.

Alternatives to using projectile weapons is to use a gravity tractor. In this case you send a spacecraft to fly alongside the asteroid and the spacecraft’s gravity slightly tugs on the asteroid until its course is shifted. This takes longer but is less likely to cause debris that would hit Earth anyways. A related option is to use a spacecraft that attaches itself to the asteroid and pushes or pulls it using thrusters.

If humans can alter the course of asteroids, this does more than ensure that we can protect our home planet from asteroid strikes. It also means that we eventually could control and reach asteroids for other purposes, such as to mine resources or to create dwellings.

For example, some asteroids are rich in critical minerals containing metals important for electronics. A major problem with the transition to renewable energy, and the more recent growth in demand for data centers for AI use, is reliance on mining practices that are destructive to the environment and in some cases sourced from organizations with unethical labor practices depending on the country of origin.

While I am not suggesting that we strip mine every asteroid or that the green and AI transitions need asteroid mining to become sustainable, asteroid resources could become a long-term solution to the problem of electronics manufacturing relying on environmentally destructive and ethically questionable mining practices on Earth since most asteroids are unlikely to have indigenous life and the extraction methods would involve robots not human laborers (the plot of The Expanse notwithstanding).

Asteroids are also good candidates for natural space stations and future dwelling places for humanity and other Earth life. I am not saying we leave Earth, but since humans and other earthlings are vulnerable to extinction by a major impact event as long as we are restricted to one planet, settling other worlds would put our eggs into more than one basket.

Why not just settle Mars instead of tiny asteroids? I am not opposed to settling Mars, but there are drawbacks to living on a planet if we move off-Earth. For one thing, the larger gravity well would make it expensive to travel there and back. Settling an asteroid would mean that future settlers could travel more freely across the solar system with less fuel if their asteroid ran out of resources. Also, unlike the relatively gigantic Mars, future settlers could alter the asteroid’s orbit relatively easily or choose to leave the solar system altogether and become interstellar nomads. DART proved that we can alter the trajectory of small asteroids. It is not obvious that we will be able to alter the trajectory of a planet any time soon. That is probably a good thing for now. Furthermore, Mars in particular may have life, which in that case it could be argued that Mars belongs to the Martians.

In this way, planetary defense, like AI safety, for example, represents both a response to a threat and investment in an opportunity. If we can mitigate the threat of asteroids colliding with Earth and destroying civilization, we may also be able to utilize asteroid resources for the benefit of life on Earth and to move beyond Earth into the wider solar system and beyond.

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Mercury is like Earth’s Moon in many ways. It is comparable in size (radius = 2440 km or 1516 miles for Mercury vs. 1740 km or 1080 miles for the Moon), dominated by the same types of features and terrain (craters, lava plains, etc.), and it is also considered to be lifeless and likely geologically dead. Mercury long ago ceased to be hot enough to have molten rock to feed volcanic eruptions. Its surface has changed little in a billion years like the Moon.

Nonetheless, also like the Moon, Mercury has its surprises. Strangely, Mercury still has a global, albeit residual magnetic field, whereas a larger planet like Mars, does not. Also, Mercury, despite being the planet closest to the sun with temperatures as high as 430 °C (800 °F), may have water ice in permanently shadowed craters in its polar regions.

The planet Mercury has a long history dominated by volcanism, tectonics, and impact craters. As we move into the Anthropocene of the solar system, Mercury may also have significance as a representative of the non-living world. Despite being lifeless, Mercury serves as a record of the geologic history of the solar system and represents just how strange a planet can be despite initially looking fairly featureless. Mercury may also be come a test of the concept exogeoheritage, that non-living geologic systems can have intrinsic value like organisms and ecosystems. Our descendants may deconstruct Mercury to build a Dyson sphere, but should we do that? Is there intrinsic value in worlds even if they are not places where life could exist or where humans could settle? What we do with Mercury may determine how our species relates to the cosmos going forward.

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I was talking with a friend at the Lunar and Planetary Science Conference a few years back who was studying the planet Mercury and an attendee of the NASA Mercury Exploration Assessment Group (MExAG). He was talking about how challenging it was getting the public excited about the planet Mercury. According to my friend, the main idea they come up with was hosting a concert by a singer who had a crater on Mercury named in their honor.

As a science communicator, I see no problem bridging science and popular culture, but I don’t think we have to rely on popular singers to make Mercury interesting. We just need to tell Mercury’s story, which begins with the geologic timescale. This because to tell a story, you need to know the chapters.

Mercurian geologic timescale

On Earth, transitions in the history of life, specifically mass extinctions play an important role in defining geologic time periods. For example, the present eon in Earth’s history (the Cenozoic) begins with the extinction of the dinosaurs 65 Ma (million years ago). Since there is no life on Mercury, as far as we know, geologic time periods are defined by volcanic and and major impact events.

The major time periods of the Mercurian geologic timescale are the Pre-Tolstojan, Tolstojan, Calorian, Mansurian, and Kuiperian.

Pre-Tolstojan to Tolstojan (4.5-3.9 Ga)

The earliest period in the geologic history is the Pre-Tolstojan. The Pre-Tolstojan begins with the formation of Mercury about 4.6 Ga (billion years ago) and ends with the formation of the Tolstoj crater basin around ~4.0 Ga. During the Pre-Tolstojan and Tolstojan, the solar system was still filled with protoplanets and planetesimals colliding with each other and the forming planets, including Mercury. As a result, the oldest terrain on Mercury is heavily cratered terrain where the impact craters are separated by rugged, hilly intercrater plains. The intercrater plains likely include debris from these ancient impacts events. Also during this time, Mercury was still hot enough to have volcanic eruptions. Some of the oldest craters are filled with basalt from hardened lava that filled the primordial basins when fissures were opened by catastrophic collisions. Many of the major geologic features characteristic of though not necessarily unique to Mercury, including gain multi-ringed crater basins, were formed during this time.

Calorian (3.9-1.7 Ga)

By the end of the Tolstojan (~3.9 Ga), the rate of impact events on Mercury had slowed down but volcanic eruptions were still frequent. The Tolstojan is followed by the Calorian, which is named after Caloris basin, a giant polar basin on Mercury. The Calorian age begins with formation of Caloris basin. The early Calorian is defined by the formation of extensive smooth plains found both within craters and between craters. In contrast to the rugged intercrater plains, the smooth plains are believed to be from gigantic eruptions where the surface was flooded with lava. In addition to lava eruptions (also called effusive eruptions), Mercury also had explosive (gas-driven) eruptions where the Mercurian crust had pockets of volatiles, like liquid water. In most extreme cases, the escape of volatiles from the upper crust of Mercury led to the surface collapsing resulting in nobby, broken terrain called chaos terrain, analogous to badlands terrain on Earth.

Over the course of the Calorian, Mercury cooled, and as it cooled it shrank. The shrinking of Mercury did two things. It resulted in the formation of lobate scarps, essentially wrinkles in the crust of Mercury, akin to the wrinkles in a raisin from the shrinking of the raisin as it dehydrates. The shrinking of Mercury also created internal pressure that made it harder for volcanic eruptions to occur. This leading to a dropping off of volcanic eruptions in the late Calorian. Volcanic eruptions were much less frequent and mostly connected to impact craters where the impact event opened a fissure.

Mansurian (1.7 Ga-280 Ma)

The beginning of the Mansurian age is marked by the appearance of fresh-looking craters that lack the bright rays associated with youngest craters on the Moon, including Mansur Crater itself, which defines the base of the Mansurian age system. By the Mansurian, the giant lava eruptions that formed the smooth plains had long since ceased, except for occasional impact-related instances of volcanism. The dominant geological process on the surface of Mercury was the relentless battering of its surface by asteroids, comets, and other space rocks. Since Mercury is closer to the sun than Earth, objects collide with its surface with higher velocity and with greater frequency compared to farther out in the solar system. The population of space rocks at the orbit of Mercury is not higher necessarily, but the population is more dense since there is less volume within Mercury’s orbit compared to, say, Earth’s orbit. This also leads to to more frequent impacts. Other than impact events and possibly occasional eruptions of lava to flood new craters, not much happened during the Mansurian on Mercury.

Kuiperian (280 Ma-Present)

The Kuiperian age represents the present epoch of Mercury defined by the first appearance of rayed craters, including Kuiper Crater itself, craters that are both fresh looking and have the characteristic rays of the youngest lunar craters. Mercury had changed little in almost two billion years when something unusual happened. On March 29, 1974 a fragment of Earth flew past Mercury. This fragment of Earth, however, was able to transmit information back to Earth. This was the Mariner 10 spacecraft, the first successful flyby of the planet Mercury. The next major mission to explore Mercury, MESSENGER, arrived in 2011. MESSENGER also became part of Mercury when it crash-landed on Mercury’s surface in 2015 as its end of mission.

Mercury in the Anthropocene and beyond

The fragments of Messenger could be considered the first traces of human activity on Mercury, marking 2015 as the beginning of the Mercurian Anthropocene. The Anthropocene for the uninitiated is a proposed term for the period in Earth’s history where humans become a driving force in a planet’s geological processes.

