comet too hot to be covered in ice ESA
1 August 2014
ESA’s Rosetta spacecraft has made its first temperature measurements of its target comet, finding that it is too hot to be covered in ice and must instead have a dark, dusty crust.
The observations of comet 67P/Churyumov–Gerasimenko were made by Rosetta’s visible, infrared and thermal imaging spectrometer, VIRTIS, between 13 and 21 July, when Rosetta closed in from 14 000 km to the comet to just over 5000 km.
At these distances, the comet covered only a few pixels in the field of view and so it was not possible to determine the temperatures of individual features. But, using the sensor to collect infrared light emitted by the whole comet, scientists determined that its average surface temperature is about –70ºC.
The comet was roughly 555 million kilometres from the Sun at the time – more than three times further away than Earth, meaning that sunlight is only about a tenth as bright.
Although –70ºC may seem rather cold, importantly, it is some 20–30ºC warmer than predicted for a comet at that distance covered exclusively in ice.
“This result is very interesting, since it gives us the first clues on the composition and physical properties of the comet’s surface,” says VIRTIS principal investigator Fabrizio Capaccioni from INAF-IAPS, Rome, Italy.
http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_takes_comet_s_temperature