A mineral known as siderite has been discovered in rock samples drilled by NASA’s Curiosity rover on Mars, providing new insights into the planet’s ancient, warmer, and wetter conditions. This finding supports the theory that Mars once had significant bodies of water and possibly even life.
Since landing on Mars in 2012, the Curiosity rover has been examining whether our neighboring planet could have supported microbial life. The mineral was detected in samples taken from three different locations within Gale Crater, a large impact site featuring a central mountain, during the years 2022 and 2023.
Siderite is an iron carbonate mineral, and its presence in sedimentary rocks dating back billions of years indicates that Mars once had a dense atmosphere rich in carbon dioxide. This atmospheric condition could have created a greenhouse effect, warming the planet enough to sustain liquid water on its surface.
Many researchers believe that certain features on the Martian landscape suggest the past existence of liquid water, with potential oceans, lakes, and rivers that could have served as habitats for early microbial life.
On Earth, as well as on Mars and Venus, carbon dioxide is a crucial greenhouse gas that regulates climate by trapping heat from the sun.
Previously, evidence confirming a carbon dioxide-rich atmosphere on Mars had been quite limited.
The prevailing theory suggests that the Martian atmosphere underwent a transformation from a thick, carbon dioxide-rich environment to a thin, depleted one. This shift, reasons for which remain unclear, led to carbon becoming trapped in the planet’s crust as carbonate minerals.
The Curiosity rover drills into rock to examine its chemical and mineral composition, and the samples it collected showed a siderite content of up to 10.5% by weight, measured by an onboard instrument.
“A major question in the field of Martian planetary evolution and its potential for habitability is: if significant amounts of carbon dioxide were necessary to warm the planet and support liquid water, why have we detected so few carbonate minerals on Martian surfaces?” said Benjamin Tutolo, a geochemist from the University of Calgary, who is part of the NASA Mars Science Laboratory Curiosity rover team and the lead author of a study published in the journal Science.
“Models indicate that carbonate minerals should be plentiful. Yet so far, both rover-based examinations and satellite surveys have shown minimal evidence of this,” Tutolo added.
Given that rock types similar to those sampled by the rover have been found across Mars, researchers believe they may also contain a wealth of carbonate minerals, potentially storing a significant amount of the carbon dioxide that once warmed the planet.
The sedimentary rocks in Gale Crater, including sandstones and mudstones, are believed to have been deposited around 3.5 billion years ago, during a time when the area was a lake before the climate of Mars drastically shifted.
“The transition of Mars from a more habitable environment in its past to the seemingly lifeless one we see today represents the largest-known ecological disaster,” remarked planetary scientist Edwin Kite from the University of Chicago and Astera Institute, who co-authored the study.
“The cause of this transformation remains unknown, but today, Mars has a very thin atmosphere composed mostly of carbon dioxide, with evidence suggesting it was once much thicker. Understanding what happened to that carbon is essential, making the discovery of this unexpected deposit of carbon-rich materials an important clue,” Kite noted.
The findings from the rover provide valuable information regarding the carbon cycle on ancient Mars.
On Earth, volcanoes release carbon dioxide into the atmosphere, which is then absorbed by bodies of water like oceans and reacts with calcium to form limestone. This rock eventually re-enters the atmosphere through volcanic activity due to geological processes such as plate tectonics. However, Mars does not have plate tectonics.
“One significant feature of the ancient carbon cycle on Mars highlighted in our study is that it appears to have been out of balance. In other words, it seems that a much larger amount of carbon dioxide was locked away in rocks than was eventually released back into the atmosphere,” Tutolo explained.
“Our new analyses can now be integrated into models of Martian climate evolution, helping to refine our understanding of the role of this unbalanced carbon cycle in both sustaining and ultimately losing the planet’s habitability throughout its history,” Tutolo added.
