NASA’s Curiosity rover has traveled 34 kilometers of the Martian surface over 13 years of exploration, collecting data on the Red Planet’s past. A recent analysis of samples from Gale Crater brought a groundbreaking discovery: large deposits of siderite, a mineral that could explain how Mars lost its atmosphere and went from a humid world to a barren desert.
In a paper published in the journal Science, scientists reported the discovery of siderite (iron carbonate) in the sulfate-rich layers of Mount Sharp. This mineral is the missing link in the theory that billions of years ago Mars had a thick atmosphere with carbon dioxide (CO₂) and liquid water. Previously, few carbonates have been found, but new data from three drilling locations confirm: CO₂ once warmed the planet, trapping heat, and then settled into rocks.
“The first direct evidence that Mars had a powerful carbon dioxide atmosphere. Now we understand how it disappeared and why the planet lost water,” notes Benjamin Tutolo of the University of Calgary, leader of the study.
How carbon dioxide turned Mars into a desert
According to the model, CO₂ and water interacted to form carbonate minerals. Subsequently, the atmosphere “settled” into the rocks, depriving the planet of its thermal blanket. Without CO₂, Mars would cool, and the water would freeze or evaporate, leaving only dry streambeds and salt lakes, traces of which are still being studied by scientists.
“When CO₂ settled into siderites, Mars lost its ability to retain heat. It’s like a page from the geologic diary of a 3.5 billion year old planet,” explains NASA’s Thomas Bristow.
Curiosity retrieved the samples using a drill that penetrates 3-4 centimeters into the rock. The powdered material enters the CheMin instrument where X-ray diffraction determines its composition. This technique also explained why carbonates were undetectable from orbit: they are hidden under layers of sulfates, which absorb infrared radiation. If similar deposits are common on Mars, it would confirm that it was once similar to early Earth.
Why did Earth and Mars take different courses?
“3.5 billion years ago, Earth was already supporting life and Mars was beginning to turn into a desert,” notes Edwin Kite of the University of Chicago. “Our discovery helps us understand why the two planets evolved so differently.”
The next step will be to search for carbonates in other regions of Mars to help reconstruct climate changes and assess the chances of ancient life. For now, Curiosity continues its journey, revealing new secrets of the Red Planet.
We previously reported on how Mars’ atmosphere was trapped inside rocks.
According to NASA
