NASA’s Curiosity rover found siderite, an iron carbonate mineral, within the rocky layers of Mount Sharp in Mars’ Gale Crater. This discovery could provide an answer to the mystery of what happened to the planet’s geologic and atmospheric evolution.
Researchers have long believed that Mars once had a thick, carbon dioxide-rich atmosphere and liquid water on the planet’s surface. That carbon dioxide and water should have reacted with Martian rocks to create carbonate minerals. Until now, though, rover missions and near-infrared spectroscopy analysis from Mars-orbiting satellites haven’t found the amounts of carbonate on the planet’s surface predicted by this theory. That is, until the discovery of siderite, as reported in an April Science paper led by the University of Calgary’s Benjamin Tutolo.
The discovery of this carbonate mineral in rocks beneath the surface suggests that carbonate may be masked by other minerals in near-infrared satellite analysis.
“The thin atmosphere of Mars is predominantly carbon dioxide, and models of Mars have long speculated that carbonate minerals should be common on Mars if the atmosphere was thicker in the past,” said David Vaniman, a senior scientist at the Planetary Science Institute and coauthor on the paper. “This is generally assumed to be the case as there’s evidence of past liquid water on the surface. Hints of carbonate minerals have been provided by landers and from orbit, but not in the abundances and widespread distribution expected.”
Other PSI co-authors include Nicholas Castle, Patricia Craig and Steve Chipera.
“Curiosity detected siderite traces early in its deployment, but has repeatedly detected slightly more in Gale Crater,” Vaniman said. “This was completely unexpected, since no carbonate had been detected from orbit at Gale crater.”
What’s more, the siderite found is pure iron carbonate mineral, meaning it doesn’t contain positively charged Calcium and Magnesium atoms, common among the carbonate minerals in Martian meteorites that formed directly in altered basalt.
“Rather, the siderite at Gale crater is different,” Vaniman said. “It appears to have formed from waters in which acidic reactions had been neutralized, so that the positively-charged Calcium and Magnesium were separated and formed later as sulfates. Comparable sulfate deposits are common on Mars. If they too contain carbonate minerals hidden from orbital detection, this may go a long way toward solving the ‘missing carbonate’ question on Mars.”
