The 67P / Churyumov-Gerasimenko comet is too hot to be covered with ice and must have a dark, dusty surface instead. Astronomers conclude that now that Rosetta has measured the temperature of the comet for the first time.
The average surface temperature of the comet appears to be -70 degrees Celsius. Rosetta measured that temperature between 13 and 21 July, when the comet was still 555 million kilometers away from the sun. The distance between the comet and the sun was about three times greater than between the sun and the earth.
A temperature of -70 degrees seems low. But it is about 20 to 30 degrees Celsius warmer than researchers had expected for a comet covered in ice at this distance from the sun. "This result is very interesting because it gives us a first indication of the composition and physical properties of the surface of the comet," says researcher Fabrizio Capaccioni.
We already knew that the 67P / Churyumov-Gerasimenko comet reflected relatively little light. That already indicated that the comet could in any case not be completely covered with 'clean' ice (or very light ice that reflects a lot of light). The new measurements provide researchers with direct evidence that most of the surface is not covered with ice. Instead it would be quite dark. The surface may therefore be covered with dust instead of ice.
Little ice cream?
That does not mean that there is no ice on the comet anywhere. It is quite possible that some parts of the comet are covered with relatively clean ice. More clarity about this will come soon. Rosetta is then able to measure the temperature of individual surface structures.
In addition, Rosetta will study how the surface temperatures respond to the fact that the comet is getting closer to the sun. In this way we also receive more information about the density and porosity of the material just below the surface of 67P / Churyumov-Gerasimenko. That data can be used to find a place to put down lander Philae.
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