Since Mercury is both unlikely to have life, though it can’t be ruled out completely, and more difficult to terraform than Mars, Mercury’s future in the Anthropocene as a planet looks grim. In Isaac Asimov’s anthology, I Robot, for example, it is described mainly as mining world. A recent idea is to deconstruct Mercury entirely and make it into a Dyson sphere, a hypothetical structure that an advanced stellar-scale civilization might build to capture the energy from a star by enclosing it entirely or almost entirely with a shell or swarm of artificial structures. Most proposals involve leaving an open sliver at the stellar or solar equator to provide light to any inhabited planets. This would in theory allow humanity to harness the full energy of the sun and use it for things like interstellar travel.

Dyson spheres would be relatively easy to detect because of the waste heat that would need to be radiate into heat, SETI researchers have made attempts to search for Dyson spheres areound nearby stars. So far none have been detected other than the initially tantalizing case of Tabby’s star. Should we build a Dyson sphere if it means deconstructing an entire planet like Mercury?

Recent thinking from the SETI community is that Dyson spheres may not be common since it implies a focus on unlimited expansion that is coming to be seen as unsustainable in the long-term. In short, civilizations that are able to persist over geologic timescales, and hence long enough to be detected, may reach an equilibrium point where they are able to exist within the constraints of their planetary system for an indefinite period time rather than maximize their energy consumption and output like our current civilization. This has been called the sustainability solution to the Fermi Paradox. In this scenario, the most advanced civilizations cease to be detectable since they just look like a planet with a biosphere. A civilization like this is unlikely to build a Dyson sphere, and the fact that Dyson spheres have not been detected around other stars is at least consistent with this conclusion. This leads to the provocative question. What would be the cultural adaptations required to form a mindset that promoted this sort of civilization?

This brings us to the planet Mercury and how it can help shape our perspective on space exploration. A recent concept in space exploration is exogeoheritage. Exogeoheritage is inspired by the terrestrial concept of geoheritage, which sees non-living geologic features as having the same intrinsic value as living ecosystems and and cultural artifacts.

Exogeoheritage implies that non-living and non-technological systems have intrinsic value and that we shouldn’t just see them as raw materials for turning the cosmos into a giant suburb. The planet Mercury may not have life or be ideal for human settlement, but it is a unique world with its own history, processes, and character. We may one day decide to make Mercury into a Dyson sphere (to be clear I am not anti-Dyson sphere per se) and maybe that will be the right choice, but first let us make sure to appreciate Mercury and the other planets for their intrinsic value as alien worlds. After all, as the sustainability solution to the Fermi Paradox implies, our long-term future might not look like living in a Dyson sphere. In might just look like living in a healthy relationship with our home planets.

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Advances in environmental economics and the environmental humanities suggest a solution rooted in the long-term sustainability of continuous growth. In this case, advanced extraterrestrial intelligences (ETIs) have not been detected because current searches are for signs of civilizations focused on rapid economic growth from industrialism and colonialism, which may not be sustainable over timescales that allow for a civilization to likely be detected (>10,000 years).

This poses a problem for the search for ETI since a civilization that does not disrupt nature would be much harder to detect If a planet with a technologically advanced civilization starts to just look like a planet with a biosphere after a short window of time. This would significantly reduce the time during which a civilization is detectable over interstellar distances.

On the other hand, what looks like pollution from our vantage point may actually be a civilization intentionally disrupting planetary processes in a way that maintains long-term planetary habitability and the long-term survival of a civilization. In this way, long-lived civilizations that have learned to have a healthy relationship with their planet may still be detectable based on the same technosignatures used to detect civilizations still learning how to live sustainably on their home planet. This also provides concrete ideas of what a long-lived technologically advanced civilization may look like on Earth.

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Calculations have been done which suggest that a technologically advanced civilization simply going from star to star, at speeds significantly less than the speed of light, could colonize the entire galaxy in just a few million years. While this is a long time from a human history perspective, it is the blink of an eye cosmologically and geologically. This leads to the Fermi paradox. If colonizing the galaxy is this easy (relatively), why haven’t we detected more, or any, ETI civilizations? More provocatively, why isn’t our planet in one of these civilization by now?

Classic Fermi paradox solutions include the alien zoo hypothesis, or the prime directive hypothesis, that the aliens are out there but hiding themselves purposefully from us because we are not ready. Another explanation is the dark forest hypothesis, that there is a hostile alien presence that intentionally destroys any civilization that becomes advanced enough to be detectable over interstellar distances, presumeably to prevent competitors on the cosmic scene. Another explanation is simply that most technologically advanced civilizations destroy themselves with nuclear war or environmental destruction before they can last long enough to be detect with current technology.

The galactic zoo hypothesis and the dark forest hypothesis are popular science fiction but almost impossible to disprove. Any challenges to the hypothesess can always be blamed on powerful aliens hiding things from us (aliens of the gaps?). The latter hypothesis, that most civilizations don’t last long enough to be detected, is more likely in my opinion.

On the other hand, we only have a sample of n =1 technologically advanced planetary civilizations. As a result, we really can’t be certain of how long the average technological advanced civilization lasts or whether the average lifespan of a civilization is long enough to make detection likely.

An explanation gaining popularity is that truly long-lived civilizations learn to use technology in such a way that it doesn’t disrupt the biosphere in the ways that are detectable over interstellar distances. As a civilization get more advanced, its technological processes begin to look more like natural processes until they merge with the biosphere from the perspective of an interstellar observer.

This solution comes from ecological economics and focuses on the proposed unsustainability of a focus on rapid and infinite economic growth and technological development, which depletes planetary resources and threatens planetary habitability. A civilization that seeks to last over geologic timescales, it is argued, will need to abandon this approach in favor of long-term sustainability. In this way, civilizations that last beyond a certain bottleneck of rapid technological advancement and economic growth may be very hard to distinguish from a biosphere lacking an advanced technological civilization, especially from interstellar distances.

This makes the concept of “technosignature” complicated. By analogy with “biosignatures,” technosignatures are supposed to be indications of technology on a planet. This could range from a crashed alien spacecraft on the Moon to industrial pollutants, like CFCs, in the atmosphere of an exoplanet.

The problem with a lot of current technosigantures is that they assume a civilization that looks like ours, one that pollutes its atmosphere, gives off high intensity electromagnetic signals, and is constantly disrupting its planetary environment through ever-growing production and consumption needs. We don’t necessarily know what a technosignature from a technologically advanced but non-colonizing, non-expansionist or non-industrial civilization in homeostasis with its planetary environment would look like.

While this is encouraging from the perspective of possible futures of civilization, from a research perspective it is troubling. It could mean that the only civilizations we can detect are immature civilizations that will either quickly evolve into non-detectable civilizations, indistinguishable from the biosphere, or simply wipe themselves out in a geologically short time period. The most easy to detect civilizations may also be the most short-lived.

Since the most common technosignatures are from disruptions of planetary processes caused by large scale economic or technological projects, it could be argued that most technosignatures searches would not helpful in detecting civilizations that have taken a more sustainable route where they exist in metabolic equilibrium with their planet. On the other hand, these civilizations may do things that look like pollution from our vantage point but are actually the biproduct of planetary stewardship.

Phenomena which we associate with pollution could also be a biproduct of a civilization effectively managing its planetary environment. For example, industrial greenhouse gases in the atmosphere of an exoplanet would also occur if a civilization was acting to stave off a coming ice age to maintain planetary habitability. A civilization may construct a Dyson sphere but fill it with habitats that support vegetation enabling artificially contained ecologies that have the potential to last much longer than those that exist on planetary surfaces in less controlled environments.

Furthermore a crashed alien probe may not be evidence of an advanced civilization that is looking for new economic resources to exploit, but one that is curious about the universe and sending robotic probes to explore, an idea explored in depth in science fiction.

If these hypothetical long-lived planetary civilizations also give off signals that appear to be distruptions to planetary processes, it means that there may be a larger time window of detection than otherwise assumed. This also has implications for the Fermi paradox because the absence of such technosignatures many not mean that civilizations are becoming non-detectable as they get more advanced.

This still does not mean that these civilizations do or don’t exist, but it does mean that it is still worth searching for technosignatures. Furthermore it gives our own civilization some concrete ideas of what a more sustainable future for a technologically advanced planetary or multi-planetary civilization might look like. This is important since ultimately we would want the future for our own civilization.

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Over the past 4.5 Billion years since its formation, Mars has been scarred by craters, covered in lava from giant volcanic eruptions, covered in water by floods and possible transient oceans, and rivers, and covered in dust by eons of being a windswept desert. Recently, Mars has also entered the Anthropocene with arrival of human-built rovers, landers and orbiting spacecraft. Since Mars is the only planet other than Earth to have its own satellite array, you could say it is one of the most technologically advanced worlds in the solar system, second only to Earth, or the most advanced if you consider that it is entirely populated by alien robots, aliens from Earth that is.

