Water may have been flowing over the surface of Mars as recently as 1.25 million years ago, according to a new study that examined gullies and fan-shaped deposits on the Martian landscape and determined that they were formed by melting ice. There probably wasn’t much water, explains lead researcher Samuel Schon: “You never end up with a pond that you can put goldfish in…. But you have transient melt water. You had ice that typically sublimates. But in these instances it melted, transported, and deposited sediment in the fan. It didn’t last long, but it happened” [BBC News].
NASA‘s Mars Reconnaissance Orbiter was able to distinguish evidence of water-borne sediments being carried down from high ground and deposited in low-lying alluvial fans [Telegraph]. While previous research had raised the possibility that Martian gullies were carved by avalanches of sand, the sharp new images discredit the theory of drifting sands, and the classic alluvial pattern of the delta does not fit with sedimentary shifts, Schon says. Jack Holt, a geophysicist at the University of Texas at Austin, agrees “melting an ice deposit caused by an ice age seems like a more feasible scenario” [Scientific American].
Researchers think that Mars may have had oceans several billions of years ago, and say that wobbles in Mars’s rotational axis may have caused drastic climate changes and ice ages throughout the planet’s history. To determine when the gullies and fan-shaped deposits formed, researchers studied four distinct lobes that made up the alluvial fan. Schon was able to determine that the lobes were created at different times and could tell which was the oldest because it was pockmarked with craters, while the younger lobes were left relatively unblemished. (The longer a surface has been exposed, the more meteorites have had a chance to leave their mark) [SPACE.com].
Researchers traced the pattern of pockmarks on the oldest lobe, and realized that the small craters were the result of a large meteorite strike about 60 miles away that kicked up a spray of rocks. In their report, to be published in the journal Geology, researchers say that the large, primary crater formed by the meteorite dates from 1.25 million years ago, indicating that the three unblemished lobes were formed by flowing water sometime after that.
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Image: NASA/JPL/University of Arizona