Over the past 13 years, the four-wheeled Curiosity rover has traveled approximately 21 miles (34 kilometers) across the Martian surface to gather clues about the possibility of ancient life on the Red Planet. A recent discovery by the metallic explorer could provide an answer to the longstanding question of what happened to Mars’ atmosphere billions of years ago, and how the planet may have transformed from a wet, life-friendly world to a dry and arid desert.
The Curiosity rover recently uncovered large deposits of carbon within sulfate-rich layers of Mount Sharp in Mars’ impact basin, Gale Crater. In a paper published this month in the journal Science, data from three of Curiosity’s drill sites revealed an abundance of siderite—an iron carbonate mineral that had been a missing piece in the puzzle of Mars’ wet, habitable past.
Water and carbon dioxide react to form carbonate minerals. Based on the theory of Mars’ potentially habitable past, the planet may have once had a thick, carbon dioxide-rich atmosphere and liquid water on its surface. So if both water and carbon dioxide were present during Mars’ ancient past, then so should evidence of carbonate minerals. Previous discoveries, however, weren’t able to find sufficient amounts of carbonate to match the theory. That is until Curiosity’s recent discovery.
“The discovery of abundant siderite in Gale Crater represents both a surprising and important breakthrough in our understanding of the geologic and atmospheric evolution of Mars,” Benjamin Tutolo, associate professor at the University of Calgary, Canada, and lead author of the paper, said in a statement.
Although scientists have long suspected that Mars had an atmosphere rich in carbon dioxide, Curiosity’s findings are the first mineral evidence to support that theory. “It tells us that the planet was habitable and that the models for habitability are correct,” Tutolo added.
As Mars’ atmosphere thinned over time, the carbon dioxide transformed into rock form. The carbon dioxide had been warming the planet up until that time, and when it began to precipitate as siderite, it affected the planet’s ability to remain warm and maintain its surface water, according to the researchers.
Curiosity rover uses a drill attached to its arm to bore holes in Martian rock and collect the powdered samples from the rock into its belly. The rover drills about three to four centimeters into Mars’ subsurface, and the samples are deposited into its CheMin instrument, which uses X-ray diffraction to analyze rocks and soil. “Drilling through the layered Martian surface is like going through a history book,” Thomas Bristow, research scientist at NASA’s Ames Research Center, and coauthor of the paper, said in a statement. “Just a few centimeters down gives us a good idea of the minerals that formed at or close to the surface around 3.5 billion years ago.”
Since the carbonate minerals were found beneath the surface of Mars, the discovery suggests that they may be masked by other minerals in near-infrared satellite images of the planet from orbit. That may explain why previous missions have failed at finding evidence of carbonate minerals on Mars. If carbonate minerals are abundant in other sulfate-rich areas on Mars, that is enough to create conditions for a warm world with liquid water on its surface, according to the paper.
“Earth’s surface has been continuously habitable since about 3.5 billion years ago, but Mars’s surface evolved from more habitable early on, to uninhabitable today,” Edwin Kite, associate professor of geophysical sciences at the University of Chicago and third author on the paper, said in a statement. “This discovery helps us understand the mechanisms that drove the two planets down very different paths.”
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