September 20, 2012
Evidence Of Hydrated Minerals Found On Vesta By Dawn Spacecraft
Watch the Video: Hydrogen Hot Spots on Vesta
Lee Rannals for redOrbit.com - Your Universe Online
Dawn did not find actual water ice at Vesta, but it did reveal signs of hydrated minerals delivered by meteorites and dust to the asteroid.
"The source of the hydrogen within Vesta's surface appears to be hydrated minerals delivered by carbon-rich space rocks that collided with Vesta at speeds slow enough to preserve their volatile content," Thomas Prettyman, the lead scientist for Dawn's Gamma Ray and Neutron Detector (GRaND) and a leader of the team, said in a prepared statement.
Two papers were published in Science based on observations from the low-altitude mapping orbit of Dawn, showing that easily evaporated materials, or volatiles, have colored Vesta's surface in a broad swath around its equator.
The features seen in the observations mark some of the asteroid's surface where the volatiles released from hydrated minerals boiled off.
In one paper, led by Brett Denevi, the authors describe the presence of pitted terrain created by the release of the volatiles.
Scientists thought it might be possible for water ice to survive near the surface around the asteroid's poles. However, the strongest evidence for hydrogen in the latest data came from regions near the equator, where water ice is not stable.
In some cases, when other space rocks collided with Vesta, the heat from the collisions converted the hydrogen bound to the minerals into water, which evaporated. The holes that were left as the water escaped stretch as much as 0.6 miles across and go down as deep as 700 feet.
"The pits look just like features seen on Mars, but while water was common on Mars, it was totally unexpected on Vesta in these high abundances," Denevi, a Dawn participating scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said. "These results provide evidence that not only were hydrated materials present, but they played an important role in shaping the asteroid's geology and the surface we see today."
Data from Dawn's Gamma Ray and Neutron Detector (GRaND) are the first to detect measurements describing the elemental composition of Vesta's surface. The spacecraft's instruments help to determine the ratios of iron to oxygen and iron to silicon in the surface material.
The new findings confirm the connection between Vesta and a class of meteorites found on Earth called the Howardite, Eucrite and Diogenite meteorites.
More volatile-rich fragments of other objects have been identified in these meteorites as well, supporting the idea that the volatile-rich material was deposited on Vesta.
“Where did the hydrogen from Vesta´s surface come from? We ruled out the wind of charged hydrogen particles streaming off the Sun as a source, as well as water ice within the top few feet of Vesta´s surface,” Prettyman said. “The hydrated minerals appear to be delivered by carbon-rich space rocks that collided with Vesta at speeds slow enough to preserve their volatile content.”