Once home to oceans, rivers, and lakes, Mars was a much wetter world billions of years ago — but what happened to all that water?
A pair of UT Austin grad students uncovered a missing piece of the puzzle: the time it took water to seep from the surface deep into the Martian crust.
Mars’ Mysterious Water Cycle
Billions of years ago, rivers and lakes flowed across the surface of Mars. But scientists have long struggled to understand exactly how the Red Planet’s ancient water cycle worked.
Now, two graduate students from The University of Texas at Austin have helped fill in a major missing piece. Their research sheds new light on what happened to Mars’ surface water—and how much of it may still be hiding underground.
Using computer models, students Mohammad Afzal Shadab and Eric Hiatt estimated how long it would have taken water to seep from the Martian surface down to deep underground aquifers. They found that on early Mars, this process could have taken between 50 and 200 years. By comparison, water on Earth can travel to the water table in just a few days.
Their findings, published in Geophysical Research Letters, help solve a crucial mystery about how Mars lost its once-abundant water.
Hidden Depths of Martian Water
The team also discovered that the amount of water seeping below the surface was likely enormous—enough to cover the entire planet in at least 300 feet of water. That suggests a significant share of Mars’ total water may not have escaped to space after all, but instead sank into the ground and stayed there.
This insight helps researchers build a clearer picture of Mars’ full water cycle. Shadab, now a postdoctoral researcher at Princeton University, explained that knowing how water moved through the planet’s crust can help estimate how much was available to evaporate, rain back down, and fill ancient lakes and oceans.
“We want to implement this into [an integrated model] of how the water and land evolved together over millions of years to the present state,” said Shadab, who was the study’s lead author. “That will bring us very close to answering what happened to the water on Mars.”
Mars: From Wet to Dry
Today, Mars is largely dry, at least at the surface. But 3 to 4 billion years ago — at around the time that life was getting started on Earth — oceans, lakes, and rivers carved valleys through Mars’ mountains and craters and imprinted shorelines in the rocky surface.
Ultimately, Mars’ water took a different path from Earth’s. Most of it is now either locked in the crust or was lost to space along with Mars’ atmosphere. Understanding how much water was available near the surface could help scientists determine whether it was in the right places long enough to create the chemical ingredients needed for life.
A Dry and Final Destination
The new findings add to an alternative picture of early Mars in which there was little water going back into the atmosphere through evaporation and raining down to refill oceans, lakes and rivers — as it would have on Earth — said coauthor Hiatt, who recently graduated with a doctoral degree from UT Jackson School of Geosciences.
“The way I think about early Mars is that any surface water you had, any oceans or large standing lakes, were very ephemeral,” he said. “Once water got into the ground on Mars, it was as good as gone. That water was never coming back out.”
Hope for Future Exploration
The researchers said that the findings are not all bad news for potential life on Mars. If nothing else, the water seeping into the crust wasn’t being lost to space, Hiatt said. That knowledge could one day be important for future explorers looking for buried water resources to sustain a settlement on the Red Planet.
Reference: “Infiltration Dynamics on Early Mars: Geomorphic, Climatic, and Water Storage Implications” by Mohammad Afzal Shadab, Eric Hiatt, Rickbir Singh Bahia, Eleni V. Bohacek, Vilmos Steinmann and Marc Andre Hesse, 25 April 2025, Geophysical Research Letters.
DOI: 10.1029/2024GL111939
Shadab and Hiatt’s research was supported by a Blue Sky grant from the University of Texas Institute for Geophysics, a research unit of the Jackson School, and grants from UT Austin’s Center for Planetary Systems Habitability and NASA.
The work was conducted while Shadab was earning a doctoral degree from the Oden Institute for Computational Engineering and Sciences at UT Austin. Other coauthors include Rickbir Bahia and Eleni Bohacek from the European Space Agency (now at UK Space Agency), Vilmos Steinmann from the Eotvos Lorand University in Hungary, and Professor Marc Hesse from the Jackson School’s Department of Earth and Planetary Sciences at UT Austin.
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