The last place you'd expect to find signs of water erosion is in the Asteroid Belt, but researchers from NASA's Jet Propulsion Laboratory (JPL) say that data collected during the Dawn spacecraft's visit to the protoplanet Vesta indicates that it not only once had water, but that it formed gullies and other erosion features on its surface.
Vesta was originally thought to be bone dry, but images and instrument readings from the unmanned Dawn probe's visit to Vesta, during which is orbited the protoplanet (or giant asteroid) from 2011 to 2013, indicate that water may once have been present on the asteroid and that it had a part to play in forming its features. In particular, Dawn sent back images of young craters with curved gullies and fan-like deposits. About 100 ft (30 m) wide and stretching half a mile (900 m), these gullies are especially prominent in the 9 mi (15 km) wide Cornelia Crater.
The JPL team is quick to point out that what happened wasn't flowing rivers running across the face of Vesta. The extreme cold, hard vacuum and extremely weak gravity wouldn't allow liquid water to exist on the surface – once exposed above a certain temperature, it would immediately sublimate into gas. Instead, the water had a more indirect role to play.
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