Rosetta spacecraft sets sights on destination comet

ESA's Rosetta spacecraft caught a first glimpse of its destination comet since waking up from deep-space hibernation on January 20 this year.

OSIRIS, the Optical, Spectroscopic and Infrared Remote Imaging System, developed under the leadership of the Max-Planck-Institut fur Sonnensystemforschung in Gottingen, 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.

Rosetta has been travelling through the solar system for 10 years, and will finally arrive at the comet in August this year. It first imaged the comet in a long exposure of over 13 hours from a distance of 163 million kilometers, three years ago, before entering deep-space hibernation.

Rosetta is currently around 5 million kilometers 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- to 300-second exposures taken with the wide-angle and narrow-angle camera.

Between May and August the 4-km-wide comet will gradually 'grow' in Rosetta's field of view from appearing to have a diameter of less than one camera pixel to well over 2,000 pixels-equivalent to a resolution of around 2 m per pixel-allowing the first surface features to be resolved.

These early observations will allow the rotation rate and the shape of the nucleus to be better understood, crucial for planning maneuvers around the comet. An initial assessment of the comet's activity will also be possible.