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Posted: July 7, 2008 ESA’s comet-chasing Rosetta spacecraft has awoken from hibernation to prepare for its encounter with rare asteroid (2867) Steins on 5 September as it speeds through the Solar System en route to comet 67/P Churyumov-Gerasimenko, where it will make the first ever landing attempt on a comet.
Artist impression of Rosetta swinging by the Earth in one of its gravity assist maneuvers. Image: ESA/C.Carreau. Although Rosetta was launched in March 2004, it has only made a small dent in its epic ten year journey to comet 67/P Churyumov-Gerasimenko. But it is being kept busy along the way, and is currently being pin-balled around the inner Solar System in a series of gravity-assist maneuvers, having already whipped around Earth twice and Mars once, with the last Earth flyby to occur in November 2009. The next two milestones in the spacecraft’s journey will be a rendezvous with asteroid (2867) Steins in September this year and (21) Lutetia in June 2010. Rosetta was placed in hibernation earlier this year as it careered around the Sun, but was summoned from its slumber a few days ago in preparation for its encounter with (2867) Steins. Closest approach to the asteroid is scheduled for 20:37 on September 5, where it will zoom past the asteroid at a speed of 8.6 kilometres per second and a distance of 800 kilometres. (2867) Steins is a relatively rare type of asteroid and although it has been classified from ground-based observations as an E-type asteroid, composed mainly of silicates and basalts, its properties are not known in any great detail. The knowledge gained from the Rosetta flyby will help planetary scientists learn more about the composition and evolution of E-type asteroids, as well as providing supplementary data to help interpret future ground- based observations of asteroids. Many of the observations planned for the flyby are designed to test the range of instruments onboard Rosetta, including measurements of its physical and chemical properties, rotation, and interaction with the solar wind and surrounding environment.
Rosetta took images of Mars during the February 2007 flyby of the red planet, although here (left) it appears blue as it is imaged in ultraviolet through the OH colour filter, intended for the indirect detection of water when it reaches the comet. The image shows detail and structure in the Martian atmosphere, visible more clearly in the processed image on the right. Images: ESA/MPS for OSIRIS Team MPS/UPD/ LAM/ IAA/ RSSD/ INTA/ UPM/ DASP/ IDA. Rosetta will finally reach comet 67/P Churyumov-Gerasimenko in May 2014 and will attempt the amazing feat of landing on the comet’s surface six months later, where it will study the composition and structure of the comet’s nucleus. The onboard instruments are designed to relay everything from the chemistry of the surface, to its strength, density, texture, porosity, ice phases and thermal properties, giving scientists a detailed, global picture of a comet's nucleus. Even more ambitious is the Sampling Drilling and Distribution Device, which will drill more than 20 centimetres into the surface, collect samples and deposit them in different ovens or deliver them to the lander for microscope inspection. Rosetta will enter orbit around the comet and stay with it as it journeys in towards the Sun.
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