Dawn reaches Ceres
Dawn space probe captured by the dwarf planet’s gravitational field
The signal was received by the ground station at 14.36 hours Central European Time: Dawn was captured by the gravitational field of the dwarf planet Ceres and thus became the first spacecraft in history to enter into orbit around two different planetary bodies in succession. Back in 2011, Dawn reached the asteroid Vesta and orbited it for over one year. For the scientists at the Max Planck Institute for Solar System Research in Göttingen, the critical phase of this mission now begins. With the help of their on-board camera system, they aim to produce – among other things – colour maps of Ceres and in this way uncover information about ice on the dwarf planet.
The US space probe Dawn is very well equipped for its expedition to the asteroid belt between the orbits of Mars and Jupiter: no fewer than three scientific instruments will be used to elicit the secrets of the dwarf planet Ceres. In addition to a system for detecting gamma waves and neutrons and an infrared spectrometer, they include a camera system which was developed under the direction of the Max Planck Institute for Solar System Research in Göttingen.
The camera system already delivered initial views of the dwarf planet during the approach phase in recent months. The real photo shoot is set to begin in the weeks to come: the scientists want to record at least 10,000 images, some of which will make structures of just 40 metres in size visible.
“We will have a lot to do over the next year and a half but we have all the resources we need and a robust timetable for meeting our scientific objectives,” says Chris Russell from the University of California in Los Angeles (USA), principal investigator of the mission. Moreover, as he adds, the team is “very excited and full of anticipation.”
The mission’s goals include photographing the dwarf planet in detail. The camera system is fitted with seven colour filters. These enable the scientists to filter certain wavelengths out of the light reflected by Ceres into space and, based on this, to track down the characteristic fingerprints of certain substances. These can be used to determine the mineralogical composition of the planet’s surface and the resulting information can then be presented on colour maps.
“Many of these mineralogical differences cannot be seen with the naked eye,” says Andreas Nathues from the Max Planck Institute for Solar System Research, lead investigator of the framing camera team. “The colour maps reveal the real history of Ceres and contain information about its formation and evolution that is not found in purely topographical maps.”
In the case of the asteroid Vesta, the Dawn mission’s initial destination, such mineralogical tests were able to help to explain the planet’s internal structure, for example. The colour maps showed that the mineral olivine – a typical component of the internal solid mantle of many planets – only arises close to small impact craters. This indicates that it was introduced from outside and does not originate from Vesta’s own mantle. This led to the conclusion that the asteroid’s mantle must lie under a rock crust that is at least 30-80 kilometres thick and, therefore, far deeper than previously assumed.
The researchers expect that the colour contrasts for Ceres will be weaker than those obtained for Vesta. Nevertheless, it is expected that the colour maps will enable them to track down the ice suspected to lie beneath the dwarf planet’s surface.
The team will have to wait a few weeks for the next images to arrive from Ceres. Because Dawn is entering an orbit around Ceres from a side that does not face the sun, the camera system is currently directed at a dark side of the planet. The most recent photos which were taken four days in advance of today’s arrival merely show Ceres as a slim crescent. The next images are expected to start arriving from mid-April.
BK / HOR
The Dawn Mission is headed by the Jet Propulsion Laboratory (JPL) of the American space agency NASA. JPL is a department of the California Institute of Technology in Pasadena. The University of California in Los Angeles is responsible for the scientific part of the mission. The camera system aboard the spacecraft was developed and built under the direction of the Max Planck Institute for Solar System Research in Göttingen in collaboration with the Institute of Planetary Research of the German Space Center (DLR) in Berlin, and the Institute of Computer and Network Engineering in Braunschweig. The camera project is supported financially by the Max Planck Society, the DLR and NASA/JPL.