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Asteroids are “rocks,” sort of, that orbit the sun. There are hundreds of them, mostly in orbits that lie between Mars and Jupiter. Some asteroids are the size of earth rocks, but Ceres, the largest asteroid, is 950 km (595 mi) in diameter. Vesta is the second most massive at 530 km (331 mi) diameter. Ceres and Vesta are more like miniplanets than rocks. (For comparison, the diameter of the Earth is 7,925 miles).
In September, 2007, NASA (National Aeronautics and Space Administration) launched the $460 million Dawn spacecraft whose mission it is to investigate Vesta and Ceres. Dawn is currently at its closest approach to Vesta and will take 3-4 months photographing and analyzing this little world. Three years from now it will arrive at Ceres and perform similar analyses.
Small meteorites strike the earth all the time. Most are so small that they burn up in the atmosphere. On a given night at most any location, a meteorite (“shooting star”) can be seen to arc across the sky every several minutes. It is estimated that as many as one in 20 of these may be tiny fragments that once were part of Vesta.
The asteroid that struck the Earth and formed the
Barringer Crater in Arizona is determined to have been only about 150 feet in diameter. The Chicxulub Crater, whose perimeter is at the edge of the Yucatan Peninsula, was formed by an asteroid only 6 miles or so in diameter. Some collision models show that an asteroid no bigger than this may have caused the world climate changes that brought about the extinction of the dinosaurs. Neither Ceres or Vesta are going to strike the Earth, of course. They orbit the sun, just like the Earth does.
Preliminary gravity measurements suggest that Vesta has an iron core surrounded by layers of mantle rock and crust, much like the Earth and Mars. Photographs show a pockmarked surface more rugged than the moon and a mountain three times the height of Everest. Around the perimeter of the asteroid is a band of grooves that make it look like it was formed by rolling it along the ground.
The analysis of Vesta should prove quite interesting. Will it have the same relative composition as Earth? If so, what might that mean? What is the age of Vesta as compared to the age of the Earth? What would you consider the most thing to find out?