Image by courtesy of NASA

After a four-year journey from Earth which began in September 2007, NASA's ion-engine powered Dawn spacecraft finally entered orbit around the asteroid Vesta early on Saturday 16 July 2011. The 530-kilometre diameter protoplanet is the brightest and second largest object in the main asteroid belt, which is situated between Mars and Jupiter.

The craft will remain in orbit around Vesta for one year and then, in July 2012, will fire its thrusters and depart for the dwarf planet Ceres, the largest object in the asteroid belt. Ceres has a diameter of almost 975 kilometres.