Washington — Though generally thought to be quite dry, roughly half of the giant asteroid Vesta is expected to be so cold and to receive so little sunlight that water ice could have survived there for billions of years, according to the first published models of Vesta’s average global temperatures and illumination by the sun.
“Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface,” said Timothy Stubbs of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Stubbs and Yongli Wang of the Goddard Planetary Heliophysics Institute at the University of Maryland published the models in the January 2012 issue of the journal Icarus.
So far, Earth-based observations suggest that the surface of Vesta is quite dry. However, the Dawn spacecraft is getting a much closer view. Dawn is investigating the role of water in the evolution of planets by studying Vesta and Ceres, two bodies in the asteroid belt that are considered remnant protoplanets — baby planets whose growth was interrupted when Jupiter formed.
Dawn’s mission to Vesta and Ceres is managed by NASA’s Jet Propulsion Laboratory in Pasadena, California. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are partners on the mission team.
The presence or absence of water ice on Vesta tells scientists something about the tiny world’s formation and evolution, its history of bombardment by comets and other objects, and its interaction with the space environment. Because similar processes are common to many other planetary bodies, including the moon, Mercury and other asteroids, learning more about these processes has fundamental implications for understanding the solar system as a whole. This kind of water ice is also potentially valuable as a resource for space travelers who may someday further explore the solar system.
Dawn is looking for water using the gamma ray and neutron detector (GRaND) spectrometer, which can identify hydrogen-rich deposits that could be associated with water ice. The spacecraft recently entered a low orbit that is well suited to collecting gamma ray and neutron data.
“Our perceptions of Vesta have been transformed in a few months as the Dawn spacecraft has entered orbit and spiraled closer to its surface,” says Lucy McFadden, a planetary scientist at NASA Goddard and a Dawn mission co-investigator. “More importantly, our new views of Vesta tell us about the early processes of solar system formation. If we can detect evidence for water beneath the surface, the next question will be is it very old or very young, and that would be exciting to ponder.”
“The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta,” Stubbs said. “Hopefully, we’ll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta’s regolith. This is an important and exciting time in planetary exploration.”