When we gaze up at the night sky, billions of possible homes for alien life are looking back. But how do scientists determine which planets might actually be home to living creatures? The answer has to do with something strangely familiar: geography. In the same way Earth’s mountains, oceans and valleys narrate the story of our planet’s history, these dead worlds’ geographical features help tell whether or not they could have supported life as we know it on Earth.
It’s not just little green aliens waving at us from a distant planet that scientists are looking for. It’s not life itself that they’re after, but the conditions that make life possible — the perfect combination of ingredients. And it’s a finding that, as it happens, holds tantalizing information about water, atmosphere, temperature and chemistry inside an exoplanet. Each crater, each ice cap, even each volcanic region is a chapter in the tale that can help us address one of humanity’s most profound questions: Are we alone in the universe?
Why Geography Matters in Quest for Life
Geography isn’t all about maps and mountains. It’s about learning how a planet operates — its weather, what it’s made of and the forces that shape its landscape. On Earth, it’s geography that dictates where life can thrive. Deserts, rainforests, deep ocean floors and frozen tundras all present different types of life that have adapted to each of these distinctive locales.
Another planet would be the same. When scientists explore the geography of a planet, they are searching for evidence that liquid water may have once or still does flow across the surface. They are trying to determine whether the planet is shielded from deadly radiation. They’re gauging whether temperatures are within a range that would allow the chemical reactions required for life. All of these clues derive from the science of studying the land itself.
Picture it this way: if you stumbled onto any foreign island on Earth, there would be a lot you could figure out just by looking around. Sandy beaches suggest ocean water. Plants are fresh water and soil. Ice means cold temperatures. The same logic applies when scientists study planets millions of miles away.
Water’s Fingerprints Written in Stone
At least, that’s how we understand it. Water is life’s most essential ingredient. Anything that lives on earth is going to need water or it won’t survive. That’s why scientists get giddy when they see the kind of geographic features that might hint at water lurking in someone’s past or present.
Ancient River Valleys
On Mars, some of the best evidence for ancient water is on display. Orbiters have taken pictures of dried-up river channels, lake beds and delta formations that bear a strong resemblance to Earth’s river system. These winding valleys chiseled into Martian rock were not etched by wind or lava — they were created, over billions of years, by flowing water.
And its geography speaks volumes: Mars used to have a denser atmosphere and warmer temperatures. Rivers tumbled from high to low, carving deep channels in the stone. Some of those channels are thousands of miles long and hundreds of feet deep. This is not pure wishful thinking — it is written in the landscape.
Smooth Plains and Layered Deposits
Planitiae on Mars, the smooth flat places that were likely ocean floors in an earlier epoch. Researchers discovered shoreline-like features at similar elevations, providing evidence that an ocean once spread across a large part of the northern hemisphere. On the other hand, layered formations of sedimentary rock—stone arranged in distinct layers—are signs that materials gently settled out into standing water like sediment layers at the bottom of lakes on Earth.
Ice Beneath the Surface
Geography also reveals hidden water. Radar instruments are the tools scientists use to see beneath surfaces of other planets. The rovers have found huge ice deposits buried beneath dust and rock on Mars. One of Jupiter’s moons, Europa has an extremely smooth shell of cracked ice that has led scientists to speculate there is a liquid ocean below — possibly containing more water than all the oceans on Earth combined.
Europa’s surface ridges and cracks create some striking patterns. Those aren’t random — they’re from the tidal forces of Jupiter’s gravity warping the moon’s interior, an action that allows the subsurface ocean to flow despite the icy environment of outer space. The geography literally gestures toward hidden water.
Volcanoes: More than Nature’s Fury; a Life Support System on Earth
Volcanoes might seem the enemy of a habitable planet, but they could be responsible for making planets more Earth-like. The study of volcanic geography allows scientists to spot worlds with living, active geological systems — an indication that a planet hasn’t yet become entirely “dead” inside.
Heat and Chemistry
The volcanic outgassing of heat and chemicals from a planet’s interior is fundamental for the reason why Earth’s atmosphere was populated with oxygen, thus also for life as we know it. This warmth has the power to melt ice, producing liquid water in unexpected locations. Those chemicals — sulfur, phosphorus and others — are nutrients life needs to grow and reproduce.
On Earth, some of the hardiest forms of life congregate around volcanic vents on the ocean floor. These “extremophiles” don’t require sunlight; they extract energy from chemicals emanating out of the vents. If similar volcanism occurs on other worlds, particularly beneath icy coverings, life could flourish in those hidden hot spots.
Enceladus and Io: Volcanic Worlds
Another of Saturn’s moons, Enceladus, has evidence for incredible eruptions. But in place of magma, its volcanoes fire ice and water vapor up into space through huge geysers from its southern pole. This material has been analyzed to contain organic molecules, which are the basis for life as we know it.
