Imagine visiting ancient Mars—a planet not frozen and lifeless, but surprisingly mild, where rain or snow fell from the sky and rivers rushed through valleys, feeding hundreds of lakes.
A new study from geologists at the University of Colorado Boulder paints this picture of a Red Planet that was much warmer and wetter than the cold desert we know today. Their research suggests that heavy precipitation likely helped carve the vast networks of valleys and channels that shaped Mars billions of years ago—offering new evidence in a long-running scientific debate.
The team, led by Amanda Steckel, who earned her doctorate in geological sciences at CU Boulder in 2024, published their findings on April 21 in the Journal of Geophysical Research: Planets. “You could pull up Google Earth images of places like Utah, zoom out, and you’d see the similarities to Mars,” said Steckel, now at the California Institute of Technology.
The mystery of ancient water on Mars
Today, most scientists agree that some liquid water existed on Mars’ surface during the Noachian epoch, about 4.1 to 3.7 billion years ago. However, exactly where that water came from has long been a mystery. Some researchers argue that ancient Mars was always cold and dry, with sprawling ice caps that sometimes melted. During that period, the young Sun was only about 75% as bright as it is today, making sustained warmth difficult.
In their new research, Steckel and her colleagues set out to test whether Mars’ ancient climate was warm and wet or cold and dry. They used computer simulations to model how water might have shaped Mars’ landscape. Their findings suggest that rainfall or snowfall likely formed many of the valleys and headwaters still visible today. “It’s very hard to make any kind of conclusive statement,” Steckel said. “But we see these valleys beginning at a large range of elevations. It’s hard to explain that with just ice.”
Traces of water still visible today
Even now, satellite images show clear signs that water once flowed across Mars. Around the equator, vast networks of channels branch out from Martian highlands, much like tree roots, emptying into lakes—and possibly even an ocean. NASA’s Perseverance rover, which landed in 2021, is exploring Jezero Crater, the site of an ancient lake. During the Noachian, a powerful river flowed into this crater, leaving behind a large delta. “You’d need meters deep of flowing water to deposit those kinds of boulders,” said Brian Hynek, senior author of the study and a scientist at CU Boulder’s Laboratory for Atmospheric and Space Physics (LASP).
Building a digital Mars
To better understand Mars’ ancient climate, Steckel and Hynek created a digital model of part of the planet. The team used a computer simulation originally developed for Earth studies by study co-author Gregory Tucker, a professor in CU Boulder’s Department of Geological Sciences. Matthew Rossi, a research scientist at CU Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES), also contributed to the study. The researchers used the software to simulate how Mars’ landscape might have evolved over tens to hundreds of thousands of years. In some scenarios, they added precipitation, while in others they modeled melting ice caps.
They found striking differences: when ice caps melted, valleys formed mainly at high elevations. But with widespread precipitation, valleys and river headwaters appeared across a much broader range of elevations—from below Mars’ average surface to more than 11,000 feet high. “Water from these ice caps starts to form valleys only around a narrow band of elevations,” Steckel explained. “Whereas if you have distributed precipitation, you can have valley heads forming everywhere.”
A better match to the real Mars
The team compared their simulations to real data from NASA’s Mars Global Surveyor and Mars Odyssey spacecrafts. The scenarios that included rain or snow matched Mars’ actual landscape more closely than those relying on melting ice caps alone. While the researchers emphasize that their findings are not the final answer to Mars’ climate history, they offer valuable new insights. How ancient Mars stayed warm enough to allow snow or rain remains an open question. Still, Hynek sees the work as a major step forward. “Once the erosion from flowing water stopped, Mars almost got frozen in time and probably still looks a lot like Earth did 3.5 billion years ago,” he said.
Source: University of Colorado Boulder.
Image credit: NASA/JPLCaltech.
