Mars is one of our closest planetary neighbors and has fascinated people for hundreds of years, partly because it is so similar to Earth. It is of the same size, contains similar rocks and minerals, and is not far from the sun.

Because Mars and Earth have many characteristics, scientists have long wondered if Mars could have had a life. Today, Mars is very cold and dry, with no liquid water on the surface, making it a hostile environment for life. But some observations suggest that ancient Mars might be warmer, wetter and more beneficial to life.

Even though scientists observed the surface of Mars to the conclusion that it used to be warmer than it is today, they have not found much concrete evidence to prove what causes it to warm. But a study published by my colleagues and I in April 2025 showed that carbonate minerals exist on Earth, which could help solve the problem.

Carbonate minerals contain carbon dioxide, which heats planets when present in the atmosphere. These minerals suggest that carbon dioxide could have previously existed in larger quantities in the atmosphere and provide exciting new clues to the ancient Mars environment.

As a geochemicalist and astrobiologist who has been studying Mars for over 15 years, I am fascinated by the past and the idea that Mars was past and possibly habitable.

Ancient carbon cycles on Mars in the past

Mars observations of orbiting satellites and wanderers show that rivers and dry lakes have shown that there was once liquid water on the surface of Mars. These instruments found minerals on the surface, and scientists could analyze them to understand what Mars used to look like.

If Mars had liquid water in ancient times, it would require a much warmer climate than today. Warm planets usually have a strong atmosphere that captures heat. So maybe the Martian atmosphere used to be thicker and consists of heat absorption of carbon dioxide. If Mars did have a thicker atmosphere of carbon dioxide, scientists predict that they would be able to see traces of this atmospheric carbon dioxide on the surface of Mars today.

Gasy carbon dioxide dissolves in water, a chemical process that can ultimately help form solid minerals on and below the planet's surface - essentially removing carbon dioxide from the atmosphere. Many scientists have previously tried to find carbonate minerals on the surface of Mars, and one of the excitement about the warmer, wetter early Mars in Mars was that it might be an environment suitable for ancient microbial life.

Find carbonate on Mars

Previous searches for carbonate on Mars have been observed in meteorites and in two craters on Mars: Gusev Crater and Jezero Crater. However, there is not enough time to explain the warm climate on Mars in the past.

Over the past few years, curious rovers at the Mars Science Laboratory have been traversing an area called Gale Crater. Here, the chemical and mineralogical instruments of the mobile station discovered many iron-rich carbonate mineral iron ore.

As my colleagues and I detailed in new research on these results, this carbonate mineral may contain some of the missing atmospheric carbon dioxide needed for warmer, wetter early Mars.

The mobile station also found iron hydroxyoxygen oxide minerals, which showed that the rocks later dissolved when they encountered water, releasing a portion of the carbon dioxide back into the atmosphere. Despite its very thinness, the modern Martian atmosphere is still composed mainly of carbon dioxide.

In other words, these new results provide evidence for the ancient carbon cycle on Mars. The carbon cycle is the process of transferring carbon dioxide between different reservoirs, such as rocks on the surface and gases in the atmosphere.

Potential habitat for past microbial life spans on Mars

Scientists generally believe that if liquid water is contained, it is considered inhabitable. Nutrients such as carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur and necessary trace elements; energy; and less harsh conditions - not too acidic, too salty or too hot.

As observations from the Great Wind Crater and other locations on Mars suggest that Mars may have habitable conditions, can Mars host life? If so, how will the researchers tell?

Although microorganisms are too small to detect human eyes, they can remain evidence of preservation in rocks, sediments and soil. Organic molecules in these microorganisms are sometimes preserved in rocks and sediments. And certain microorganisms can form minerals or have cells that form certain shapes. This past evidence is called biosignature.

Collect Mars samples

If Mars has biosignatures on or near the surface, researchers want to know they have the right tools to detect them.

So far, wanderers on Mars have discovered that some organic molecules and chemical characteristics may come from non-biological - non-life - sources or past lives.

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However, it is not easy to determine whether the planet used to host life. Analysis conducted in the Earth Laboratory can provide clearer clarity in the origin of these signatures.

To this end, Mars Perseverance Rovers have been collecting and sealing samples on Mars in 2020, with one cache on the surface of Mars and the other on the rover.

These caches include samples of rock, soil and atmosphere. Their content can tell researchers about many aspects of Mars' history, including past volcanic activity, meteorite impacts, streams and lakes, wind and sandstorms, and past Martian life. If these samples are brought to Earth, scientists can check here for them to have signs of ancient life on another planet.