Planetary scientists thought they knew what to expect when NASA's Dawn spacecraft returned the first close-up portrait of the giant asteroid Vesta last month. Fuzzy images from the Hubble Space Telescope (HST) taken in 1996 seemed to show that something had taken a big bite out of the asteroid's south polar region.
The crater was posited as the source of Vesta-like fragments that populate the asteroid belt, and of a surprisingly large fraction of the meteorites found on Earth.
But seconds after viewing the first image, Peter Thomas of Cornell University in Ithaca, New York, shot off an e-mail to other members of the team: "Looks like HST results were fantasy!"
Thomas later realized he had misjudged Dawn's location when he sent that e-mail, but his words give an idea of scientists' surprise. Vesta's huge depression isn't like those of most impact craters: it is ringed by a wall for only about half its circumference, says Dawn team member Paul Schenk of the Lunar and Planetary Institute in Houston, Texas. It also has a large rounded mound in its middle, rather than the usual conical uplift.
To read the rest of the article, click here.
