A discovery made by a NASA rover, detailed in a study published Wednesday, shows that Mars remained a desert, although rivers flowed intermittently. This explains why the Red Planet remained devoid of any life forms, unlike its closest counterpart, Earth.
Mars is believed to have had all the necessary ingredients for life, most notably water, as the surface of the planet closest to Earth is dotted with traces of ancient lakes and rivers.
Several robotic rovers sent to Mars are currently focused on searching for traces of life forms that may have existed on the Red Planet millions of years ago.
Earlier this year, the Curiosity rover discovered a missing piece in this fragmented picture: rocks rich in carbonate minerals. Similar to limestone on Earth, these rocks formed like sponges made from carbon dioxide captured from the atmosphere.
A new study published in the scientific journal Nature has developed a precise model of how these rocks contributed to changing scientists' understanding of Mars' past.
The study's lead author, Edwin Kite, a planetary scientist at the University of Chicago, explained to AFP that the planet likely experienced "brief phases when life was possible at specific times and places." But these "oases" were the exception, not the rule.
On Earth, atmospheric carbon dioxide warms the planet. Over long periods, it forms carbonaceous rocks. Volcanic eruptions then release the gas into the atmosphere, creating a climate cycle that maintains the water cycle.
However, according to Kite, Mars experienced a "lower" rate of carbon-rich volcanic gas release than Earth. This led to an imbalance that made the planet colder and less hospitable to life.
The researchers' modeling showed that the brief phases of liquid water on Mars were followed by a desert phase that lasted 100 million years, too long for any life to have survived.
However, the researcher does not rule out the possibility of pockets of liquid water buried deep beneath the surface.
Another NASA rover, Perseverance, which landed in 2021 in another ancient delta on the planet, also found traces of carbonate rocks on the edge of a dried-up lake.
However, to determine the truth requires analyzing samples of these rocks on Earth, as observed by American, European, and Chinese space programs.
Ultimately, scientists are seeking an answer to one of the biggest questions preoccupying humanity: Is Earth the only planet harboring life?
Astronomers have discovered approximately 6,000 exoplanets to date, but all of them are so distant that it seems impossible to retrieve samples from them.
Kate uses this point to emphasize the importance of bringing back samples from Mars, as it would reveal whether the planet even contained microorganisms during its watery period. If this hypothesis proves false, it would be an indicator of how difficult it is for life to exist on planets other than Earth.
If these samples confirm traces of previously existing life forms, this would, in Kate's opinion, constitute evidence that "life is easy to come by on a planetary scale."
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