Jupiter’s moon Io is the most volcanically active object in our solar system. Though its surface is too hostile to support life as we know it, studying Io can help scientists learn how geological activity fuels other worlds. If a planet or moon displays volcanic geography, it probably has internal heat — and where there’s heat, there may be liquid water and chemical energy for life.
Hints from the Surface Features in the Atmosphere
You can’t see the atmosphere of a planet, but you can see how it affects its geography. Surface properties show whether or not the planet had—or has—an atmosphere that could support life.
Wind-Carved Landscapes
Giant dust storms on Mars produce large wind-sculpted features, also known as yardangs, which are ridges of rock carved by windblown sand and dust. Dunes are shaped in particular patterns based on the force and direction of the wind. These landforms can clue scientists in to atmospheric pressure, wind patterns, and seasonal variation.
A thick atmosphere not only shields surfaces from harmful radiation, but also helps to moderate temperatures. It can retain heat (like a greenhouse) or ferry water vapor to create rain. By understanding how wind has sculpted the surface of a planet over millions of years, scientists can help determine whether its atmosphere could have been capable of sustaining liquid water and stable climates.
Weathering and Erosion Patterns
Here on Earth, rock weathers and erodes through rain, wind and ice. Various weathering processes form various landforms. This rounded, smooth shape is created through chemical weathering (i.e. when water reacts with minerals) of the rocks. Crater counts suggest it is an ancient surface, and the terrain — which is jagged and broken due to physical weathering (such as temperature changes or ice) — looks battered.
Scientists see these patterns on other planets, they know what processes happened. Smooth, rounded rocks on Mars? Probably tumbled by flowing water. Fractured boulders? Temperature swings or freeze-thaw cycles. Each of those features represents a clue about past environmental conditions.
Magnetic Fields and Protective Geography
Here’s one line of reasoning that few stop to consider: A planet’s magnetic field is essential for life, and geography can help determine whether a world does have one.
The Earth’s magnetic field is like an invisible armor that protects us by shielding us from harmful solar rays and preventing our atmosphere from being blown away by the solar wind. Mars probably had something like a magnetic field, but it dissipated billions of years in the past. Without such a shield, solar wind whittled away Mars’s atmosphere slowly over time, gradually siphoning off the planet’s surface water and turning it into the cold, dry place we see today.
Magnetic Minerals in Rocks
Rocks are one way that scientists can find remnants of ancient magnetic fields. As molten volcanic rock cools, magnetic minerals inside it become magnetized in the direction of the planet’s magnetic field, like little compass needles frozen in stone. By studying these “fossil magnetism” records in Martian meteorites as well as surface rocks, scientists reconstructed Mars’s magnetic history.
There are also some features of the geography that give the magnetic field strength. For instance, areas shielded by local magnetic fields could be less eroded by solar wind. This in turn leads to variations in surface weathering patterns — geographical evidence of invisible magnetic processes.
Planetary Geographies: The Hits and the Misses
When it comes to life-harboring real estate, not all planetary geographies are created equal. Let’s see what scientists have discovered by studying alternate worlds.
Thus, this comparison demonstrates that the mere presence of certain geographical features is not sufficient to gauge well a planet’s habitability status. While Mars had proper signs, it lost its atmosphere, Europa’s ocean is hidden and covered with an unknown ice layer and two massive sources of radiation, and Venus, on the other hand, became filled with runaway greenhouse gas. One proves that one can make assumptions based on the planet’s geography but cannot know for sure what has transpired on a planet or moon. Other factors, such as makeup and elements present in the atmosphere and in quantities not easily obtainable in graphs and charts. Thus, other factors besides geography need to be considered.
Reading Planets as Books: Crater Geography
Counting Craters
A surface cratered like the moon is old and geologically dead. The craters built up over billions of years without other geologic processes wiping them away. A small number of craters equals active geology—volcanism, tectonic action, or erosion—routinely resurfaces the planet and wipes out evidence of impacts.
Regarding the surface composition and age: Europa doesn’t have a lot of craters, meaning that it’s relatively young (geologically)—somewhere between 40-90 million years old. This indicates the internal ocean recharges the ice shell continuously, strong proof that the ocean is alive and well today.
Crater Ejecta Patterns
Patterns in debris ejected during impacts show surface composition. On Mars, some craters are surrounded by “splash patterns” that hint that they collided with ice or mud, rather than dry rock. These geographical signatures represent possible locations of buried water ice just beneath the surface — targets for future exploration.
Chemical Signatures in Geographical Features
Everything will be colored differently by different minerals. By looking for variations of color and composition across a geography with the help of spectroscopy, scientists can tell what chemicals are on a planet’s surface.