Also, like Earth, Mars is experiencing an ecological transformation as it is likely that humans have contaminated Mars with microbial Earth life or will soon despite our best efforts to avoid it. Instead of Martians invading Earth, it is a case of Earthlings invading Mars.

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The Martian geologic timescale is divided into four epochs: the Pre-Noachian, the Noachian, the Hesperian, and the Amazonian. On Earth, the boundaries between geologic time periods are determined by mass extinctions. On Mars and the other planets of the solar system, geologic time period boundaries are determined by volcanic eruptions and major impact events.

The Pre-Noachian begins with the formation of the planet Mars ~4.6 billion years ago (Ga) to ~4.1 billon Ga During the Pre-Noachian, Mars was likely still cooling. vey early Mars may have had a global magma ocean which cooled to form the Martian crust. The Pre-Noachian also was likely a time of frequent impact events from collisions between early Mars and protoplanets, the building blocks of the inner planets. By the end of the Pre-Noachian the surface of Mars had cooled enough that liquid water could exist at its surface, part of the transition to the Noachian Epoch.

Figure 1. Mars during the Noachian? Image credit: NASA/GSFC

The Noachian (~4.1-3.7 Ga) is not far removed from the Pre-Noachian. Named for the Noachis Terra region on Mars, the Noachian epoch was dominated frequent impact events fom colliding asteroids or protoplanets. The major Martian impact basins, like Argyre Basin and Hellas Basin, likely formed around this time. It is even possible that the northern lowlands (Vastitas Borealis) in the Martian northern hemisphere are the result of giant impact by an asteroid ~500 km or ~300 miles across. The two moons of Mars, Phobos and Deimos, may be fragments from this collision. A sample return mission could help confirm whether the Martian moons are fragments of Mars or captured asteroids. The Russian space agency, Roscomos, attempted a sample return mission (Fobos-Grunt) in 2011. It unfortunately failed to leave Earth’s orbit.

Figure 2. A helpful global elevation map of Mars for context. Image credit: Emily Lakdawalla at the Planetary Society originally adapted from a NASA map.

The Noachian is also a time when Mars likely had a thicker atmosphere. There is geochemical evidence from the Mars Curiosity and Perseverance rover missions that lakes of liquid water once existed on the surface of Mas and orbiter image data reveal evidence of possible paleo-shorelines of Martian oceans and valley networks, which may have been rivers. If there ever was a time when Mars could have hosted life, it would have been around this time. This all changed when Mars lost its thicker atmosphere. This was likely due to solar wind stripping the atmosphere away due to a weak or absent magnetic field. This transformed a relatively clement ancient Mars to the barren, desiccated wasteland it is today.

The Hesperian epoch (3.7-3.0 Ga) is named for Hesperia Planum, an ancient lava plain on Mars. Hesperia Planum form during the Hesperian epoch, but the Hesperian is no longer tied to the volcanic plain. The Hesperian was a time of climate shifts. The valley networks disappeared and ice sheets covered Mars at time. These ice sheets occasionally melted causing great floods that created transient lakes. The Hesperian is also when the giant Arizona-sized volcano, Olympus Mons, in the Tharsis region of Mars began to erupt, accumulating so much lava over millions of years.

The next and final epoch in Martian geologic history is the Amazonian epoch (3.0 Ga-Present). It is also longer than the three previous epochs, combined, ~3 billion years. The Amazonian is marked by a gradual reduction in volcanic activity. Mars also experienced much fewer impacts than in previous epochs. By the Amazonian, the atmosphere was worn thin by solar wind and eventually liquid water could no longer be sustained on Mars except for brief periods at the equator or in deep basins like Hellas basin, where the atmospheric pressure is slightly higher. It is during the Amazonian that Mars became the planet it is today, dry, barren, windswept, and almost no atmosphere.

Figure 3. Olympus Mons, the largest volcano in the solar system. Image credit: NASA/JPL-Caltech.

Nonetheless, even Amazonian Mars has its surprises. Volcanic activity, although less common in the Amazonian, may have persisted until 180-200 million years ago, the recent past in geologic terms. Mars was long thought to be geologically dead, but it may just be dormant. It is also possible that transient puddles of liquid water can be sustained for a few hours on the floor of Hellas basin during the warmest day of the Martian year. This does not mean life could exist at the surface, but it does make the case for deep subsurface layers of brine where life could still linger on Mars more promising.

A new era history of Mars began when on December 2, 1971, the Soviet Mars 3 lander touched down on red planet. Communication with the probe abruptly ended seconds later, but it was beginning of series of robotic visitors to the red planet. The number of robots on Mars continues to grow as the United States, ESA, China, and India have all sent orbiters, and landers and rovers in the case of China and the United States. These robotic explorers are expanding our knowledge of Mars and may be paving the way for humans to settle Mars.

Until the 20^th century Mars had an atmosphere, albeit not much of one, and a geosphere. It did not have a biosphere let alone a technosphere. Mars, like Earth and the Moon, now has a technosphere because of the many active orbiters and rovers. Early in solar system history, Earth and Mars both experienced catastrophes, meaning they both experienced dramatic, functionally irreversible changes to their planetary environments. For Mars, it was the loss of its atmosphere. For Earth, it was the emergence of life. In the next century, Mars may experience a similar catastrophe.

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This past week, I had the privilege of attending the IAUS 404 symposium hosted by the Blue Marble Space Institute of Science (March 2-6 2026) on SETI and technosignatures. As a planetary scientist, the talks which stood out most to me were talks related to solar system science. Several talks covered using ML models to search for anomalies on planetary surfaces which could be potential technosignatures. There was also discussion of distinguishing a biosignature from a technosignature on a planetary surface. This was particularly interesting since it reveals how the difference between biology and technology is more like a spectrum than a clear categorical distinction.

When thinking about how to detect extraterrestrial intelligence, we typically think of advanced technology that only humans build, like interplanetary spacecraft or radio telescopes, but other organisms also construct artificial structures. Beavers build dams, termites build mounds, etc. If technology is defined mainly as an organism extending their limbs by augmenting elements of the natural world to accomplish a task (when you use a hammer you are essentially “augmenting” another limb), beaver dams or termite mounds could arguably be technosignatures, albeit not the technosignatures we might have in mind.

While attending the conference, I was struck by two parallels between planetary science and the broader field of SETI. One parallel is the interdisciplinary nature. The other parallel is the need to think beyond parochial, Earth-centric categories.

Planetary science draws upon the fields of astronomy, geology, chemistry, meteorology, and even biology to understand planetary processes. This is because planets are complex systems.with their own geochemical, atmospheric, and geological cycles. We also need to understand planetary orbits and the orbits of the moons around their parent planets since they also affect planetary processes.

The climates of Earth and Mars are impacted by Milankovitch cycles, because of gradual changing in the shape of their orbits and their axial tilt, leading to changes in climate. The moons of the giant planets are affected by gravitational influences between the other moons and the parent planet, or tides, leading to tidal heating and possible subsurface oceans. Understand the influence of tidal forces on the icy moons was a major part of my research as an intern at JPL and my doctoral work at the University of North Dakota.

In a similar way, SETI is also interdisciplinary since it draws from all the field of study needed to search for and understand extraterrestrial civilizations. We must understand astronomy and planetary science so that we know where to look. We must understand biology and ecology so that we know how extraterrestrials would function and evolve. We must also understand sociology and engineering to understand what they would build and what choices their societies might make. Since many technosignatures, like Dyson spheres and space garbage, are archaeological in nature, we also need to think about archaeology and how things are preserved.

The other parallel is more philosophical in nature and it has to do with the need to move beyond our planetary context. When I participated in a planetary geologic mapping workshop in Flagstaff, AZ a few years ago, I learned that in planetary mapping descriptions of geological featues must be carefully distinguished fom interpretation.

This is because we cannot actually land on the surface and walk up to a geologic feature and confirm what it is and how it formed. A feature that looks like a volcano or a river channel on one planet may have been formed by a completely different process. For example, channels on Mars that look like erosion channels formed by running water were actually formed by the sublimation of carbon dioxide ice. There are also features on other planetary bodies that don’t have a clear parallel on Earth, like double ridges on icy moons, the coronae on Miranda and Venus, or the spider-like araneiform features on Mars.

For this reason, when exploring planetary surfaces we need to avoid premature interpretations based on descriptions. Something might look like a river channel on Mars or Titan, but it might have been formed by a completely different process. This means that each planet is unique and has its own geological features and processes. We cannot assume each planet is the same.

This same principle is also true of extraterrestrial civilizations. One example is the assumption that evidence of technosignatures will come from the disruption of nature. Most technosignatures tend to either be the result of pollution, like CFCs in an exoplanet atmosphere, or radical alterations of nature. Building a Dyson sphere, for example, would likely require the deconstruction of half a planet the size of Mercury to get the requisite materials. A topic that came up during the symposium was the possibility that a civilization might develop its technology in a way that enhances nature rather than disrupting it. Civilizations that build Dyson spheres may exist but be relatively rare compared to civilizations that advance though pathways that are less obvious at interstellar distances.

