An unmanned NASA probe made history 117 million miles from Earth on Saturday (July 16) when it arrived at the huge asteroid Vesta, making it the first spacecraft ever to orbit an object in the solar system’s asteroid belt.
The Dawn spacecraft entered orbit around Vesta after a four-year chase and will spend about a year studying the huge space rock before moving on to visit another asteroid called Ceres.
Vesta is a huge asteroid about the size of the U.S. state of Arizona, and is also the brightest asteroid in the solar system. It is located in the asteroid belt, a band of rocky objects that encircles the sun between the orbits of Mars and Jupiter.
Vesta is 330 miles (530 kilometers) wide, large enough that astronomers consider it to be a protoplanet. Astronomers do not understand why the asteroid is so bright and hope Dawn will answer that and other mysteries of Vesta.
After studying Vesta in unprecedented detail, the Dawn probe is expected fire up its ion propulsion system to leave orbit and head to Ceres — an object so big it is the largest asteroid in the solar system and officially designated a dwarf planet. Ceres is about 590 miles (950 km) wide. Dawn will arrive at this target in 2012, NASA officials said.
Dawn launched in September 2007 and has covered more than 1.7 billion miles (2.7 billion km) on the voyage to Vesta.
– from scientificamerican.com