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Rosetta's comet is mapped and dusted

Jenny Winder, News Writer
Sep 10, 2014, 14:46 UTC

Sen—Scientists have produced the first map of comet 67P/Churyumov-Gerasimenko, the comet that the European Space Agency's Rosetta spacecraft is orbiting. And today they followed up with an impressive "selfie" showing the probe and its comet.

By analyzing images of the comet's surface taken by OSIRIS, Rosetta's scientific imaging system, the ESA scientists have allocated several distinct regions, each of which is defined by special morphological characteristics.

"Never before have we seen a cometary surface in such detail", says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. In some of the images, one pixel corresponds to 75 centimetres scale on the nucleus. "It is a historic moment, we have an unprecedented resolution to map a comet," he adds. 

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Another treat from Rosetta is this amazing "selfie" taken by a camera on its Philae lander, showing the spacecraft and the nucleus of the comet in the background. It was taken on 7 September at a distance of about 50 km from the comet. Image credit: ESA/Rosetta/Philae/CIVA

"This first map is, of course, only the beginning of our work", says Sierks. "At this point, nobody truly understands how the morphological variations we are currently witnessing came to be." 

With areas dominated by cliffs, depressions, craters, boulders or even parallel grooves, 67P displays a multitude of different terrains. While some of these areas appear to be quiet, others seem to be shaped by the comet's activity. As OSIRIS images of the comet's coma indicate, the dust that 67P casts into space is emitted there. 

Rosetta has also had its first encounter with dust from the comet. An image of the first grains collected by the COSIMA instrument when Rosetta was at a distance of less than 100 km from 67P's nucleus has been released.

On 24 August, the COSIMA team saw a number of large dust grains from the comet on a target plate that had been pristine when examined one week before. A first examination of the plate indicates that the largest two grains are about 50 microns and 70 microns in width, comparable to the width of a human hair.

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In this image, several of 67P’s very different surface structures become visible. The left part of the images shows the comet’s “back”, while the right is the back of its “head”. The image was taken by OSIRIS, Rosetta’s scientific imaging system, on September 5th, 2014 from a distance of 62 kilometres. One pixel corresponds to 1.1 metres. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Scientists from the COSIMA team are now examining the image of the target plate in detail to determine the locations of the dust grains. Some will be selected for further analysis. The target plate will be moved to place each chosen grain under an ion gun which will then strip away the grain layer by layer. The material will then be analysed in a secondary ion mass spectrometer to determine its composition.

The results of these investigations are eagerly awaited since these are among the first dust grains to have been collected from beyond the Solar System’s snow line—the distance from the Sun at which ice grains can form.

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Left: An image of the target plate (measuring 1 cm by 1 cm) on which the grains were collected. Right: A section of the plate showing the state on 17 August (top) when no dust grains were visible and 24 August (bottom) when some large dust grains were detected. The length of the shadows is proportional to the height of the dust grains. The resolution of the image is 14 microns per pixel. Image credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

As both 67P and Rosetta travel closer to the Sun in the next months, the OSIRIS team will monitor the surface looking for changes. Even subtle transformations of the surface may help to explain how cometary activity created such a complex world.

Next weekend, on 13 and 14 September 2014, the maps will offer valuable insights as Rosetta's Lander Team and the Rosetta orbiter scientists gather in Toulouse to determine a primary and backup landing site from the earlier preselection of five candidates. 

Update: The Rosetta team today released a "selfie" portrait taken by the CIVA camera on Rosetta's lander Philae, which shows the spacecraft, its solar panels, and the comet itself in the background at a distance of about 50 km. It was taken on 7 September. You can see the image above.