NASA's Curiosity rover has made an important discovery that sheds light on the climate history of the Red Planet. For the first time, direct evidence of the carbon cycle, which was previously only theorized, has been found on Mars. During excavations in Gale Crater, Curiosity discovered siderite, a mineral that could only form through the precipitation of carbon in the atmosphere.
This discovery shows that Mars had an active carbon cycle about 3.5 billion years ago, supporting predictions about the planet's habitability. Geochemist Prof. Dr. Benjamin Tutolo from the University of Calgary stated, "This finding tells us that Mars was habitable, and our models about this are accurate."
For years, the scientific community has been searching for evidence of water on Mars. Surface features such as lakes, rivers, and ocean remnants suggest that liquid water once existed in abundance. However, for water to exist, there must have been sufficient carbon dioxide in the atmosphere.
Tutolo explained, "Models predicted that carbonate minerals should be widespread on the Martian surface, but until now, neither orbiting satellites nor surface vehicles have found clear evidence of these minerals."
Through X-ray diffraction analyses conducted by Curiosity in 2022 and 2023, siderite was found in almost pure crystal form in samples collected from different points of the crater. This mineral contains iron, carbon dioxide, and trace amounts of magnesium.
Siderite had not been previously detected on the Martian surface. The reason for this was that water-soluble magnesium sulfate salts, which were observed from orbit, had suppressed the signal of carbonate minerals. The research team concluded that these minerals are likely widespread across Mars and may be hidden in these regions.
This discovery not only confirms models suggesting that ancient Mars had a warmer and more habitable atmosphere, but it also provides new clues about why the planet was unable to sustain these conditions. Tutolo added, "The ancient Mars carbon cycle appears to have been unstable. That is, much more carbon dioxide was trapped in rocks than was released into the atmosphere, which may have threatened the long-term habitability of the planet."
The team now has a better understanding of why minerals like siderite were not detected by orbital vehicles, which will enable the re-analysis of past data. Additionally, more carbonate minerals may be found in samples collected by exploration vehicles like Curiosity.
This discovery not only sheds light on Mars' past but also offers a new perspective for carbon capture technologies used in combating climate change on Earth. Prof. Dr. Tutolo remarked, "I have been working on carbon capture on Earth for years. Now, studying these minerals on Mars and applying this knowledge to understand the past of another planet has been an experience I could never have imagined."
The findings were published in the journal Science Advances.
