Curiosity rover finds ripples proving Mars once had ice-free lakes

Billions of years ago, Mars was not the frozen desert we see today. Water moved across its surface, pooled in basins, and shaped the landscape under an atmosphere thick enough to carry wind. NASA's Curiosity rover has now found the clearest evidence yet of what that world looked like: two sets of wave ripples, preserved in stone, that could only have formed in open water, unencumbered by ice.

In November 2022, Curiosity photographed a thin, dark layer of rock called the Amapari Marker Band in the foothills of Mount Sharp, which rises from the floor of Gale Crater. Within that band, scientists recognized the unmistakable signature of ancient waves—ripples that had once moved across a sandy shoreline. Weeks later, the rover imaged a second set of ripples in a nearby rock formation called the Prow outcrop, this one marking what had been the lake bed itself. Both discoveries point to the same conclusion: liquid water, exposed to the Martian atmosphere, shaped by wind, existed here roughly 3.7 billion years ago.

The significance lies not just in the presence of water, but in its form. Earlier rovers, including Opportunity beginning in 2004, had found evidence of water flowing across Mars' ancient surface. But flowing water and pooled water tell different stories about a planet's climate. Flowing water could have come from melting ice or underground sources. Pooled water—a lake—suggests something warmer, something more stable, something closer to habitable. The ripples themselves are the key. As Caire Mondro, a postdoctoral researcher at the California Institute of Technology, explained, the specific shape of these ripples could only form under water that was open to the air and disturbed by wind. If the water had been covered in ice, the ripples would look different. They would not exist at all.

Using computer modeling, Michael Lamb, a geology professor at Caltech, analyzed the size and spacing of the ripples to estimate the lake's depth. The numbers were modest: less than six feet, or roughly two meters. A shallow body of water, but a body of water nonetheless—the kind of place where, under the right conditions, microbial life might have emerged and persisted.

This discovery arrives a decade after Curiosity first found evidence of long-lived ancient lakes on Mars in 2014. That earlier work established that water had pooled on the planet's surface for extended periods. The new ripples refine that picture considerably. They show that at least some of those lakes were free of ice, suggesting Mars' early climate was warmer and more clement than many scientists had theorized. The planet was drying up when these ripples formed, yet it was still wet enough, still warm enough, to support open bodies of water shaped by wind.

The implications ripple outward. If Mars maintained such conditions—liquid water, an open atmosphere, relative warmth—even as it transitioned toward the cold, dry world we know today, the window for life to have emerged was perhaps wider and more favorable than previously understood. The research was published in the journal Science Advances in mid-January, and it stands as a reminder that the story of Mars is not one of a planet that was always dead. For a time, it was alive with water.