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The findings from NASA’s Curiosity rover have uncovered an important aspect of Mars’ geological history, revealing that carbon once responsible for warming the planet’s atmosphere has been trapped in its rocks for millions of years. This discovery could reshape our understanding of Mars’ past climate and the potential for life on the planet.
The recent study, published in Science, highlights the first substantial evidence of a carbon cycle on Mars. Researchers suggest that the slow nature of this carbon cycle may explain why the once-hospitable climate of Mars eventually transitioned to the cold and arid environment seen today.
For decades, the scientific community has recognized that Mars was once a world rich in water and maintained a warmer climate, sustained by a dense carbon dioxide atmosphere. However, current observations show that the Martian landscape has largely become a desolate desert with an extremely thin atmosphere. Geochemist Benjamin Tutolo from the University of Calgary emphasizes, "All that carbon dioxide must have gone somewhere," speculating that it has been sequestered within carbonate minerals.
Despite extensive observations over the years, scientists were puzzled by the apparent scarcity of carbonate minerals that could account for such a significant loss of atmospheric carbon. "One of the biggest questions in the history of Mars is, where is all the carbonate?" remarked Tutolo. With Curiosity’s recent findings, this question may be moving towards resolution.
During its exploration of Gale crater’s ancient lakebed, Curiosity identified a particular carbonate mineral known as siderite. This marks the first discovery of this mineral in that region. Tutolo expressed excitement over this finding, as it holds the potential to unlock further insights into Mars’ past.
The rover’s journey covered a key area where rock types transition from muddy clays to sulfate-rich minerals, a major research objective since the rover’s arrival in 2012. The analysis involved drilling samples from various rocks across an 89-meter stretch and utilizing the rover’s onboard laboratory for chemical analysis.
The presence of siderite in these sulfate-bearing layers suggests it formed during Mars’ drying process, likely due to a combination of evaporation and water-rock interactions. Tutolo pointed out the unexpected abundance of siderite, comprising between 5 and 10 percent of the weight in the samples examined. This finding holds significant implications: if similar quantities of siderite are present in other Martian minerals, it could enhance our understanding of the fate of CO2 that once filled the atmospheres.
Additionally, the samples contained varying levels of iron oxyhydroxides. Their formation hints that some carbon may have cycled back to the atmosphere, albeit in a much less balanced manner than on Earth. Tutolo stresses that, contrary to Earth’s relatively stable carbon cycle, Mars has absorbed considerably more carbon than it has released over geological time. "CO2 goes down, it doesn’t come back up," he explained, emphasizing how this understanding could clarify why Mars transformed from a potentially habitable world to one that is now inhospitable.
Planetary scientist Janice Bishop from the SETI Institute acknowledged that these insights help clarify the fate of the carbonate and how Mars could have once supported liquid water. She advocates for a detailed examination of orbital data to identify further connections between carbonates and different rock types. However, she also emphasizes that examining Martian samples back on Earth would provide the most comprehensive understanding of their composition and history.
As researchers continue to uncover tantalizing evidence regarding Mars’ carbon cycle, these findings may help unravel the mysteries of the Red Planet’s past and contribute to the broader narrative of planetary habitability.
Source
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