Cape Town - It’s a snowball, for sure, but with a shape like that, it’s not the kind that would feature in any kind of friendly snowball fight.

This is Comet 67P/Churyumov-Gerasimenko – 67P for short – that is being rapidly approached by the European Space Agency’s Rosetta probe. And as the days are being ticked off for the actual rendezvous next month, the comet’s core is coming into sharper focus.

Late last week, the agency released a new set of images and a striking three-dimensional model of 67P’s nucleus, showing how it was rotating and delineating its odd “bi-lobate” form – a smaller head connected to a larger body by a “neck”.

The 3D model of the nucleus was created from a recent set of images taken by the OSIRIS imaging system aboard the spacecraft that is scheduled to perform several historic space exploration firsts: orbiting a comet, analysing the comet as it is drawn into a fiery encounter with the sun and – hopefully – depositing a lander, or probe, on to the comet’s surface some time in November.

It will study the comet at close range “as it transforms from a quiet nugget of ice and rock, frozen solid by years spent in deep space, to a sun-warmed dynamo spewing jets of gas and dust into a magnificently evolving tail”, says Dr Tony Phillips, production editor of Nasa Science News.

Rosetta was launched on its 11-year journey by an Ariane 5 rocket from Kourou in French Guiana in March 2004 and entered deep space hibernation mode in June 2011. Then, with its destination in sight, it was “woken” on January 20 and its cameras turned on. The resolution of the latest images taken on July 20 is 100m per pixel, Phillips explains, and the neck of the comet that is about 3.5km by 4km in size is proving to be especially intriguing to investigators.

Principal investigator Holger Sierks from the Max Planck Institute for Solar System Research in Germany, says: “The only thing we know for sure at this point is that this neck region appears brighter compared to the head and body of the nucleus.”

This collar-like appearance could be caused by differences in material or grain size, or could be a topographical effect – “no one knows”, says Phillips.

One explanation for the high reflectivity of the neck could be a different surface composition, he suggests.

In coming weeks, the OSIRIS team hopes to analyse the spectral data of this region obtained with the help of the imaging system’s filters. These can select several wavelength regions from the reflected light, allowing scientists to identify the fingerprints of certain materials.

There have been previous comet fly-bys to collect data, but Rosetta will be the first to track a comet at close range as the comet’s orbit reaches its nearest point to the Sun, in August next year.

The spacecraft is due to finally shut down at the end of next year.


* On the web: http://www. for a video clip of the rotating comet.

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John Yeld, Cape Argus