Vesta has always been thought to be completely dry, with surface pressure and low temperatures making it impossible for the protoplanet to retain water. That was until a new study showed that Vesta once had water albeit short-lived.
NASA's Dawn spacecraft was able to visit Vesta between 2011 and 2013. During that time, researchers were able to gather data showing that the proplanet cultivated many processes that were once believed to be distinct in planets. Through the spacecraft, researchers identified several young craters with fan-shaped deposits and curved gullies on Vesta, publishing their findings in the journal Earth and Planetary Science Letters.
According to Jennifer Scully from the University of California Los Angeles, the curved gullies bore markings significantly different from what would normally form if dry material flowed. Researchers are not saying that there was enough water on Vesta to simulate the flow of a river but that there was still enough to help rocky and sandy particles along. They do believe, however, that the combination of water and solid particles formed the gullies discovered, quite similar to a process that would normally be present on Earth or Mars.
Fairly narrow, the gullies are about 100 feet wide and a little over a mile in length on average. Some of the best examples of fan-shaped deposits and curved gullies on Vesta are found in the Cornelia Crater.
Researchers theorize that the curved gullies were brought about by small patches of ice localized on Vesta's subsurface. Where the ice came from is not clear but it is possible that the protoplanet was hit by a comet and the resulting impact left ice on the protoplanet's subsurface. Another impact formed the crater, heating up ice patches which released water.
"If present today, the ice would be buried too deeply to be detected by any of Dawn's instruments," explained Scully. She also added though that the craters' curved gullies are usually characterized by pitted terrain, considered to be independent evidence that volatile gases were lost from Vesta.
Craters showing curved gullies don't look to be older than several hundred million years, and is still considered young though Vesta is already 4.6 billion years old. Experiments at the NASA Jet Propulsion Laboratory indicate that the curved gullies formed before water evaporated from the protoplanet's subsurface.
Aside from Scully, co-authors for the study include: Lucille Le Corre, Christopher Russell, Vishnu Reddy, An Yin, Carol Raymond, Ralf Jaumann, Elizabeth Carey, Harry McSween and Julie Castillo-Rogez.