This bias towards technosignatures that our civilization would recognize as obvious is also true for planetary technosignatures. It is easy to assume that structures built by a non-terrestrial civilization will resemble human-made structures, but the way humans build structures may also be a consequence of the human body plan. Aliens shaped more like termites, for example, might build something that looks more like a giant termite mound.

In astrobiology there is an emerging concept called an agnostic biosignature. It is a biosignature that can be detected which is not necessarily organic or carbon-based. Agnostic biosignatures attempt to identify life as we don’t know it, that is, independent of their specific biochemical pathway. An popular example of life as we don’t know it is silicon-based life, a hypothetic form of life where silicon replaces carbon in its biochemistry.

In the same way, could a methodology for detecting an agnostic technosignature be developed? Common technsignatures are those we would expect from industrial civilizations like ourselves that pollute the environment and radically alter nature. Could there be a way to identify technosignatures that don’t assume this or any particular technological pathway? That will be the topic for a future ML project.

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I applied the Xenarch model to the Apollo 11 landing site based on Lunar Reconnaissance Orbiter Camera (LROC) images. Using the LROC image data, the earliest versions of the model (collectively Xenarch Version 0) were able to identify the Apollo 11 lander as one of the 10 top anomalies but not as the number one anomaly. Instead, the earliest versions of the model identified a field of boulders in a nearby crater as the number one anomaly.

Xenarch Version 1, which reduced the weight of the edge regularity metric and made it more balanced with the other metrics, was more accurate. Version 1 identified the Apollo 11 lander as one of the top 3 anomalies, but still identified a boulder field as the top anomaly. Xenarch Version 2, using higher resolution imagery from the Chandrayaan 2 Orbital High-Resolution Camera (OHRC), was able to identify the lunar lander as the number 1 anomaly with a 99.58% confidence rate.

The model is still a work progress, but the identification of a known artificial structure as the number one anomaly in the test dataset is a big step for this model. Once fully developed, Xenarch could also be applied to search for other types of technosignatures, including atmospheric technosignatures on exoplanets or objects passing through the solar system as interstellar interlopers.

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When I first decided I wanted to be an astronaut at the age of twelve, I knew that I needed to major in a STEM field in college but couldn’t decide. My other major interests at the time were history and archaeology. Although I wanted to be an archaeologist on Mars, I ended up settling for the closest thing, a geology. This is because geology is history. As a geologist you study the history of Earth through rocks that record the evolution of life and the environment. If you know how to read the rocks, they reveal a history of ancient ecosystems, rivers, oceans, volcanoes pole shifts, and deserts. These aren’t just fun but otherwise irrelevant facts either. For example, finding fossil fuel deposits requires an understanding of the environments that form coal and oil deposits to identify the correct rock types and geologic settings.

This same fact applies to the geology of other planets. The surfaces of the Moon, Mars, and other planetary bodies record the history of the solar system, a record of catastrophic impacts, volcanic eruptions, the formation and drying out of oceans and rivers, and, in one case at least, the formation of life.

The Moon for example, is divided into four periods. These are the Pre-Nectarian, the Nectarian (geologists are ever-imaginative with naming time periods), the Eratosthenian, and the Copernican.

The Pre-Nectarian period dates from the Moon’s formation about 4.5 billion years ago to the formation of the Mare Nectaris basin, about 3.9 billion years ago. Understandably not much is known of this very early period in the Moon’s history. The Moon had only recently formed and was probably still hot enough to have volcanic eruptions, which may have led to the outgassing of water vapor that could have contributed to some of the Moon’s modern polar ice deposits and ancient transient lunar atmosphere. Of course, comet strikes and impacts by water-rich asteroids likely still contributed to the lunar water inventory.

The origin of lunar water shows how, like with fossil fuels on Earth, a vital resource for human civilization to be sustained on the Moon may have ancient geologic origins that also reveal significant details about the Moon’s evolution and geologic history. The Pre-Nectarian is also probably when the lunar highlands, the lighter colored and rougher terrain visible on the Moon’s surface, formed. The current idea is that the lunar highlands formed from a “magma ocean” where lighter minerals, like anorthite, accumulated at the surface while denser minerals, like olivine and pyroxene, sank into the core and mantle.

The Pre-Nectarian is believed to be dominated by frequent impacts events from the higher number of space rocks flying around the primordial solar system, compared to today. Giant crater basins older than the ones prominent on the Moon’s surface today probably formed as result of giant impact events common in the pimordial solar system, but they were degraded over time by later impact events. The heavily catered lunar highlands likely hide the eroded ghosts of ancient crater basins from collisions which may have almost destroyed the early Moon.

The Nectarian period starts around 3.9 billion years ago and is marked by formation of Mare Nectaris and other large basins that formed at the time. The surface of the Moon during the Nectarian was likely dominated by this impact crater basin and its extensive debris deposits associated with Crater Janssen and the valley Vallis Rheita as well as othe large basins. The Nectarian is more or less a continuation of barrage of impacts that defined Pre-Imbrian periods of the Moon’s history. It also a continuation of the Pe-Nectarian in tems of geologic activty since there is geologic evidence that the Moon may have had a weak magnetic field at this time.

The Imbrian period begins around 3.8 billion yeas ago with the formation of the Mare Imbrium basin. The Imbrian period is also significant in marking a drop off in the rate of impact events compared to Pre-Imbrian times. This could be related to the end of the late heavy bombardment. The late heavy bombardment is a solar system-wide event or period during which the frequency of impact events from large >1-10 km was much higher than it is today. The Imbrian period is also probably when most of the lunar maria form. The lunar maria are the darker regions visible on the Moon. They are vast plains of basaltic rock which were once magma seas from molten rock filling recently carved impact basins.

The Eratosthenian lasted from about 3.8 billion years ago to about 1 billion years ago. It is name for Eratosthenes crater and represents the transition from the geologically active Moon of Pre-Imbrian and Imbrian times, with a continuous rain of large impactors (the rain continues today but >1 km sized objects are far less frequent), magma seas, sporadic volcanic eruptions, transient atmospheres, and primordial magnetic fields, to the Moon of geologically dead Moon of today. If Pre-Imbrian times represented a geological golden age for the Moon. The Eratosthenian marks the silver age, when there is still a sign of ancient glory but also decline. The Eratosthenian contains the last evidence of volcanic activity on the Moon. Also, most post-maria craters that lack crater rays are considered Eratosthenian. The Eratosthenian period could be seen as the the period over which the Moon slowly dies geologically as it runs out of heat.

The current geological epoch of the Moon’s history is the Copernican epoch named after Copernicus crater, one of the rayed craters. Rayed craters have bright streaks or “rays“ that are eroded in geologically brief periods of time by subsequent impacts. Since the dawn of the Copernican, the Moon has changed little.

The geology of the Moon during the Copernican period is dominated by impact processes. Large impact events are much rarer though and the most important impact process governing the moon today are micrometeorite impacts. The tiny meteorites have rained down on the lunar surface for billions of years, eroding its mountains and crater rims as efficiently as wind and rain erode geologic features on planetary bodies with atmospheres.

Since the earliest organisms with eyes probably only evolved in the last 600 million years or so, it could be said that Moon has looked the way it does since before there were eyes (on Earth anyways) to see it.

The Moon’s surface remained relatively unchanged for a billion, until September 13, 1959. This is the that the Soviet Luna 2 spacecraft crash-landed into the ancient plains of Mare Imbrium. Since then, human activity has been altering the lunar surface in unique and rapid ways. In the future, this may involve the mysterious self-organizing matter that we call life and civilization.

As humans set out into space, possibly to establish settlements and prospect resources, life may begin to play a major role in the geologic history of the Moon, as it has on Earth for 4 billion years. On Earth, geologists talk about the Anthropocene, a proposed name for a new epoch in Earth’s history where humans are a significant driving force in Earth’s geology. The Anthropocene may very well be spreading across the solar system through our robotic probes and eventually human missions. This is likely to be especially true for the Moon in the near-term. The Anthropocene may not last for long, however. The Anthropocene may only be a transitional phase in the history of the solar system before the solar system becomes colonized by post-biological intelligence. Perhaps the solar system is in the Anthropocene but about to enter the “Clawd-ocene.”

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In the book Pale Blue Dot, The astronomer Carl Sagan once described the Moon as “boring” in contrast to the more complex and potentially habitable surface of Mars. I admire Carl Sagan and agree with him on many issues, but this is one area where I think he was mistaken. The Moon does not seem like much at first, but more recent studies show that the Moon is indeed an interesting world with many mysteries even if humans never again set foot on its dusty plains. It may be geologically dead, but the Moon has its mysteries.

For example, recent studies suggest that at least some of the lunar water abundant at the lunar south pole might have come from ancient lunar volcanoes rather than comet or asteroid impacts. During these eruptions, the Moon might have had a tansient atmosphere of water vapor that lasted for at least a few thousand years. This brief atmosphere might have been thicker than that of Mars at times. Albeit considering the Martian atmosphere is ~0.006 bars, or a thousandth of Earth’s atmospheric pressure at sea level, that might not be saying much. Still the Moon, had an atmosphere…

Furthermore, the Moon also has evidence of exotic terrain such as the irregular mare patches and lunar swirls. Also, although life on the Moon is unlikely, it cannot be completely ruled out.