Oxidized Iron on Mars
Mars is red because its rusty surface is made of oxidized iron. Rust is formed when iron and oxygen combine with water. The locations of different iron-bearing minerals give scientists evidence for past watery environments. Other regions have minerals that are known to precipitate only from neutral or even slightly acidic water — something more amicable for life than the acid baths in evidence elsewhere.
Salt Deposits
Crusty, white deposits found in Martian craters and valleys are salt left behind as ancient water evaporated — akin to the salt flats that form on Earth. These were ancient lakes and seas. Some salts, including perchlorates, are capable of preventing water from freezing in sub-freezing temperatures, so some brackish pockets where microbial life could survive today may be able to persist.
Tectonics: A Product of a Living Planet
The movement of enormous crustal plates, known as plate tectonics, is essential for life on Earth. It is a recycling system for chemicals, has the ability to regulate atmospheric carbon dioxide and generates lots of different places to live. The geologic evidence of tectonic action that makes this possible, suggests a planet has the kind of complicated internal business it might need for life.
Mountain Ranges and Rift Valleys
Here on Earth, mountain ranges develop where tectonic plates smash into each other, and rift valleys gape open where they pull away from one another. On other planets, scientists search for comparable geological features. Venus displays potential tectonic activity in the form of mountain belts and volcanic areas. Though Venus is too hot for life today, knowledge of its geology enables scientists to estimate which exoplanets might be experiencing active plate tectonics.
There is no evidence that Mars currently has any plate tectonics, however some of its surface features hint at the possibility it might have experienced a brief episode of intense tectonic activity early on in its history. The giant canyon system Valles Marineris could have formed in part by stretching of the crust.
The Geography of Planets beyond Our Solar System: What We’re Learning
We cannot yet map in detail the geography of planets around other stars, but scientists use indirect means to picture their surfaces.
Transit Spectroscopy
When an exoplanet transits in front of its star, scientists study how starlight is filtered through the planet’s atmosphere. Each molecule absorbs certain wavelengths of light, and the set of absorbed light forms a “fingerprint.” This doesn’t map geography directly, but reveals atmospheric chemistry shaped by surface processes.
A planet containing both oxygen and methane is a sign of potential life; because these gases usually destroy one another rapidly — something (such as living organisms) must be continually producing them. The geography of the planet determines which gases its atmosphere can contain and to what extent surface processes release chemicals into the air.
Future Observations
The next generation of telescopes will just start to be able to see the massive geological features on close-in exoplanets. By how different surfaces reflect light, they hope to be able to distinguish between continents versus oceans. Continents and oceans could be evidence for water, weather cycles and perhaps plate tectonics — all good news for habitability.
Frozen Worlds with Liquid Hearts
Among the most intriguing geographical discoveries are icy moons with subsurface oceans. These worlds defy our expectations of where life could exist.
The Ganymede, Europa, Callisto Connection
Three of the largest icy moons around Jupiter — Ganymede, Europa and Callisto — probably contain subterranean seas. Each has its own surface characteristics and shows different physics within:
Europa: Youngest terrain with chaotic landscape and intersecting ridges
Ganymede: Mixture of light and dark terrain features. Old heavily cratered regions and young, grooved terrain.
Callisto: Old, cratered surface indicates a quiet interior
The dynamic geography of Europa places it as prime candidate for life. Its surface is rapidly resurfaced, suggesting intense interaction between the ice shell and subsurface ocean — possibly carrying nutrients from the rocky ocean floor to areas that could potentially host life.
What Future Missions Will Seek
That the geography shows where life could lie buried in the soil has informed future space missions. Researchers now know precisely which geographic features are most important.
Key Targets for Exploration
Future Mars missions will:
- Explore rocks that appear to be layers of sedimentary rock patterns
- Investigate ancient lakes with clay minerals
- Search below icy deposits at protected locations
Both NASA’s Europa Clipper and ESA’s JUICE mission:
- Map Europa and Ganymede in high-detail
- Measure ice shell thickness
- Sample material from ice geysers
- Detect subsurface ocean characteristics
Learn more about NASA’s Europa Clipper mission and its search for habitable environments.
Dragonfly, a drone slated to head to Titan in the 2030s will:
- Explore diverse geographical regions
- Sample organic-rich materials
- Research the weather patterns of methane and changes to the surface
The Geography-Life Connection on Earth
It may help to consider, amid this excess of orbital research, examples from our own planetary geography about when alien life could be most revealed by surface geography. Earth’s geography dictates where and how life flourishes.
Extreme Environments
Earth’s otherworldly places — Scientists look to Earth’s most extreme environments for clues about what alien life might be like:
Antarctic Dry Valleys: Desert conditions similar to those on Mars and where bacteria live in rocks
Deep-sea Vents: Hot, dark habitats like potential conditions on Europa or Enceladus
Atacama Desert: Ultra dry habitat where life clings on without the need for much water
Acid Mine Drainage: Extremes of geomicrobiology
And each extreme environment here on Earth has something to tell scientists about which biosignatures to search for and which geographical features might hide life on other planets.
