Over the past 13 years, the four-wheeled Curiosity rover has traveled approximately 21 miles (34 kilometers) across the Martian surface, collecting clues to the possibility of ancient life on the Red Planet. The recent discovery of the metallic explorer may answer the long-standing question of what happened to Mars’ atmosphere billions of years ago, and how the planet could have transformed from a humid, life-friendly world into a dry and waterless desert.
Recently, the Curiosity rover discovered large deposits of carbon in the 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 Curiosity drilling sites revealed large amounts of siderite, an iron carbonate mineral that has been a missing piece in the puzzle of Mars’ wet, habitable past.
Water and carbon dioxide react to form carbonate minerals. According to 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 in Mars’ ancient past, then there should be evidence of carbonate minerals. However, previous discoveries failed to find enough carbonates to support this theory. Until Curiosity’s recent discovery.
“The discovery of large quantities of siderite in Gale Crater is both surprising and an important breakthrough in our understanding of the geological and atmospheric evolution of Mars,” said Benjamin Tutolo, an assistant professor at the University of Calgary, Canada, and lead author of the paper, 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 this theory. “This tells us that the planet was habitable and that the models of habitability are correct,” Tutolo added.
Over time, Mars’ atmosphere thinned out, and carbon dioxide turned to rock. Until now, carbon dioxide has been warming the planet, and when it began to settle as siderite, it affected the planet’s ability to stay warm and support surface water, according to researchers.
The Curiosity rover uses a drill attached to its arm to drill holes in the Martian rock and collect powdered samples from the rock in its belly. The rover goes down about three to four centimeters into the interior of Mars, and the samples are sent to the CheMin instrument, which uses X-ray diffraction to analyze rocks and soil. “Drilling through the layered Martian surface is like flipping through a history book,” said Thomas Bristow, a research scientist at NASA’s Ames Research Center and co-author of the paper, in a statement. “Just a few centimeters down gives us a good idea of the minerals that formed at or near the surface about 3.5 billion years ago.”
Because the carbonate minerals were found below the surface of Mars, the discovery suggests that they may be masked by other minerals in satellite images of the planet from near-infrared orbit. This may explain why previous missions have failed to find evidence of carbonate minerals on Mars. If carbonate minerals are common in other sulfate-rich areas of Mars, this is enough to create the conditions for a warm world with liquid water on the surface, the article says.
“The surface of the Earth was continuously habitable until about 3.5 billion years ago, but the surface of Mars has evolved from being more habitable in the beginning to being uninhabitable today,” said Edwin Kite, an associate professor of geophysical sciences at the University of Chicago and the third author of the paper. “This discovery helps us understand the mechanisms that led the two planets to take very different paths.”