As humans return to the Moon, there are plans to prospect water-ice for water and breathable air and mineral ores for building materials. GRU Space for example, even has plans to build a hotel, moonbase, and surface infrastructure including roads. Although not as ambitious, the company Interlune is also developing technology to deal with regolith contamination for lunar bases.

This has brought up questions about how this will affect the Lunar environment. True, the Moon doesn’t have native wildlife or native indigenous aliens for humans to drive into extinction or subjugate, as far as we know, but mining and other human activity will affect the landscapes of the Moon, including key geological features.

The Moon has some of the oldest surface geology in the solar system (~4.5 Ga), which could reveal key evidence regarding the early history of the solar system. These ancient terrains could be destroyed to make way for space hotels or mining operations. Historical lunar landing sites, such as from the U.S. Apollo missions and the Soviet Luna missions could also be under threat. Also, as unlikely as it is that there is indigenous life on the Moon, it cannot be completely ruled and something as unique as non-terrestrial life could be at risk from the introduction of Earth microbes, which we know can survive for years on the Lunar surface.

These potential threats have lead to discussion of mitigation strategies to protect historical heritage, like the Apollo landing sites, and geoheritage sites. Geoheritage is a concept that originated in the mid-20^th century. Geoheritage is an attempt to identify unique non-living aspects of the a planetary surface, such as mountains, cliffs, craters, or sequences of geologic layers, as being intrinsically valuable to a location and worthy of conservation for future generations to enjoy. There is even an accompanying term, geodiversity, which refers to the number of distinct geologic formations in a given area, akin to biodiversity, the number of different biological species in a given ecosystem. The work of preserving geoheritage is referred to as geoconservation.

The discovery of indigenous Moon life aside, the main natural conservation efforts on the Moon, as well as other bodies such as Mars and asteroids, will involve geoconservation. There have already been several papers on exogeoconservation, which refers to geoconservation on other planetary surfaces than Earth. Proponents of exogeoconservation, suggest international agreements be made that would protect future exogeoheritage sites. On the Moon, this might include the Chang’e 6 landing site, from which some of the youngest dated lunar rock samples have been returned (about 2.8 billion years old). On Mars, obvious candidates for future exogeoheritage sites would include Jezero Crater because of its importance for astrobiological research.

At first, building lunar hotels might seem at odds with the goals of exogeoconservation or space heritage protection, but this does not need to be the case. It could be argued that the builders of both moon bases for scientific research and lunar hotels would have a vested interest in preserving historically or geologically significant sites. After all, where are the tourists going to go? There could even be a partnership between space hotels and international organizations tasked with space heritage conservation to coordinate sites that would be interesting both to scientists or historians and to tourists.

Also, if humans do end up living on the Moon long-term and build a lunar civilization, preservation of cultural and scientific heritage on the Moon will be even more important to would-be lunar settlers. At that point, Lunar cultural and geoheritage will represent the unique history of Moon-dwelling humans and their home environment. In this way, settlement of the Moon and conservation of what makes the Moon unique do not need to be at odds with each other.

This of course makes conversations about space heitage even more impotant. If our descendants on the Moon are going to have scientific and cultural heitage to remind them of their identity as “Lunarians“, it is our responsibility to ensure that there is heritage left for them to teasure. In the meantime, space tourism could help ensure that by providing an economic incentive.

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For this project, which I have called the Xeno-Archaeology or “Xenarch” Project, I have developed a demo ML model for detecting anomalous features on planetary surfaces that the model cannot reconstruct as natural geologic features. The goal is to create a model that can be generalized to other planetary bodies. The model is not complete, but I have created a demo which I applied to the Apollo 11 landing site.

The demo uses variational autoencoder (VAE) model trained only on natural geology. The training dataset includes images of the Moon (LROC), Mars (HiRISE) and desert Earth desert imagery (Google Earth Pro) that has been vetted to avoid technological or biological structures to avoid unintentionally training the model on features that it is supposed to flag as anomalies.

Once the model was trained, I applied the model to test images of the Apollo 11 landing site. The model successfully identified parts of the Apollo 11 site as anomalies but not top anomalies, indicating more training is needed to refine the model. Nonetheless, this demo model has been able to identify artificial structures on the moon as anomalies that cannot be reconstructed as natural geology and represents the beginnings of a potential model that could be used for planetary SETI as well as for general planetary exploration in identification of unusual planetary phenomena of importance to planetary science researchers and future space resource companies.

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Planets, like people, are individuals. Each planet is unique, a self-contained system which is shaped by its distinctive mass, atmosphere, composition, and orbital position around its star. For example, on Mars there are gullies that were likely formed by the sliding blocks of subsurface carbon dioxide ice as the ice began to sublimate. These gullies look very similar to channels created by rain water on Earth. This demonstrates how very similar features on two planetary surfaces can be formed by very different underlying processes.

For this reason, we cannot assume that a planetary feature, such as a narrow groove that looks like a river, was formed by the same process across planetary bodies. This is the reason why planetary mapping is primarily descriptive rather than diagnostic. In planetary geologic mapping, we talk about “tholi,” “chaos terrain” and “lineae.” instead of just calling them “mountains,” “badlands,” “channels“ since such names are descriptive and imply an underlying process.

Badlands, for example are formed by wind and water erosion, but it is possible that that chaos terrain observed on Mars or Europa was actually formed by a completely different process. This is definitely the case for Europa which lacks an atmosphere to support running liquid water or wind at the surface. For this reason, most planetary geologists withhold diagnostic descriptions until we can get a rover, lander, or even human boots on the ground to confirm what a feature actually is based on close up examination, rather than simply based on orbital imagery data, the most common source of data we have on interpreting geologic features on planetary surfaces.

This is also relevant to the identification of possible artificial structures. Just as we don’t necessarily know the underlying formation mechanism of a feature on a planetary surface without closer examination, we also can’t say for certain what an artificial structure is used for and may not even be able to immediately recognize it as artificial. Just like human cultures do not all build the same structures, a non-terrestrial intelligence may build very different structures from those that we would expect from humans. Consider, for example, beehives and termite mounds, neither of which bear strong resemblance to human-made structures.

If we can’t trust our intuition about what is artificial and what is not when it comes to non-terrestrial artificial structures, how can we detect them? This is where fractals may be useful. Fractals and fractal geometry are the result of the tendency of certain processes to create structures that are scale invariant and self-similar. This means that they look the same regardless of scale so that each component of the structure resembles a small scale image of the whole. Natural coastlines are a common example of this phenomenon as pointed out in 1967 paper by the mathematician Benoit Mandelbrot, How Long is the Coast of Britain? Fractal patterns have already been suggested as a way to investigate planetary processes, since landscapes will vary in how fractal they are based on the process that formed them, for example, glacial erosion versus a tectonic structure created by fault activity.

This principle has actually been proposed as a way to detect artificial versus natural structures for national security reasons since human-made structures tend to be Euclidean, rather than fractal. This means they have a definite shape of lines and polygons that is not scale invariant. Suppose you have a town next to a coastline. If you zoom out from a 1 km scale to a 100 km scale, the general pattern of the coastline will not have changed but the town will appear much smaller with fewer visible details or have disappeared entirely. The pattern of a building or city will not necessarily re-appear on a larger scale. This approach has also been explored in archaeology as a way to infer patterns of human settlement. We know nothing about the architectural and spatial design preferences of non-terrestrial intelligences. Nonetheless, it is possible structures created using technology may all have a fractal signature that can be detected by machine learning even if such a signature is not visibly obvious to a human observer.

This is reflected in the fact that certain architectural forms were independently developed in different cultures across human history. Egyptians and Mayans both independently developed pyramids as a principle part of their architecture. There appears to be something about pyramids that just makes them intuitive for building, possibly because a pyramid is the most mechanically stable form you can make if you want to create something large and you do not have advanced materials that would make it easy to construct, say, a skyscraper. Certain structures built by civilizations may have similar characteristics which can be detected even if it is not a characteristic as obvious as a stone pyramid.

Investigating fractality is a way to investigate what processes shaped planetary surfaces. Fractality could be used to identify whether a landscape is likely to have been formed by known processes, such as glacial erosion or faulting, or anomalous processes. An anomalous process could be a previously unknown natural process, as in the case of Martian “spider” features, or it could be a cognitive process, that is, evidence of technology. The way fractals are already being used in both planetary science and anthropological research makes it a promising route for improving our ability to detect anomalous surface features and understand planetary surface processes.

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Conducting such a search leads to a significant issue, however. That issue is how do we know what a planetary technosignature looks like? One way around this issue is to use an unsupervised machine learning algorithm (such as an autoencoder) to reconstruct natural geology on planetary surfaces and flag what it can’t reconstruct as an anomaly for further analysis. Models could be developed for the unique geology of the Moon, Mars, and icy moons to detect potential non-terrestrial artifacts, but also evidence of weird undiscovered planetary phenomena that advances planetary exploration and resources useful to future astronauts and space settlers.

