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Posted: Apr 01, 2014

Osiris has its target in sight

(Nanowerk News) A little more than four months before the arrival of ESA’s spacecraft Rosetta at the comet 67P/Churyumov-Gerasimenko researchers led by the Max Planck Institute for Solar System Research (MPS) have successfully commissioned OSIRIS, the space probe’s scientific imaging system. Since June 2011 the instrument had been switched off in order to save energy during the last part of Rosetta’s ten-year journey through space. Now, OSIRIS is again providing the researchers with images. On the first shots, however, the target comet covers only a fraction of a pixel.
comet 67P/Churymov-Gerasimenko in constellation Ophiuchus
Comet in sight: these images show the comet 67P/Churymov-Gerasimenko in constellation Ophiuchus. The top image was taken with the Wide Angle Camera on March 20 shows a wide field 25 times larger than the diameter of the full moon. The colour composite shows a background of hydrogen gas and dust clouds in the constellation Ophiuchus. The white box indicates the position of the close-up taken with the Narrow Angle Camera (right). Bottom: A zoom into an image taken with the Narrow Angle Camera on March 21. The comet is indicated by the small circle next to the bright globular star cluster M107. The images were taken from about 5 million kilometres distance to the comet. Rosetta was at a distance of approx. 660 million kilometres from Earth.
After the wake-up call on 20 January 2014 tore Rosetta from its more than 30 months of hibernation, now all technical systems and scientific instruments are gradually being awakened to life. In the past days, it was the turn of the orbiter’s scientific imaging system OSIRIS. “The instrument has apparently survived its time-out in good shape. Everything is working as expected”, says Principal Investigator Holger Sierks from the MPS.
The first images of comet 67P/Churyumov-Gerasimenko confirm this. At this point, more than five million kilometres are still separating comet and spacecraft. The comet therefore fills only a fraction of a pixel. Since, in addition, the body is still rather dim, long exposures of 60 to 300 seconds and additional steps of image processing were necessary in order to make it visible.
“Finally seeing our target after a ten year’s journey through space is an incredible feeling”, says Sierks. “These first images taken from such a huge distance show us that OSIRIS is ready for the upcoming adventure. Soon we will see the comet’s activity awakening”, he adds.
During its long journey through the solar system OSIRIS has already demonstrated its capabilities on several occasions: the instrument provided impressive images during flybys of Earth and Mars and was able to scientifically study the asteroids Steins and Lutetia.
In the coming months, OSIRIS will again allow insights into a new world: At first, the shots will help to assess the comet’s activity by its brightness; from mid-July the images will allow to assess the body’s shape.
During the mission, the camera system will visualize structures in the so-called coma, the atmosphere of the comet, and examine the topography and composition of the comet's surface. As of the summer of this year, one of the main focuses will be on the search for a suitable landing site for Rosetta’s lander Philae. Philae is scheduled to touch-down on the comet’s surface in November 2014.
Source: Max Planck Institute for Solar System Research
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