Dawn Spacecraft Discovers Gullies and Evidence of Water on Protoplanet Vesta

NASA's Dawn spacecraft visited the protoplanet Vesta from 2011 to 2013. Now, scientists are getting a closer look at some images, and have discovered that Vesta may have had short-lived flows of water-mobilized material on its surface.

"Nobody expected to find evidence of water on Vesta," said Jennifer Scully, postgraduate researcher, in a news release. "The surface is very cold and there is no atmosphere, so any water on the surface evaporates. However, Vesta is proving to be a very interesting and complex planetary body."

Dawn is currently approaching the dwarf planet series, which is the largest object in the main asteroid belt between Mars and Jupiter. There, it will enter Ceres' orbit on March 6. But as it travels, data from Dawn's exploration of Vesta is continuing to be analyzed by scientists on Earth.

The data reveals that a number of young craters can be found on Vesta. These craters have curved gullies and fan-shaped ("lobate") deposits. The curved gullies, in particular, are significantly different from those formed by the flow of purely dry material.

"We're not suggesting that there was a river-like flow of water," said Scully. "We're suggesting a process similar to debris flows, where a small amount of water mobilizes the sandy and rocky particles into a flow. These features on Vesta share many characteristics with those formed by debris flows on Earth and Mars."

The gullies themselves are fairly narrow at about 100 feet wide. The average length of the gullies are just over half a mile, and Cornelia Crater contains some of the best examples of these curved gullies.

Currently, scientists believe that Vesta has small, localized patches of ice in its subsurface. It's possible that when impacts occur, the heat generated from these impacts is enough to heat the ice and cause these flows.

"If present today, the ice would be buried too deeply to be detected by any of Dawn's instruments," said Scully. "However, the craters with curved gullies are associated with pitted terrain, which has been independently suggested as evidence for loss of volatile gases from Vesta."

The findings reveal a bit more about the protoplanet. That said, studies are still ongoing. Scientists plan to continue to examine the data sent from Dawn to learn more about Vesta as the spacecraft heads toward Ceres.

The findings are published in the journal Earth and Planetary Science Letters.

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