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Over 400 years ago, Johannes Kepler is reported to have thought that the circular craters on the moon were fortifications because he was unfamiliar with the process of impact cratering. This shows the propensity for humans to mistake orderly natural features for artificial structures.

On the other hand, it is also possible for us to misidentify artificial structures as natural features because we assume that everyone builds the same way that we do. This is part of the reason that the Nazca lines went undetected by European explorers…until they were viewed from the air. From the surface and on a small scale, the Nazca lines might look like natural trackways in the desert, but the appropriate scale reveals their artificiality.

Because of the assumptions involved, it is simpler to instead to consider what alien artificial structures do not look like. One way to do this is to train an unsupervised machine learning model (such as an autoencoder) on natural features that occur on planetary surfaces (craters, scarps, dunes, volcanic domes, etc.) so that it will recognize when something is not natural and flag it as an anomaly.

Supervised and unsupervised machine learning approaches have been proposed for the Moon for a variety of investigations related to planetary science and space resources, not just technosignatures. The main difference between supervised and unsupervised machine learning is that supervised machine learning algorithms are trained to identify specific features and also identify false positives of that feature. A supervised ML approach to planetary technosignatures might be to train an algorithm to distinguish between artificial and natural features based on a given definition. For example, features that circular with bright rims (craters) might be defined as natural features, whereas linear features high brightness might be defined as potential artificial structures. In other words, a supervised approach results in an “duck/not-duck” app for detecting aliens. While not necessarily the wrong approach, it is limited by assumptions about the nature and appearance of artificial structures which may not hold true for a non-terrestrial civilization.

An unsupervised learning approach to ML model building would allow for the model to focus on identifying natural geology until it can identify something that does not fit with what we know of natural geologic features. Once identified, the feature can be flagged and further analyzed to determine if it is likely to be of technological origin rather than just assuming it is based on pre-determined definitions of what is artificial in the search algorithm.

Although a variety of machine learning algorithms have been applied to the Moon, the approach is yet to be widely adopted by the planetary science and technosignatures communities. Furthermore, current proposals specifically for technosignature detection mostly focus on the Moon without extending to other bodies.

There is good reason for this since to do otherwise would add complexity to the project. If you are trying to see if an approach works, it is good to have a well-behaved control. The Moon is also a common choice because 1) its surface is very old and relatively unaltered, meaning a non-terrestrial artifact could remain on the surface for millions of years, increasing the probability of detection, and 2) the Moon’s proximity to Earth could make it a promising location from which to observe life on Earth, increasing the likelihood that a spacefaring civilization would take an interest in the Moon. Nonetheless, there are bodies beyond the Moon which could also have technosignatures, including Mars and possibly icy outer solar system moons.

As a planetary geologist with experience in quantitative modeling and geospatial data analysis, I am well positioned to develop an ML model (possibly an autoencoder) leveraging what we know of the geology of planetary surfaces to enable accurate anomaly detection that could aid technosignature searches. Such a model also has applications in broader planetary science research and resource detection.

I would start with training and developing an ML model for lunar geology. Once a model has been developed which can accurately identify anomalies on the Moon, the unsupervised ML framework could be applied to other planetary bodies. A logical next step would be the planet Mars. With the geological evidence for a more habitable phase in its geologic past, Mars could be considered the most likely place in the inner solar system after Earth to be a center for the formation of life. This argument is made more compelling by the recent evidence of a potential biosignature in rocks at Jezero Crater found using NASA’s Perseverance rover.

If Mars is the most likely place outside Earth in the inner solar system to have indigenous non-terrestrial life, it also follows that it would be the most likely place to find non-terrestrial intelligence. This is not to say that intelligent life is likely to have evolved on ancient Mars, but a planet with life is more likely to have intelligence evolve than a planet with no life from the start. Alternatively, the potential past habitability of Mars also makes it a likely place for non-indigenous intelligent life as a target for exploration, prospecting, or even colonization. This point is exemplified by aliens from Earth (i.e., Homo sapiens) that currently have plans to explore and possibly colonize the red planet.

Developing an unsupervised ML model to reconstruct Mars geology would not be drastically different from developing an unsupervised ML model for lunar geology. The main difference is that the terrain and range of geologic features on Mars is greater and more complex. The Moon’s geology has been largely shaped by impact events and volcanic eruptions. Most of the Moon’s geologic features are related to these two processes. Volcanic activity and impact events have played a major role in Mars’s history, but so has wind, running water, glaciers, ice sheets, and ground ice. This make the geology of Mars much more complex than the Moon, so it will be more difficult to train a model to identify anomalies on Mars just because of the greater diversity of features.

After the Moon and Mars, the next logical place in my opinion would be icy, ocean-bearing moons in the outer solar system like Jupiter’s moon Europa or Saturn’s moon Enceladus. Using the same logic I used for Mars, icy moons with potentially habitable subsurface oceans are the most likely places to host non-terrestrial life after Mars and are there also the most likely place to find non-terrestrial intelligence. This non-terrestrial intelligence could be indigenous the icy moon or take the form of off-world visitors or colonists.

An unsupervised ML approach to technosignature detection on the surface of Europa or Enceladus is particularly helpful. This is because of the highly speculative nature of of a technologically advanced civilization that developed in the subsurface ocean of an icy moon and what form its technology would take. For example, such a civilization would not be able to use fire (i.e., combustion), which is directly or indirectly the basis of much of our civilization’s advanced technology. The evolutionary relationship between human civilization and fire is explored in depth in Stephen J. Pyne’s book The Pyrocene.

This has implications. Would we expect the same type of technological structures that one might expect from an originally land-dwelling civilization that can use combustion-based technology? This is a fascinating problem but also one that is unlikely to be solved in the time limit imposed by the average research grant. Focusing on the natural geology and flagging structures that don’t fit natural patterns saves time and allows us to avoid the pitfalls of prior assumptions.

In some ways, the geology of outer solar system icy moons is similar to that of Earth’s Moon. Impact events and volcanism, albeit cryovolcanism, where the lava is liquid water instead of molten rock, have both played a role in the geologic history of icy outer solar system moons. In other ways, the geology of icy moons is wildly different. For example, tectonic processes, including faulting and rifting, have played a significant role in in the geological evolution of the surface of Europa and possibly other geologically active icy moons.

This makes Europa and similar icy moons less like the Moon or Mars geologically and more like Earth, where geology is dominated by plate tectonics, where the crust is divided between tectonic “plates” with most of the active geology on Earth (volcanic eruptions, earthquakes, etc.) happens at the plate margins where the plates are in contact with each other. The plate tectonics of Earth is unique in the solar system and not found on other planetary bodies in exact replication. Nonetheless, many parallels are found between tectonic processes on Earth and Europa, including plate subduction.

This means that the geologic features identified as natural could be different than those identified on the Moon or Mars. Thus, features that would be anomalies on the Moon or Mars would not be anomalies on Europa or Enceladus. Making a ML model trained on the geology of each body would therefore be a complex endeavor, but it would also expand our search, not just for technosignatures but also weird undiscovered planetary phenomena and resources (water, minerals, etc.) for future astronauts and space settlers.

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Although Enceladus is a common astrobiological target, our ability to predict its potential habitability is limited by the fact that it is not clear what is driving the current geologic activity on Enceladus.

To explore this topic, I am working with my collaborator to create geologic maps of Enceladus and computer models that predict tidal stress to investigate the role that polar wander stress could have played in the formation of Enceladus’s active geologic features. In this update, I show some of the preliminary results of my part of the project. This project is still ongoing but model results so far suggest that true polar wander could play a role in Enceladus’s surface geology and very similar geology on Uranus’s moon Miranda. This project adds to our understanding how icy moons work and the number of possible habitable ocean worlds in the solar system and beyond.

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The most famous example of a cosmic event influencing life on Earth is the asteroid that hit Earth around 66 million years ago. The asteroid collided with Earth and formed Chicxulub Crater in what is now Yucatan Peninsula. In the popular version of the story, the asteroid also wiped out the non-avian dinosaurs, triggering the fifth mass extinction.

Based the impact crater at Chicxulub, the event is supported by a clay layer rich in iridium, a metal rare on Earth’s surface but common in asteroids, dating to about 66 million years ago. This iridium-rich layer now defines the boundary between the Mesozoic (i.e., age of the dinosaurs or reptiles) and Cenozoic (i.e., age of mammals) eras

Although this is appealing for its simplicity, the actual story is more complex. At the time that the asteroid hit, enormous volcanic eruptions had been ongoing for 700,000 years. These eruptions formed Deccan Traps, an enormous layer basalt in modern-day India.

The resulting environmental disturbances from the Deccan Traps eruptions had already made life on Earth miserable for the dinosaurs. The asteroid strike was just the proverbial straw that broke the hadrosaur’s back (I had to adapt the cliche for our purposes). Interestingly enough, the recent discovery of the Nadir crater in West Africa indicates there was another asteroid collision around the same time. About 66 million years ago was a bad time to be on Earth, apparently.

