Recently, the NASA rover discovered a significant amount of siderite, a carbon-rich mineral, while drilling on Mars. This finding provides new evidence for the presence of abundant water bodies, a dense atmosphere, and an inhabitable environment on Mars in ancient times.
According to a report by Reuters, the discovery was made by NASA’s Curiosity rover, which landed on Mars in 2012. Between 2022 and 2023, the Curiosity rover extracted rock samples from three locations in the Gale Crater on Mars, revealing the presence of this mineral.
Siderite is a carbonate mineral with a chemical composition of iron carbonate (FeCO₃). This mineral was formed in sedimentary rocks billions of years ago, suggesting that Mars might have had a thick, carbon dioxide-rich atmosphere at that time. Such climate conditions could have used the greenhouse effect to heat the planet, supporting the presence of liquid water on the surface.
Scientists have long speculated that many surface features on Mars are related to past water activities, including the presence of oceans, lakes, and rivers, which could have been potential habitats for early microbial life.
Similar to Earth and Venus, carbon dioxide is the primary greenhouse gas in Mars’ atmosphere, effectively trapping solar heat and raising surface temperatures.
However, direct evidence confirming Mars’ early high concentrations of carbon dioxide has been scarce. According to the mainstream hypothesis, Mars may have had a dense atmosphere in its early history, but for unknown reasons, it gradually evolved into the thin atmosphere seen today. This lost carbon may have been sequestered in the crust as carbonate minerals.
Based on the latest analysis by the Curiosity rover, the samples showed a high content of siderite, reaching up to 10.5% by weight, indicating a much higher level of carbon sequestration than expected. The rover is equipped with instruments that can drill into Mars rocks 3 to 4 cm deep and directly analyze the minerals and chemical composition.
Benjamin Tutolo, a geochemist at the University of Calgary in Canada and a member of NASA’s Mars Science Laboratory team involved in this research, noted that the Curiosity rover’s new discovery resolves a long-standing question that has perplexed researchers.
“The core question of whether Mars was once habitable has always been perplexing – if there was indeed a significant amount of carbon dioxide initially to stabilize the climate and liquid water, why do we find almost no traces of carbonate minerals?” Tutolo said. While models predict widespread distribution of carbonate minerals on Mars’ surface, evidence from orbital observations and ground exploration has been extremely limited.
The research team indicated that rocks similar to the samples are widely distributed on Mars, suggesting that carbonate minerals may be common in the Martian crust, harboring significant amounts of sequestered carbon dioxide.
The sedimentary rocks in the Gale Crater, including sandstone and mudstone, are estimated to have formed about 3.5 billion years ago when the region may have been a lake, yet to experience dramatic Martian climate changes.
Edwin Kite, a planetary scientist at the University of Chicago and the Astera Research Institute, and a co-author of the study, stated, “The transition of Mars from a potentially habitable, warm, and wet surface early on to the dry, cold, and barren appearance today is one of the most significant planetary climate catastrophes we know.”
“We have yet to determine the cause of this transition, but there are indications that Mars had a denser atmosphere in its early days. This makes us even more eager to learn where that carbon ultimately went. Discovering such high-carbon mineral layers, not previously anticipated, is a critical breakthrough in unraveling the mystery of Martian climate evolution.”
This discovery also contributes to understanding carbon cycling patterns on ancient Mars.
On Earth, volcanoes release carbon dioxide into the atmosphere, which is then absorbed by oceans and combined with elements like calcium to form carbonate rocks (such as limestone). With the movement of tectonic plates, these rocks are heated, releasing carbon back into the atmosphere.
Mars, however, lacks tectonic activity. Tutolo explained, “The carbon cycle of ancient Mars was out of balance, meaning there was far more carbon dioxide sequestered in rocks than being later released into the atmosphere.”
He added, “This study can be incorporated into models of Mars’ climate evolution, helping us better understand why Mars lost its early potential habitability and the role carbon cycling played in it.”