NASA’s Dawn spacecraft entered orbit around Ceres at approximately 7:40 ET on the morning on March 6, the first time a spacecraft has orbited a dwarf planet. Ceres is the largest asteroid and the first discovered, on January 1, 1801. Originally classified as a planet, it was re-classified as an asteroid when it was clear that it was only one of many objects between Mars and Jupiter. Dawn previously orbited Vesta, the second largest asteroid and the fourth discovered, from 2011-2012. This is the first time a spacecraft went into orbit around two objects outside the Earth-Moon system. Dawn will begin its study of Ceres next month and will remain in orbit until 2016.
The ESA’s Herschel Space Observatory has detected signs of water vapor being ejected from Ceres, the largest asteroid. The two plumes, which are in different regions of the asteroid, are probably sublimation of ice into clouds of vapor or ice volcanoes. Scientists have believed that Ceres might have water for more than thirty year, but this was the first proof.