Dwarf planet Ceres in the spotlight
Planetary scientists have never seen dwarf planet Ceres from this close up. The German-developed Framing Camera on board NASA's Dawn spacecraft acquired this image on 25 January 2015 from a distance of just 237,000 kilometres. At 43 pixels across, the icy and spherical celestial body reveals details that were not visible in the images previously acquired by the Hubble Space Telescope: "Enormous structures extending across nearly the entire dwarf planet are visible. Although it is not yet possible to determine what happened exactly, it is clear that large-scale processes have transformed the surface of Ceres," says Ralf Jaumann of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), a planetary researcher and member of the Dawn science team. "Each new image will provide us with more clues as to what awaits Dawn when it arrives at Ceres on 6 March this year." The largest celestial body between the orbits of Mars and Jupiter could be concealing an ocean of water under its icy crust.
A series of strangely arranged craters
Until now, the Hubble Space Telescope held the record for obtaining the best views of Ceres; it imaged the dwarf planet between December 2003 and January 2004, and at that time already revealed the existence of different light and dark regions as well as a white spot, which is yet to be understood. Now, the camera on board the Dawn spacecraft is in the lead: "The resolution of our images exceeds that of previous Hubble images by more than 30 percent," says Jaumann. In the celestial body's southern hemisphere, some very dark features can be seen in an overall darker region. "A global structure, which is suspected to be a number of large, oddly arranged impact craters is easily identifiable." The well-known bright spot can be seen about 90 degrees away from this structure.
The results of the Dawn mission could allow planetary researchers to learn more about the formation of the planets 4.5 billion years ago. "Asteroids are the building blocks of a planet that never came to be." The gravitational forces in the vicinity of Jupiter ensured that the individual fragments repeatedly broke apart and could not form a complete planet. The result is the asteroid belt between Mars and Jupiter, with its major bodies Vesta, Pallas and Ceres – three of the best-preserved protoplanets in the Solar System.
The Dawn spacecraft sent more than 30,000 images, 18 million spectral measurements and other scientific data to Earth during its 2011/2012 visit to Vesta. This body, with a mean diameter of 525 kilometres surprised everyone with two giant impact basins, deep gorges and a mountain twice as high as Mount Everest. In September 2012, the spacecraft left Vesta and has been traveling through space using an ion propulsion system. Its next target, Ceres, is an icy object at the outer reaches of the asteroid belt, where the influence of the Sun – some 415 million kilometres away – is not very great.
Like an insect in amber
Ceres will be the first dwarf planet to be investigated by a spacecraft from orbit. With a diameter of almost 1000 kilometres, it is the largest body in the asteroid belt. In fact, in 2006 the International Astronomical Union moved it into the category of 'dwarf planet'. Jaumann believes that Ceres could be concealing a secret under its icy crust – a thick layer of water. "We have never flown to such a celestial body," he says. "The earliest stages of planet formation are probably preserved in Ceres – like an insect in amber tells us about prehistoric creatures."
The Dawn 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 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.