The Dawn space probe, which was launched by NASA in 2007, reached the dwarf planet Ceres and started orbiting it earlier today. According to the press release, Dawn is the first spacecraft to be placed into orbit around a dwarf planet. Ceres is located in an orbit between those of Mars and Jupiter, so it isn’t that far away by astronomical scales. One of the reasons why it took so long for the probe to get there is that it already flew by Vesta, another dwarf planet. While in orbit, Dawn will study Ceres with a number of instruments, including a radiation detector, a light spectrometer, and a camera operating at visible wavelengths. The scientific payload was produced by various agencies in the US and Europe. Scientists working on the mission hope to learn about things like the dwarf planet’s interior composition, surface composition, and gravitational fields.