Curiosity Finds Evidence of Open Water on Ancient Mars

NASA’s Curiosity Rover has been exploring Mars since 2012 and has recently discovered evidence of ancient ponds and lakes that were ice-free on the planet’s surface. The rover identified small undulations resembling those found in sandy lakebeds on Earth.

These features are believed to have formed as wind-driven water moved back and forth across the surface. The conclusion is that the water was exposed to the elements rather than covered by ice. Researchers suggest these ripples date back approximately 3.7 billion years.

Mars, the fourth planet in our Solar System and the second smallest of the major planets, is distinguished by its striking red color caused by iron oxide in its surface material.

Curiosity Finds Evidence of Open Water on Ancient Mars
Images taken by the Curiosity rover of wave ripples on Mars, annotated by the researchers. (Mondro et al., Science Advances, 2025)

Classified as a terrestrial planet, Mars shares some similarities with Earth, such as valleys, volcanoes, and evidence of ancient riverbeds. However, the similarities end there. Mars has polar caps primarily made of carbon dioxide ice, an unbreathable atmosphere, and a surface that is both cold and dry.

Mars has long captivated human curiosity, initially due to vague suggestions of alien intelligence and, more recently, because of the possibility that it may have once been habitable.

Curiosity Finds Evidence of Open Water on Ancient Mars
A full-disk view of Mars, courtesy of VMC. (ESA)

One rover exploring Mars is NASA’s Curiosity Rover, launched in 2011 and landing on Mars in August 2012. It has since been exploring the area around Gale Crater.

The rover’s primary mission is to study the planet’s climate and geology to determine if it could have once supported primitive life. To achieve this, Curiosity is equipped with a wide range of tools, including drills for soil sampling and instruments to analyze atmospheric conditions.

In a recent paper published in Science Advances, Caltech researchers John Grotzinger, Harold Brown Professor of Geology, and Michael Lamb, Professor of Geology, shared their findings.

Curiosity Finds Evidence of Open Water on Ancient Mars
New simulations are helping inform the Curiosity rover’s ongoing sampling campaign. (NASA/JPL-Caltech/MSSS)

The researchers discovered two sets of what appear to be ancient wave ripples on the Martian surface. These ripples, preserved in rock, are thought to have formed in dried-up bodies of water.

The ripples are small undulations, similar to those observed on Earth’s beaches and lakebeds, where wind-driven water shapes the shallows. The discovery is significant because it suggests the water was liquid and open to the atmosphere, not frozen.

The ripples identified in Gale Crater are some of the most compelling evidence yet that Mars once hosted bodies of liquid water. Based on the analysis, these ripples likely formed around 3.7 billion years ago.

This finding implies that Mars’s atmosphere and climate were once much warmer and denser, sufficient to support liquid water under open air.

Using computer models of the ripples, the team estimated the size of the lake. The ripple height of 6 mm and separation of 4 to 5 cm indicate that the lake was relatively shallow, possibly less than 2 meters deep.

Curiosity Finds Evidence of Open Water on Ancient Mars
NASA’s Curiosity rover continues to search for signs that Mars’ Gale Crater conditions could support microbial life. (NASA/JPL-Caltech/MSSS)

One set of ripples, known as the Prow outcrop, was found in an area that was once a wind-blown dune field. The other set was discovered nearby in the sulfate-rich Amapari Marker Band of rocks.

The two regions represent slightly different periods, suggesting that the warm, dense atmosphere occurred multiple times or persisted for an extended duration.

This discovery provides valuable insights into Mars’s paleoclimate, helping scientists map the planet’s changing conditions.

Although NASA’s Opportunity Rover was the first mission to identify ripples on the Martian surface, the nature of the water bodies remained uncertain.

The latest findings offer a deeper understanding of early Mars, hinting that liquid water may have been scattered across the landscape. Further exploration is needed to determine how widespread these ripples are.



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