There are also lesser known impact events that may have influenced the evolution of life. One such event is significant to me since it is relevant to research I did as a graduate student a the University of North Dakota. While a graduate research assistant, our team, led by my advisor, used the NASA Infrared Telescope Facility (IRTF) to observe asteroids in the Massalia asteroid family.

An asteroid family is a group of related asteroids which are fragments of a larger protoplanet that was destroyed in a catastrophic collision. The Massalia asteroids are one of the proposed sources for the L-chondrite meteorites.

Most meteorites that fall to Earth are chunks of iron, remnants of the metal cores of large protoplanets that got destroyed in catastrophic collisions. L-chondrites are classified as ordinary chondrite meteorites and they are the most common non-iron meteorites to fall to Earth. All L-chondrite meteorites show mineralogical evidence of having been through a catastrophic collision about 500 million years ago.

Our goal was determine the composition of Massalia family asteroids based on spectroscopy, or what wavelengths of light are absorbed or reflected by minerals on the asteroid’s surface. This was to test the hypothesis that one or more of the Massalia asteroids are the source of the L-chondrite meteorites.

How does this connect to life on Earth? Interestingly, there is a high concentration of fossil L-chondrite meteorites in limestone layers that formed about 470-480 million years ago. This was during a period in Earth’s geologic history known as the Ordovician (485-440 million years ago or Ma).

The Ordovician Period experienced an explosion in biodiversity known as the Great Ordovician Biodiversification Event (GOBE), beginning around 480 million years ago and lasting 40 million years. During this time, there was a great increase in the diversity of marine life where the Cambrian Fauna, such as trilobites, were replaced by the Paleozoic Fauna, including star fish, corals, and cephalopods. This change in biodiversity also set the stage for life evolving into the forms that we know today.

As Steven Gould would tell you, often periods of environmental stress will drive the evolution of new species because of the need to adapt to harsh conditions. Could it be that the environmental pressures created by minor asteroid impacts contributed to the GOBE? Could we in part owe the current state of life on Earth and L-chondrite meteorites both to a cosmic event that happened 480 million years ago? I am not saying that the break up of the L-chondrite parent body caused the GOBE, but it is certainly plausible that impacts by fragments of the L-chondrite parent body influenced conditions on Earth at that time.

While asteroid impacts and comet strikes affect life on Earth, there is also evidence that the frequency asteroid and comet strikes may be affected by galactic forces. A recent paper found evidence from a correlation between hydrogen density in the galactic disk and oxygen isotopes in zircon crystals that the evolution of Earth’s crust could be influenced by Earth’s solar system passing through regions of the galactic disk that are especially dense in matter during the sun’s orbit around the center of the galaxy.

Why in the universe would this be related? When the sun passes through dense parts of the galactic disk, gravitational perturbations from said matter can cause the orbits of bodies near the edge of the solar system, mostly comet-like objects in what is called the Oort Cloud, to be altered so they collide with Earth. An increase in the frequency of impacts on Earth by incoming comets would affect the evolution of the crust because they would add thermal energy to the crust and thus what rocks form. In this way, galactic processes may be written into Earth’s geology.

Earth’s geology is not isolated from the wider galaxy, but appears to be directly influenced by galactic events and processes. Could the same be said of life? The evolution of life has clearly been influenced by previous impact events, so it is only logical to conclude the life on Earth is also shaped to some degree by galactic processes.

The effects of the gravity of passing star clusters on the evolution of life on Earth is likely to be minimal, except over very large timescales. On the other hand, it is possible that life my one day have a more significant influence on the galaxy. We already know that life is a driving force in Earth’s geology. If technological life on Earth does spread beyond this planet, it may that one day life will also be a driving force in the solar system and eventually the galaxy. This may never happen, but as we learn more about how our planet is connected to the cosmos, we should get used to thinking of our planetary system and the universe as being interconnected.

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The science funding situation has only gotten more precarious since then. This inspired me to consider future possibilities for funding science in a more sustainable way and experiment with it myself, including crowdsourced through the Substack platform. To explain why this makes sense, let me provide a quick background to science funding in the United States.

Today, there are essentially three common ways to fund scientific research. These ways include government funding, usually for universities, private research institutes dependent on federal grants, or government agencies, for-profit startups, and private donation-based funding.

In the United States, most federally funded research is supported through government agencies or departments like NASA, the National Science Foundation, and the Department of Energy. The main advantage with federal funding is that it is ideal for research that does not have an immediate business case, like a robotic mission to Europa. The primary drawback of federal funding is that it is competitive and how much funding any research project receives depends on whether it aligns with the policy goals of a particular administration or government.

For-profit startups are a good approach when the goal of the research is to produce a product, such as an AI model or a new power source. The startup method provides efficiency and low cost. Just think of how SpaceX has revolutionized the launch industry by bringing down the cost of spaceflight by providing powerful and (mostly) reliable launch vehicles. The primary drawback of the startup model is that it doesn’t work if there is not an immediate profit to be made. There currently is not a business case for searching for life on Mars or sending quadcopters to Titan.

Another more philosophical problem with relying too heavily on a for-profit approach to funding space science is that thinking of everything in terms of profit tends to take away from the spirit of exploration and appreciation of the intrinsic value of science that fundamental research should inspire. We explore the universe because it is inherently worth exploring not because of what we can economically gain from it.

The third source of funding is through large donations to nonprofit organizations that conduct scientific research. Most major museums like the American Museum of Natural History, individual research fellowships like the Heising-Simons Foundation’s 51 Pegasi b postdoctoral fellowship, and certain prestigious research institutions like Carnegie Science are funded this way.

Donors tend to give on principle meaning that projects do not need to have an immediate financial benefit or relevance to the current space policy goals of the day. They just need to align with the goals and values of the donor. The main drawback of this approach is that the values and goals of the donor can heavily sway what kind of research is done.

These three approaches to funding all have their strengths, but with each of them something is missing. Some research projects may be vital, but not large enough for federal funding, not exciting enough for a startup, and too niche for large donors to support. These include projects which may only cost a few thousand dollars to cover lab or field equipment and are studying something interesting but commonplace like the distribution of wild bees in the California desert.

Besides these three ways of funding research is crowdsourced funding. Donations are still involved, but unlike with institutions like Carnegie Science, donations tend to be small and the number of donors is much larger so a single donor will not have quite as much influence. A recent example of crowdfunded research in the space sector is the Planetary Society’s successful LightSail project to build a functioning spacecraft powered by light pressure propulsion, aka, solar sails. Functional solar sails have the potential to make spaceflight cheaper by reducing the need for backup fuel. It was funded entirely by donations from individual Planetary Society members.

While crowdfunding is unlikely to fund a multi-billion dollar mission to Uranus, there is potential for crowdsourced funding to support research projects that are vital but too small to receive federal funding. Crowdsourced funding can also support vital research which is still too commonplace to interest venture capitalists, who typically only support projects that they perceive as groundbreaking or sufficiently ambitious.

Another advantage of crowdfunded research is the potential for public outreach. If researchers are seeking to convince members of the educated public to support them, this forces them to develop skills in science communication. Scientific research is meant to be shared with the world and the best way to show the value of science is to directly communicate its significance to the public and invite them to be part of it.

This combination of public engagement and possibility to fund small to medium level projects is why I chose Substack for this experiment. Instead of asking for crowdfunding for specific projects, my goals is to use the Substack model and publish a weekly newsletter to keep subscribers updated on my ongoing research projects. This will both provide stability through constant revenue from subscriptions and a natural channel for science communication.

Most of these weekly newsletters are and will continue to be free, alternating between commentary on the latest science discoveries, proposals for exciting research ideas, and philosophical reflections on the value of science and exploration. By sharing my research results through regular newsletters, I seek to build a relationship with my readers so that they feel connected with my work enough to want to subscribe. Science after all is for everyone and everyone should be able support the scientific investigations that excite them.

The newsletters focusing specifically on updates to my current research projects, however, will be for my paid subscribers. These newsletters will come at least once a month, so that supporters know my monthly progress. I will also provide my supporters with any published abstracts, preprints, or datasets from my research as far as I am permitted to do so. In this sense, my supporters are paying for the newsletter updates on the research which they have agreed to support. The revenue from the paid subscriptions of this newsletter will go to financially cover the costs of the research, including software, travel to conferences, open access paper submissions, laboratory space, and the equivalent of a research stipend.

A project I specifically have in mind to fund through Substack is to use machine learning to compare the mysterious coronae (regions of concentric ridges) on Miranda and Venus to determine if they are truly analogous features, which has significant implications for icy moon geology and habitability. Since coronae have been suggested to be related to plate subduction, Venus-like coronae on Miranda could indicate a way that vital nutrients could get into the proposed subsurface ocean of Miranda, increasing the chances that the tiny moon, and icy moons like it, could support life.

Why would readers support my work? That is a fair question. My credibility comes from the fact that I have a successful track record as a researcher. I have spent years doing planetary science work, during which I was an intern at Jet Propulsion Laboratory for two years, earned my PhD, and have two papers published in peer-reviewed journals in the last 18 months. I know how to do research, collaborate with colleagues and get work published, which at least makes me qualified for a more conventional research position.

