Petersburg is a eucrite (achondrite) whose fall was witnessed August 5th of 1855, in Tennessee.
Eucrites are the most common type of achondrite meteorite falls (vs. finds) and are believed to form from cooling of magma on the surface of the Asteroid 4-Vesta; the number 4 refers to Vesta being the fourth asteroid ever discovered, in March of 1807, by German astronomer Heinrich Wilhelm Olbers.
In September 2007, NASA launched the Dawn mission to study Vesta and the dwarf planet Ceres to provide insight into the formation and evolution of solid bodies in the early solar system, using a visible camera, a visible and infrared mapping spectrometer, and a gamma ray and neutron spectrometer.
After a year orbiting Vesta, Dawn is now headed to a rendezvous with the dwarf planet Ceres, the largest object in the main asteroid belt, in 2015. Dawn is one of NASA's Discovery class missions. Click here for the latest Vesta images and Dawn mission updates!