A roughly 3.5-mile high Martian mound that scientists suspect preserves evidence of a massive lake might actually have formed as a result of the Red Planet’s famously dusty atmosphere, an analysis of the mound’s features suggests. If correct, the research could dilute expectations that the mound holds evidence of a large body of water, which would have important implications for understanding Mars’ past habitability.
Researchers based at Princeton University and the California Institute of Technology suggest that the mound, known as Mount Sharp, most likely emerged as strong winds carried dust and sand into the 96-mile-wide crater in which the mound sits. They report in the journal Geology that air likely rises out of the massive Gale Crater when the Martian surface warms during the day, then sweeps back down its steep walls at night. Though strong along the Gale Crater walls, these “slope winds” would have died down at the crater’s center where the fine dust in the air settled and accumulated to eventually form Mount Sharp, which is close in size to Alaska’s Mt. McKinley.
This dynamic counters the prevailing theory that Mount Sharp formed from layers of lakebed silt — and could mean that the mound contains less evidence of a past, Earth-like Martian climate than most scientists currently expect. Evidence that Gale Crater once contained a lake in part determined the landing site for the NASA Mars rover Curiosity. The rover touched down near Mount Sharp in August with the purpose of uncovering evidence of a habitable environment, and in December Curiosity found traces of clay, water molecules and organic compounds. Determining the origin of these elements and how they relate to Mount Sharp will be a focus for Curiosity in the coming months.
But the mound itself was likely never under water, though a body of water could have existed in the moat around the base of Mount Sharp, said study co-author Kevin Lewis, a Princeton associate research scholar in geosciences and a participating scientist on the Curiosity rover mission, Mars Science Laboratory. The quest to determine whether Mars could have at one time supported life might be better directed elsewhere, he said.
“Our work doesn’t preclude the existence of lakes in Gale Crater, but suggests that the bulk of the material in Mount Sharp was deposited largely by the wind,” said Lewis, who worked with first author Edwin Kite, a planetary science postdoctoral scholar at Caltech; Michael Lamb, an assistant professor of geology at Caltech; and Claire Newman and Mark Richardson of California-based research company Ashima Research.
“Every day and night you have these strong winds that flow up and down the steep topographic slopes. It turns out that a mound like this would be a natural thing to form in a crater like Gale,” Lewis said. “Contrary to our expectations, Mount Sharp could have essentially formed as a free-standing pile of sediment that never filled the crater.”
Even if Mount Sharp were born of wind, it and similar mounds likely overflow with a valuable geological — if not biological — history of Mars that can help unravel the climate history of Mars and guide future missions, Lewis said.
“These sedimentary mounds could still record millions of years of Martian climate history,” Lewis said. “This is how we learn about Earth’s history, by finding the most complete sedimentary records we can and going through layer by layer. One way or another, we’re going to get an incredible history book of all the events going on while that sediment was being deposited. I think Mount Sharp will still provide an incredible story to read. It just might not have been a lake.”