Dawn spacecraft reveals presence of ice and ammonia on Ceres

Nature : Launched in 2007, NASA’s Dawn spacecraft is currently in orbit around Ceres, one of three known protoplanets in the asteroid belt. Two recently published papers present the first major results from the mission. The first paper centers on some 130 bright spots seen on Ceres’s surface, which researchers say are caused by a mix of frozen water, salt, and rock lying at the bottoms of craters. They appear to glow because of the sublimation of the ice as the Sun rises and light enters the crater and warms its surface. The second study focuses on the discovery of ammonia bound up in clay minerals on Ceres’s surface. Because ammonia is usually found farther out in the solar system, the researchers propose that it may have been brought to Ceres by asteroids and meteorites. Dawn has been refining its path around Ceres and will reach its final mapping orbit, about 385 km above Ceres’s surface, on about 18 December.