September 26, 2012
Water May Have Been Deposited On Vesta Asteroid Long Ago
Lee Rannals for redOrbit.com — Your Universe Online
Astronomers suggest that water may have been delivered to Vesta through a build-up of small particles during an epoch when the Solar System was rich in dust.The team presented their research at the European Planetary Science Congress in Madrid on Wednesday, offering up a radically different hypothesis from the way in which hydrous materials are deposited on other cosmic objects.
Using data from NASA's Dawn mission, the team found that Vesta's surface shows distinct areas enriched with hydrated materials.
"These regions are not dependent on solar illumination or temperature, as we find in the case of the Moon," De Sanctis, of the Institute of Astrophysics and Space Planetology in Rome, said in a press release. "The uneven distribution is unexpected and indicates ancient processes that differ from those believed to be responsible for delivering water to other airless bodies, like the Moon."
The team studied data from Dawn's visible and infrared (VIR) mapping spectrometer, showing large regional concentrations of hydroxyl clearly associated with geological features like ancient, highly-cratered terrains and the Oppia crater.
Hydroxyl on the surface of the Moon is thought to be created by the interaction of protons from the solar wind with the lunar regolith, or extraterrestrial soil.
Highest concentrations are found in areas near the lunar poles, and in permanently shadowed craters where it is cold.
The distribution of hydroxyl on Vesta is not dependent on significant shadowing or unusual cold temperatures, and it is also stable over time. The hydroxyl-rich regions on the asteroid correspond to its oldest surfaces, and its detections are weak or absent, suggesting the delivery of hydroxyl is not an ongoing process.
Evidence from VIR suggests that Vesta's hydroxyl was delivered by small particles of primitive material, less than a few centimeters in diameter. This period may have occurred during the primordial solar system, or during the Late Heavy Bombardment, which is when collisions would have produced a large amount of primitive material dust.
The Oppia Crater is hydroxyl-rich, but not covered with the primitive material, which suggests that there is more than one mechanism at work for depositing hydroxyl on Vesta's surface.
"The origin of Vesta´s hydroxyl is certainly complex and possibly not unique: there could be various sources, like formation of hydroxyl actually on Vesta, in addition to the primordial impactors," Sanctis said in the press release. "Vesta is providing new insights into the delivery of hydrous materials in the main asteroid belt, and may offer new scenarios on the delivery of hydrous minerals in the inner Solar System, suggesting processes that may have played a role in the formation of terrestrial planets."