Common Questions About Planetary Geography and Alien Life
How do scientists map planetary geography on Earth?
There are several instruments that scientists employ to study the surfaces of distant planets:
- Telescopes with specialized cameras that detect different wavelengths of light
- Orbiting spacecraft that take extremely high-resolution photographs of surfaces
- Radar profiles that penetrate below the surface to reveal the location of ice or rock layers
- Spectrometers that determine minerals and chemicals by their reflected light
- Computer-generated representations of geological processes given observed features
Might life survive on worlds with geography very different from Earth’s?
Absolutely! Today scientists acknowledge that life might exist in forms and environments we cannot begin to fathom. Titan’s methane lakes, for example, might harbor life that is based on a very different chemistry than the life we know on Earth. The trick is locating stable liquid (water or something else); sources of energy; and basic chemical building blocks. Geography helps reveal the common conditions behind them no matter how alien they appear.
Why do we look to Mars’s ancient geography rather than its present geography in our search for life?
Today, the surface of Mars is cold, dry and bombarded with radiation — making it almost impossible for life to exist on its surface. But there is evidence from ancient geography that Mars had rivers, lakes and possibly oceans billions of years ago. If life existed during this wetter, warmer period, its fossils or any chemical evidence could be preserved in ancient rocks. That’s why missions target ancient lake beds and river valleys — we’re looking for past life, not present life.
How is it possible that a moon which is so distant from the Sun as Europa contains liquid water?
Europa keeps warm through a process known as “tidal heating.” The theory, the researchers explain, is that Jupiter’s tremendous gravity squishes and stretches Europa as it orbits, causing friction that heats up the moon — like bending a paperclip back and forth until it gets warm. This internal warmth prevents the subterranean ocean on Europa from freezing even though it lies outside what would be an orbit that falls into the conventional habitable zone. This non-stop flexure is what causes the grooves and ridges on Europa’s surface.
What would be the most compelling geographic sign of extraterrestrial life?
No one feature is proof that life exists, but some combinations of features become difficult to argue with. What scientists would be most interested in:
- Seasonal biological-like surface changes
- New mixtures of chemicals that organisms might be capable of generating
- Geographical patterns that appear to make sense instead of being random
- Liquid water sporadically interacting with organics
The hardest evidence would have to be if we discover multiple geochemical and geographical fingerprints that when put together indicate the action of biology rather than geology alone.
The Future of Geographic Exploration
With new technology, we can do a lot of reading of planetary geography. Future missions will deliver previously unimaginable details about faraway worlds.
Artificial Intelligence and Machine Learning
Now, AI systems can quickly analyze millions of geographical features more quickly than human scientists. These tools find patterns that humans, scanning imagery of subtle changes in crater distribution or odd mineral combinations or unlikely erosion patterns, might miss. Artificial intelligence assists with sorting through which geographic features to pursue further study.
Sample Return Missions
Even geography as read from space has its limitations. Which is why sample return missions are so essential. At the same time, returning Martian rocks to Earth permits scientists to study them with state-of-the-art laboratory equipment, revealing chemical and biological signatures that can’t be seen by spacecraft instruments. The geography does tell us where we can sample; labs tell us what those samples are.
Why This Matters to Everyone
Discovering how planetary geography tells us what life is like at its perimeters isn’t only neat science—it’s absolutely essential to the future of humanity.
Finding life elsewhere would reshape our understanding of the fundamentals of biology, chemistry and our place in the universe. It would tell us whether life in the universe is common and abundant or rare and precious. And this understanding informs our perspective of the Earth’s environment, and ultimately our responsibility to safeguard it.
Plus, figuring out which geophysical features signal habitability enables us to eventually pinpoint thousands of potentially habitable exoplanets. Among the billions of worlds in the galaxy, geography will usher us toward promising candidates — places where alien life might exist or we may go some day.
Conclusion
The rocks, ice and landscapes of worlds far from ours are talking to us. They are telling stories about water once flowing, still-rumbling volcanoes and hidden oceans that could house life. And scientists have learned to read these geographical messages, translating patterns of craters, distributions of minerals and other surface features into clues about the potential cosmic biology.
Each and every crater, valley and coastline is part of a broader world. In combination, these landscape elements form a map — not only of planetary surfaces but also of possibilities. They indicate where to look, what to look for, and why the quest for alien life is not at all hopeless. Indeed, the geography of worlds throughout our solar system and beyond indicates that life’s ingredients are surprisingly widespread. If life is as common, even so ubiquitously pervasive, then too much may remain to be seen around the moon and from it not only for us but also in us with the landscapes of other worlds that are slowly disclosing secrets one geographical hint or one biological clue at a time that tease our return.
