Since its arrival at Comet 67P/Churyumov-Gerasimenko (Comet 67P/C-G), the Rosetta spacecraft of the European Space Agency has been seeing “dramatic and rapid changes” on the surface of the active comet, which moves closer to the sun in its orbit.

As reported in a study published in Astronomy and Astrophysics, Rosetta scientists have been witnessing these surface changes on Imhotep, located on the largest lobe of the cometary nucleus and featuring smooth terrains covered with fine-grain material and huge boulders.

Olivier Groussin, lead study author and astronomer from the Laboratoire d'Astrophysique de Marseille, France, said they have been monitoring the region closely starting in August 2014.

In June this year after a series of captures from the Rosetta’s Osiris camera (Optical, Spectroscopic, and Infrared Remote Imaging System), a growing feature emerged and was joined by a similar second round feature, both growing in size. By July 2, their diameters had been established at around 220 meters and 140 meters.

A third feature showed and the three shortly merged into a large region, with another two appearing. Olivier added that the features' rims are expanding by a couple of tens of centimeters per hour, highlighting “the complexity of the physical processes involved.”

What could be causing these changes? The surface material could be weak, leading to rapid erosion. Also likely involved are the crystallization of amorphous ice as well as the destabilization of “clathrates,” potentially liberating energy and driving the faster-than-usual expansion of the features.

The process, according to the researchers, involves increased gas outflow rates, including H2O, CO2, or CO. Incited by Comet 67P being hit by sunlight, the sublimation of volatiles must also be involved.

Rosetta was the first spacecraft to closely watch a comet during perihelion, particularly at 02:03 GMT when the comet passed within 186 million miles of the sun. Comets are most active during their closest brush with the sun – jets of gas and dust erupt from their surfaces.

Perihelion, on the other hand, took place nine months after the deployment of the Philae lander and landing on the surface of the comet.

Philae resumed its actions on the surface last June, finding the surface “littered with coarse debris” and “a suite of 16 organic compounds” made up of various carbon and nitrogen-rich compounds.

Rosetta is poised to make more observations on Comet 67P as the active comet’s activity remains high in the next few weeks. This science mission has been extended through September 2016.

Photo: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

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