Above the north pole of dwarf planet Ceres
White patches on the dwarf planet Ceres have fascinated scientists since their discovery. Now, the Dawn orbiter has transmitted new images looking vertically down on to the dwarf planet's north pole, showing two unusual patches clearly distinct from their darker surroundings. They are located in a crater with a diameter of roughly 92 kilometres. "These extraordinarily light patches have not changed since we started observing them," says Ralf Jaumann, a planetary researcher at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and a member of the Dawn mission's Framing Camera team. "The phenomenon is quite exciting, and it is certain to give us a few surprises."
The discovery of white patches on Ceres is a sensation, as nothing similar has been observed on any other body in the Solar System thus far. "Their origin is a mystery. At the moment, we are unable to say anything about their structure or composition," explains Jaumann. "They are just rather bright points, which are probably less than four kilometres across." In its current position, the Dawn orbiter is still too far away to provide any clear indications of their shape. These images were acquired from a distance of 22,000 kilometres on 15 April 2015.
Orbiting Ceres ever closer
After arriving at the dwarf planet, Dawn initially disappeared behind the side of Ceres facing away from the Sun, and was unable to acquire any additional images. The orbiter emerged again on 10 April 2015, and has been busy tightening its orbit, drawing ever closer from a distance of 42,000 kilometres – before reaching an altitude of just 13,500 kilometres on 23 April 2015. "That is when the science phase will begin. We will be able to acquire images with a resolution of one or two kilometres per pixel," explains Jaumann. "Perhaps then, we will be able to provide more meaningful information on Ceres' unusual white patches." In June, Dawn will be close enough to the dwarf planet to acquire images with a resolution of just 400 metres per pixel.
Dawn is taking planetary researchers on a flight into the formation and evolution of the Solar System. When the planets were forming, 4.5 billion years ago, Jupiter's gravity ensured that the asteroids 'stuck' during this process, preventing them from proceeding to form planets. These partially-formed planets preserve the very beginnings of the Solar System. NASA's Dawn orbiter visited the low-water-content asteroid Vesta from 2011 to 2012. In contrast, the dwarf planet Ceres, situated further from the Sun and therefore icy, allows the scientists to examine a decidedly water-rich celestial body; researchers have conjectured that there may be an ocean beneath its crust. Ceres advanced from its previous classification as an asteroid to become one of the new dwarf planets in 2006. At almost 1000 kilometres in diameter, it is the largest object in the asteroid belt between Jupiter and Mars.
The mission
NASA's Jet Propulsion Laboratory (JPL) in Pasadena manages the Dawn mission; JPL is a division of the California Institute of Technology. The University of California, Los Angeles, is responsible for the overall Dawn mission science. The camera system on the spacecraft was developed and built under the leadership of the Max Planck Institute for Solar System Research in Göttingen, Germany, in collaboration with the DLR Institute of Planetary Research in Berlin and the Institute of Computer and Communication Network Engineering in Braunschweig. The Framing Camera project is funded by the Max Planck Society, DLR, and NASA/JPL.