This computer-enhanced picture shows the Vesta topography derived from Hubble Space Telescope images. The distinctive crater shape, with a central peak, is similar to much smaller craters formed on the moon. Black areas represent low altitude, while white areas show high altitude. This crater may be the site of origin of 6 percent of all meteorites that reach the Earth. Vesta is located in the asteroid belt between Mars and Jupiter. Peter Thomas/Cornell University
Proving that even minor planets can survive cosmic fender-benders, astronomers using the Hubble Space Telescope have discovered an enormous crater with an estimated diameter of 285 miles and a depth of about 8 miles on the asteroid Vesta. The researchers' findings are published in an article in the recent issue of the journal Science (Sept. 5).
Even in cosmic terms, the scientists admit the crater is a humdinger of a dinger.
"When I saw the raw pictures from the Hubble Space Telescope, it was like, 'wow!'" said Peter C. Thomas, Cornell senior research associate in the Center for Radiophysics and Space Research. He explained the crater is big enough to have spewed enough impact debris to be a source of special types of meteorites and other Vesta-like objects.
"Clearly, when we got the pictures, the southern area of Vesta was mangled. These photos confirmed it was just one crater," Thomas said.
The crater, roughly the diameter of Ohio, was found using the Hubble Space Telescope's Wide Field Planetary Camera 2.
Vesta, at about 330 miles in diameter itself, is not the biggest asteroid, but it is the brightest. It was discovered by Wilhelm Olbers, a German astronomer, in 1807.
News of the Vesta crater's discovery is published in the Science article, "Impact Excavation on Asteroid 4 Vesta: Hubble Space Telescope Results," co-authored by Thomas and Richard P. Binzel of the Massachusetts Institute of Technology, Michael J. Gaffey of Rensselaer Polytechnic Institute, Alex D. Storrs and Eddie N. Wells of the Space Telescope Science Institute in Baltimore, and Benjamin H. Zellner of Georgia Southern University.
Trailing Vesta through space is a family of smaller asteroids with geochemical makeups similar to the larger body. With the discovery of Vesta's crater, astronomers now deduce the smaller objects some small fragments of which eventually reach Earth as meteorites originated from the blast from the ancient past.
Researchers believe the trailing chips off the old asteroid account for a low percentage of the volume that was blasted out. However, the minor planet is believed to be the origin of basaltic achondrite HED meteorites, which have evidence of a variety of volcanic materials. These materials are similar to the basalts that cover the Earth's ocean floors and many surface volcanoes, such as on Hawaii. The distinctive meteorites comprise 6 percent of all meteorites that fall to the Earth. Thus, it is possible that Vesta supplied a noticeable fraction of the meteoritic material that has reached Earth in recent times.
Until last year, getting a good portrait of Vesta was difficult. The research team using the space telescope managed to get the best images ever of Vesta in May 1996 because of its close proximity 110 million miles to Earth. While the Hubble Space Telescope travels with the Earth around the sun, Vesta also rotates and moves around the sun, making it tricky to obtain images of the minor planet's southern side, Thomas said.
Astronomers also learned the crater has a central peak, which is about 8 miles high and looks like a raised bull's eye.
"The moon has craters with raised peaks, too. But Vesta has one-seventh the gravity of the moon," Thomas said. "Now we have tangible, physical evidence that to get craters with raised, central peaks on low-gravity objects like Vesta, we need large objects to make big collisions."