Rosetta's First Glimpse of the Comet
In these first images comet Churyumov-Gerasimenko appears as a single point of light covering only a few pixels. “But the pictures already give us a good idea of where we are headed”, says Dr. Holger Sierks from MPS, OSIRIS Lead Investigator. “In addition, they are a remarkable proof of the camera’s performance. We had not expected to be able to create first images from so far away.”
Comet Churyumov-Gerasimenko is extremely faint. Its brightness is approximately a million times less then that of the faintest star that can be discerned from Earth with the naked eye. Astronomers studying the comet from Earth use the European Southern Observatory’s Very Large Telescope in Chile, one of the world’s most powerful telescopes with a main mirror diameter of eight meters. OSIRIS’s mirror measures only approximately ten centimeters in diameter.
In order to make the comet visible despite these challenges, an exposure time of 13 hours was necessary. “All in all, we took 52 images with OSIRIS, each exposed for 15 minutes”, explains Dr. Colin Snodgrass from MPS, responsible for data processing. Since within a period of a few hours the comet moves relative to the background of fixed stars, the first step was to align all of the images and correct for this motion. After further refined steps of data processing (for example subtracting the fixed stars) the researchers were able to catch a first glimpse of their destination.
Before they get a chance at a second glimpse, it will, however, be a long wait. The systems on board Rosetta will be powered down today for approximately three years. In this way the solar panel powered spacecraft saves energy while it is far from the Sun -- until it reawakens in the spring of 2014 and takes a next look at “its” comet.
The spacecraft Rosetta has been en route to comet Churyumov-Gerasimenko since 2004. OSIRIS, the scientific camera system on board, was developed and built under the lead of the MPS in cooperation with a team bringing together members of six European countries. It consists of a wide- and a narrow-angle camera. The camera system is operated by scientists from MPS.