The intended outcome of this experiment is to make decentralized approaches to science funding more commonplace and build trust between scientists doing research and non-scientists who want to support science and discovery. If you are excited about planetary exploration or just want to see science become more open and democratic, I would be honored to have you join me and subscribe. You won’t just be supporting a project but helping build a new model of science is done. Let’s build a better future together.

Thank you for reading my Substack! If you like what you read, feel free to share or subscribe and thank you again if you already have.

If you would like to support planetary science research, you can become a paid subscriber and double thanks if you already have.

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Miranda’s enigmatic surface was first observed by the Voyager II spacecraft during its visit of the Uranus system in 1986, revealing that Miranda had bizarre regions of concentric ridges, now called coronae. Ariel was also revealed to have an unusual surface with ridges, smooth plains, and even possible cryovolcanism, volcanoes where the lava is water instead of molten rock.

Recent studies using spectroscopy, looking at what wavelengths or colors of light are absorbed or reflected by a material to determine its composition, have also revealed that Miranda may have short-lived ammonia compounds on its surface which would have to come from a subsurface liquid water ocean. This leads to a question. Could Miranda have plumes as well? So far plumes have not been detected at Miranda, but they were also not initially detected at Enceladus either.

Short of sending another spacecraft to explore the Uranus system, there is a way to try to answer this question. Large telescopes such as the ALMA, the Keck Observatory and the Hubble Space Telescope have been used to observe or search for plumes on icy moons, particularly Jupiter’s moon Europa.

One problem with Miranda having plume eruptions is that there is not an associated debris ring. If water ice particles are being spewed out of Miranda, they would be expected to collect in a ring around Uranus near Miranda’s orbit like with Enceladus and Saturn’s E-ring. This has not been observed at Miranda’s orbit at Uranus, which might indicate that there is not plume activity on Miranda.

On the other hand, there is also reason to suspect plume eruptions could be happening on Jupiter’s moon Europa, yet no debris rings are forming in Europa’s orbit. In Europa’s case, this might be because the plume eruptions are not energetic enough for the ice particles to escape Europa’s gravity. Europa is a relatively large icy moon (diameter = 3100 km or 1900 miles).

In the case of Miranda, which is considerably smaller (diameter ~ 470 km or 290 miles), it could be due to the eruptions on Miranda being primarily gas and having relatively few water ice particles. This could be due to a greater abundance of gases dissolved in Miranda’s subsurface ocean, though this is pure speculation at this point.

There is currently no evidence that plume eruptions are happening at Miranda, but we will not know unless we take look and the discovery would be very significant. This could be done using a spectrograph on one of the major telescopes, such as the Keck NIRSPEC instrument or the one on the James Webb Space Telescope to search for the spectroscopic signature which would indicate the presence of water vapor coming out of Miranda.

If observations of Miranda confirm the presence of plumes, it would mean that Miranda is still warm enough to have a subsurface ocean. This would mean that whatever heated up Miranda happened very recently in geologic time, confirming that Miranda has had a very interesting history.

In fact, computer models of the orbits of the Uranian moons predict they went through a phase of rapid orbital evolution. The shapes of their orbits changed, resulting in gravitational interactions between the other moons and Uranus which caused Miranda to become physically stretched back and forth, producing heat, like heat generated by the bending of a rubber band, to melt part Miranda’s ice layer about 500 million years ago. This would have been just yesterday in geologic terms.

Also, samples of Enceladus’s plumes taken by the Cassini spacecraft support the existence of possible hydrothermal vents on its ocean floor, potential habitats for early life in Earth’s oceans. Miranda may not have hydrothermal vents on its ocean floor, but the presence of plumes would be one more indicator that Miranda could be another Enceladus in that regard.

The discovery that there are not plumes on Miranda would also be interesting since this would reveal that not every geologically active icy moon has plumes. This would add to the known variety of ocean worlds and to our understanding of which are likely to support life, since a subsurface ocean by itself does not mean life.

Furthermore, discovering two similarly sized moons with active plume eruptions and subsurface oceans in the solar system would suggest that such environments could be common in other stars systems as well. This would give us a better idea of what icy bodies look like across the galaxy.

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In 2018, the OSIRIS REx spacecraft visited the 500 m (~1600 foot) diameter asteroid (101955) Bennu and returned samples to Earth on September 24, 2023. Chemical analysis of the sample from Bennu provides evidence of hydrothermal deposits from the interaction between silicate minerals and flowing hot liquid water.

To be clear, this does not mean that there was ever hot liquid water within the ~1600 foot diameter asteroid Bennu. With a diameter a little greater than the height of the Empire State Building, Bennu itself is much too small to have ever sustained high enough internal temperatures to support liquid water in its interior. On the other hand, Bennu is likely a fragment of a larger protoplanet about 100-160 km (~60-90 miles) in diameter that was destroyed in a catastrophic collision. Conditions could have been right for hydrothermal activity when the Bennu parent body had recently formed and still had a relatively warm interior from the decay of radioactive isotopes.

For the sake of clarity, I use the term protoplanet to refer to planetary bodies that formed from the direct accretion of material within the primordial accretion disk that existed around the infant sun when the solar system was still forming. “Asteroid” refers to any rocky body that is above a certain size threshold that is not large enough to be a planet.

Could the Bennu parent body have had the right thermal and chemical conditions for liquid water in its interior? A recent paper analyzed boulders on the surface of Bennu, showing evidence from rock texture the the boulder material was originally deposited in running water in the interior of the parent body. Rocks made from sediment that is deposited by flowing water before being lithified are called sedimentary rocks. They are very common on Earth, including sandstone and shale. Sedimentary rock has also been found on Mars.

The possibility that sedimentary rock formed in an environment with running water within a 100-150 km protoplanet is surprising because it suggests that you can get hydrothermal activity in very small protoplanets. Beyond minerals associated with wet environments, evidence of actual surface hydrothermal activity has only been found on one asteroid, the protoplanet Ceres, which is not directly related to the asteroid Bennu.

On the other hand, there are other asteroids of comparable size to that predicted for the Bennu parent body, but a little larger (diameter = ~300-350 km), that have a Ceres-like reflectance spectrum. This means the colors absorbed or reflected from these asteroids indicate that they have minerals that were chemically altered by liquid water on their surfaces, a tall-tale sign of hydrothermal activity.

If a 150 km diameter protoplanet could have had near-surface hydrothermal activity, why not 300 diameter protoplanet? Widespread hydrothermal activity on early protoplanets has implications the abundance of environments where life could have formed in the early solar system.

A common hypothesis is that life formed on Earth in oceanic hydrothermal vents. This is why the possibility of hydrothermal vents on the ocean floors of the subsurface oceans of icy moons are so important in the search for life beyond Earth. If hydrothermal conditions were also present in 100 km scale asteroids, that means there were thousands of worlds in the early solar system with the potential for life to form.

Is there any way to test this possibility? There are computer models that can simulate the internal temperature the be expected for a planetary body, based on assumptions about the size and thermal properties of internal layers within the body. Also, there are computer models, like PHREEQC, that can simulate what minerals would be stable within a given environment based on temperature and pressure ranges.

For example, water ice (a mineral) only exists within a certain range of temperatures on Earth’s surface, specifically when the temperature is below 0 degrees Celsius, otherwise it melts or sublimates. The stability range for liquid water by contrast is 0-100 degrees Celsius at an atmospheric pressure of about 1 bar.

One way to predict whether Bennu’s parent body could support hot liquid water with dissolved salts (a hydrothermal brine solution) despite its small size would be to generate models predicting the internal temperature of asteroids or protoplanets the size of the Bennu parent body (D =100-160 km) up to Ceres-sized (D = 1000 km). Once these thermal models have been made, geochemical models can be made predicting the temperature and pressure range within which hydrothermal brine solutions are stable.

Once we have made both the thermal models predicting internal temperatures of asteroids and protoplanets 100-1000 km in diameter and geochemical models predicting the pressure and temperature range within which hydrothermal solutions are stable, we can map the geochemical models showing where hydrothermal solutions are stable onto models of internal asteroid temperature to see if there is an overlap between the temperature and pressure range for stability of hydrothermal solutions and the predicted internal temperature asteroids or protoplanets of the required size range. If it can be shown that hydrothermal solutions are stable at the expected temperatures in the near-surface of a 100 km scale asteroid, this would not prove that there was near-surface hydrothermal activity on 100 km diameter asteroids, but it would support that possibility.

Whether this modeling exercise supports hydrothermal activity on the Bennu parent body or not, the results would very significant. They would tell us more about how planets work and also how common habitable pockets in protoplanets were in the primordial solar system and in other recently formed solar systems across the galaxy. If life could form in Bennu’s parent body, it could form anywhere.

Thank you for reading my Substack! If you like what you read, feel free to share or subscribe and thank you again if you already have.

If you would like to support planetary science research, you can become a paid subscriber and double thanks if you already have.

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