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Did water once flow on asteroid Vesta?

Elizabeth Howell, News Writer
Jan 23, 2015, 9:58 UTC

Sen—Vesta, one of the largest members of the asteroid belt, has no atmosphere, but probably saw brief spurts of water flow across its surface to produce curved gullies visible in the eyes of NASA's Dawn spacecraft.

The conclusion came after researchers examined the mysterious flows in eight craters, some of which also included deposits that appeared similar in shape to those associated with water-borne deposits of silt on Earth.

Scientists compared the flows to others in 51 craters that were likely created by dust, and saw no notable changes in terrain or slope that could account for the difference. And it also did not look like impact melts observed on other worlds.

"It makes a plausible story. It’s not 100 per cent proven yet, but it hangs together," Jennifer Scully, a postgraduate researcher at the University of California, Los Angeles, told Sen in an interview.

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Curved gullies are visible (inset image) in Cornelia Crater on Vesta. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

So where did the water come from? According to Scully, lead author of a paper on the research, it is likely that the regolith on Vesta is infused with ice a couple of metres below the surface. When a stray piece of space rock crashed into Vesta, this released and melted the ice, which temporarily flowed as water following the impact.

The research assumes that the pressure immediately above the forming crater was a little higher than the usual airless variety. Scully and her collaborators simulated what would happen using beakers of water in a vacuum chamber at the Jet Propulsion Laboratory, which the California Institute of Technology manages for NASA.

The pressure, she said, could be dialled even lower in future experiments to better simulate Vesta's surface. And using flowing water would be a priority, although she acknowledged the practice of mixing in glass beads to simulate regolith particles would be a little messy. "They spray everywhere," she said.

The finding could have applicability on other worlds, but Scully said it would require more examination. While she has not extensively examined the Moon or Mercury for these sorts of features, she said it is possible that impacts could create similar flows on their surfaces.

And when Dawn arrives at Ceres this spring, she said the researchers would be on the lookout for more gullies. It is also possible, however, that Ceres has too much ice for this sort of feature to be possible.

Scully is examining Vesta as a part of her PhD dissertation, which will discuss Vesta's geology. She found the funny features while mapping out sectors of the small body's surface. The research was published in the journal Earth and Planetary Science Letters

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