First orbit of an object in the asteroid belt

On 16/07/2011, NASA’s Dawn spacecraft entered orbit around the protoplanet 4 Vesta, becoming the first mission to orbit an object located in the main asteroid belt between Mars and Jupiter. The spacecraft achieved gravitational capture after gradually matching Vesta’s velocity using its ion propulsion system. Unlike traditional orbital insertions, Dawn spiraled into orbit without a large engine burn, allowing it to begin detailed mapping and scientific observations of the asteroid. Vesta, measuring about 525 kilometers in diameter, is one of the largest bodies in the asteroid belt and is considered a protoplanet formed early in solar system history. Although NASA’s NEAR Shoemaker spacecraft had previously orbited asteroid 433 Eros in 2000, Eros is classified as a near Earth asteroid rather than a main belt object. Dawn’s arrival at Vesta therefore marked the first orbital exploration of a main belt asteroid. Once in orbit, the spacecraft conducted global mapping, measured gravity, and analyzed surface composition. Observations revealed large impact basins, including the Rheasilvia basin at Vesta’s south pole, along with a central peak rising more than 20 kilometers above surrounding terrain. Dawn remained at Vesta until September 2012, collecting data from multiple orbital altitudes. After completing its study, the spacecraft departed using ion propulsion and traveled onward to Ceres. On 06/03/2015, Dawn entered orbit around the dwarf planet Ceres, becoming the first spacecraft to orbit two different extraterrestrial bodies. The mission demonstrated long duration ion propulsion and provided detailed comparisons between two large bodies in the asteroid belt.