The latest temperature scans of Comet Churymov-Gerasimenko should help mission planners choose a site that's neither too hot nor too cold for the Philae lander.

Above: An orthographic projection of the comet's surface centred on the 0° meridian (left) and the 180° meridian (right), showing the temperature for local time between 12h and 14h. The measurements were obtained in July and August 2014 when the comet was between 3.6AU and 3.45AU from the Sun, and the spacecraft was closing in from 14,000km to less than 100 km from the comet nucleus. The locations of the five candidate landing sites for the Philae lander are indicated. Credit: ESA/Rosetta/VIRTIS/INAF-IAPS/OBS DE PARIS-LESIA/DLR

Following the Rosetta spacecraft's arrival at the Comet in early August, the onboard VIRTIS imaging spectrometer has been busy at work scanning the surface. Results revealed a surface with surprising variability in temperature, including regions as "high" as 230 K (-46 degrees F). The average surface temperature is about 205 K (-90 degrees F).

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Measurements of the surface temperature can provide clues to the composition and physical properties of a comet. These new VIRTIS measurements have allowed the team to rule out some models of the comet surface and to favour a comet surface composed of a porous and highly thermally insulating dusty crust that is depleted of water ice. As they reported today, this is also consistent with the VIRTIS global measurements of thermal inertia – a measure of a body's resistance to changes in temperature – that is compatible with the value for high porosity dusty materials.

The relatively high spatial resolution of the VIRTIS measurements have also allowed the team to investigate thermal shocks that happen when a region enters or exits from shadow. This is of interest because thermal shocks can give rise to stresses in the surface, which can lead to micro-cracks and eventually result in fractures in the surface.

The team have also been poring over the spectra to search for hints about the chemical makeup of the surface of comet 67P/C-G. Among the preliminary results reported today was no evidence of water ice on a global scale, confirming that the outer surface is generally dehydrated.


So a picture is slowly starting to emerge about Comet 67P/C-G — one that paints it as a dark, dry, and dusty comet, but one with a rich and complex chemistry.

In related news, scientists working on images of the comet have divided the comet's surface into a number of different regions, revealing a unique, multifaceted world.


Several morphologically different regions are indicated in this map, which is oriented with the comet's 'body' in the foreground and the 'head' in the background. [ Credit: ESA/Rosetta/MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA ]

Here's a beautiful detailed photograph of the comet.


The image was taken on September 5 from a distance of 62 kilometers. The left part of the image shows a side view of the comet's 'body', while the right is the back of its 'head'. One pixel corresponds to 1.1 metres. [ Credit: ESA/Rosetta/MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA ]