Mars, one of our closest planetary neighbors, has fascinated people for hundreds of years, partly because it is so similar to Earth. It is about the same size, contains similar rocks and minerals, and is not too much farther out from the Sun.
Because Mars and Earth share so many features, scientists have long wondered whether Mars could have once harbored life. Today, Mars is very cold and dry, with little atmosphere and no liquid water on the surface − traits that make it a hostile environment for life. But some observations suggest that ancient Mars may have been warmer, wetter and more favorable for life.
Even though scientists observing the surface of Mars conclude that it was once warmer than it is today, they haven’t been able to find much concrete evidence for what caused it to be warmer. But a study my colleagues and I published in April 2025 indicates the presence of carbonate minerals on the planet, which could help solve this puzzle.
Carbonate minerals contain carbon dioxide, which, when present in the atmosphere, warms a planet. These minerals suggest that carbon dioxide could have previously existed in the atmosphere in larger quantities and provide exciting new clues about ancient Mars’ environment.
As a geochemist and astrobiologist who has studied Mars for more than 15 years, I am fascinated by Mars’ past and the idea that it could have been habitable.
Ancient carbon cycle on past Mars
Observations of Mars from orbiting satellites and rovers show river channels and dry lakes that suggest the Martian surface once had liquid water. And these instruments have spotted minerals on its surface that scientists can analyze to get an idea of what Mars may have been like in the past.
Today, Mars is very cold, with a thin atmosphere and dry climate. But in the ancient past, it may have been warmer and wetter, with a thicker heat-trapping atmosphere.
NASA/J. Bell – Cornell U./M. Wolff – SSI via AP, File
If ancient Mars had liquid water, it would have needed a much warmer climate than it has today. Warmer planets usually have thick atmospheres that trap heat. So, perhaps the Martian atmosphere used to be thicker and composed of heat-trapping carbon dioxide. If Mars did once have a thicker carbon dioxide-containing atmosphere, scientists predict that they’d be able to see traces of that atmospheric carbon dioxide on the surface of Mars today.
Gaseous carbon dioxide dissolves in water, a chemical process that can ultimately contribute to formation of solid minerals at and below the surface of a planet − essentially removing the carbon dioxide from the atmosphere. Lots of scientists have previously tried to find carbonate minerals on the surface of Mars, and part of the excitement about a warmer, wetter early Mars is that it could have been a suitable environment for ancient microbial life.
Finding carbonates on Mars
Previous searches for carbonates on Mars have turned…
