Rosetta sets sights on destination comet
ESA’s Rosetta spacecraft has caught a first glimpse of its destination comet since waking up from deep-space hibernation on 20 January.
These two ‘first light’ images were taken on 20 and 21 March by the OSIRIS wide-angle camera and narrow-angle camera, as part of six weeks of activities dedicated to preparing the spacecraft’s science instruments for close-up study of comet 67P/Churyumov–Gerasimenko.
OSIRIS, the Optical, Spectroscopic and Infrared Remote Imaging System, developed under the leadership of the Max-Planck-Institut für Sonnensystemforschung in Göttingen, Germany, has two cameras for imaging the comet. One covers a wide angle, while the narrow-angle camera covers a smaller field at higher resolution.
OSIRIS is one of a suite of 11 science instruments on the Rosetta orbiter that together will provide details on the comet’s surface geology, its gravity, mass, shape and internal structure, its gaseous, dust-laden atmosphere and its plasma environment.
Rosetta is currently around 5 million kilometres from the comet, and at this distance it is still too far away to resolve – its light is seen in less than a pixel and required a series of 60–300 second exposures taken with the wide-angle and narrow-angle camera. The data then travelled 37 minutes through space to reach Earth, with the download taking about an hour per image.
OSIRIS and the spacecraft’s dedicated navigation cameras will regularly acquire images over the coming weeks to help refine Rosetta’s trajectory in order to bring it steadily in line with the comet ahead of the rendezvous.
Currently, Rosetta is on a trajectory that would, if unchanged, take it past the comet at a distance of approximately 50 000 km and at a relative speed of 800 m/s. A critical series of manoeuvres beginning in May will gradually reduce Rosetta’s velocity relative to the comet to just 1 m/s and bring it to within 100 km by the first week of August.