NASA’s Curiosity Rover has discovered that the Martian surface was once mild enough for liquid water. In 2022, it found ripples in rock in the Gale Crater that resemble the wave patterns on a sandy lake bed on Earth.
We already know that ice exists at the planet’s poles and that its thin atmosphere contains water vapor. We even know of ancient frozen lakes. Last year, NASA’s Insight lander discovered reservoirs of liquid water ten kilometers deep inside the Martian crust.
But never before have we seen that surface liquid water once existed on Mars.
“The shape of the ripples could only have been formed under water that was open to the atmosphere and acted upon by wind,” said Claire Mondro, lead author of the new study.
Around 3.7 million years ago, the climate on Mars was above freezing. The Rover discovered two sets of ripples, which are just six millimeters high and four to five centimeters apart. To learn more about the ancient lake, researchers combined the ripple measurements with computer modeling. It turns out that the lake was quite shallow, around two meters at its deepest point.
Images of the ripples found on Mars. Photo: Mondro et al., 2025
Did life exist, too?
This discovery contradicts the assumption that the planet was cold and arid during that era. It also means that Mars once had a much thicker atmosphere, capable of retaining heat. This means Mars also had more scope to harbor microbial life.
The ripples happened when the planet was becoming drier, and the two sets also formed at different times. This means that either the planet was warm enough to have liquid water for far longer than expected or that a denser atmosphere existed more than once in the planet’s history.
“Extending the length of time that liquid water was present extends the possibilities for microbial habitability later into Mars history,” Mondro said.
Understanding the planet’s climatic history and the role of liquid water is crucial for assessing Mars’s habitability and guiding the ongoing search for past life
