Many pieces of evidence suggest that Mars once had a comfortable climate and abundant water, beneath a shroud of carbon dioxide-rich atmosphere. The carbon that once warmed the planet’s atmosphere has now been locked up in the Red Planet’s rusty rocks. Mars barely has any atmosphere left and is now a dry and cold desert.
Curiosity has unearthed carbon-rich minerals along its route up a Martian mountain. The finding is the first recorded instance of a carbon cycle on Mars. However, further studies have also revealed that the once life-friendly environment of Mars lost its ability to sustain life because the carbon cycle was too slow.
All that carbon dioxide must have gone somewhere, says geochemist Benjamin Tutolo of the University of Calgary in Canada, who also points to carbonate minerals, where carbon and oxygen might have gotten trapped. The dilemma in providing a concrete conclusion stems from the lack of carbonate found on the planet, which can explain the drying up of Mars.
Now, the Curiosity rover has revealed the presence of carbonate in the Gale Crater in the form of siderite, a carbonate of iron. Reaching this spot has been one of the goals of the Curiosity rover since it landed on Mars in 2012.
The rover drilled four samples from different rocks along an 89-meter stretch of terrain in the Gale crater. Researchers then analyzed the contents of the rocks with Curiosity’s onboard chemistry lab. The research team identified the presence of siderite in the sulfate-bearing layers. Events that led to the drying up of Mars, such as evaporation and water-rock interaction, may be the reason why this mineral is present on Mars.
The samples contained 5 to 10 percent siderite by weight, which, according to Tutolo, is sufficient to bring us closer to understanding what happened to all the CO₂ on the planet.
The rocks also contained iron oxyhydroxides, which were formed when siderite dissolved in acidic water. This led to the release of carbon dioxide back into the atmosphere, suggesting the presence of a carbon cycle. However, unlike Earth, where a stable carbon cycle has been continuing for billions of years, Mars’ rocks absorbed more carbon dioxide than what was released. CO₂ levels decreased, but never returned to their original levels, and that is key to understanding how the habitable Martian environment became inhabitable.
The presence of siderite suggests the existence of a thick, carbon dioxide-laden atmosphere, which was eventually lost. The atmosphere was also sufficiently able to allow the presence of liquid water on the surface of the Red Planet. The best way to study the samples further is to bring them back to Earth. Finding a correlation between carbonate-rich rocks and other types of rock samples can also provide valuable information about the missing carbon on Mars.
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