The Dawn spacecraft that has been orbiting the asteroid Vesta since July continues to send back excellent pictures of a member of our solar system that is looking more and more interesting. For example, it now looks as if Vesta has an iron core and has had ancient basaltic lava flows on its surface. It has a mountain bigger than Earth’s largest and almost as tall as Olympus Mons on Mars, the tallest in the solar system. Moreover, the surface is heavily pocked with craters billions of years old, making it look rather like the moon.
All this came out of a session yesterday at the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences in Nantes, France.
Though Vesta measures only about 330 miles in diameter, Space.com, which has a fine roundup today of the latest on Vesta, quotes Dawn’s P.I. calling the asteroid “the smallest terrestrial planet.” The piece, oddly unbylined, does not elaborate on that characterization, which is curious given the flap a few years ago over whether Pluto should be called a planet. Vesta has been considered a possible dwarf planet, but no official designation seems to have been set.
Vesta’s iron core presumably indicates that its mass was great enough to create the internal heat required to melt its substance, allowing iron to separate out and sink to the center. Startlingly sharp images of Vesta, some accessible on the Web site, show its shape to have developed a good part of the way toward becoming spherical. It also shows regions that look as if some ancient collision had smashed away big chunks.
Ron Cowen, writing in Nature.com, goes beyond the official report to divulge other findings that he says the Dawn researchers deemed “not quite ready for prime time.” Cowen, nonetheless, takes readers inside the lab meeting. Among the suggestive interpretations of new data: The asteroid belt once “was a much more crowded and rowdy place” with crashes and rebounds galore; Vesta was “walloped” from several directions by giant objects in at least four different cataclysmic events; that the asteroid belt once extended much closer to the Sun; and that a bashed region on one side of Vesta could be the source of many meteorites recovered on Earth.
-Boyce Rensberger
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