Dark jets of dust on the 67P/ Churyumov-Gerasimenko

Thanks to high-resolution images of the imaging instrument of OSIRIS, jets of dark dust on the surface of 67P could be observed with unprecedented detail, a clear sign of increased activity in the nucleus of the comet.
When night falls on the comet Rosetta, the 67P / Churyumov-Gerasimenko, its body strangely shaped remains very active. This is what it is observed in the recent images of the region called Ma’at, located on the “head” of the comet, captured by the instrument OSIRIS, the imaging system aboard the Rosetta space probe that has contributed significantly with the University of Padua the CISAS. These images were collected half an hour after sunset on the region and show jets of dust that are dispersed in space. Researchers from the OSIRIS team believe that behind this phenomenon there is the gradual heating of the comet.



“Only recently have we begun to see the jets of dust that persist even after sunset,” says the Principal Investigator of OSIRIS Holger Sierks of the Max Planck Institute for Solar System Research (MPS) in Germany. In recent months the activity of the comet was placed in the areas illuminated by the sun. Immediately after sunset these jets are lowered and not awakened unless the next dawn. An exception is represented by the image in March 12, 2015 that shows the beginning of a powder jet from an area close to that in which begins the dawn.
According to scientists of the OSIRIS team, the presence of jets even after sunset is a new sign of growing of the comet. “Currently 67P is approaching the perihelion, which is scheduled for mid-August,” said Sierks. At the time when the picture was taken, the comet and the Sun were just 270 million kilometers away. “Solar radiation is becoming more intense, and therefore the illuminated surface is increasing its temperature,” added Sierks.



Early analysis suggests that the comet could store this heat for a longer period of time in its surface layers. “As the dust covering the surface of the comet cools quickly after sundown, the deeper layers retain heat for a longer period of time,” says Shi Xian, scientist at the MPS OSIRIS team that examined the jets on the surface of the comet. Scientists suspect that these layers are actually a supply of frozen gas that fuels the activity of the comet.
Even cometary missions of the past, as the Stardust comet 81P / Wild 2 and Deep Impact on Comet 9P / Tempel 1, had observed the presence of jets along the surface at night. “But only thanks to high-resolution images of OSIRIS we can study this phenomenon in detail,” concluded Sierks.

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