The Rosetta orbiter, which has been tailing the comet 67P/Churyumov-Gerasimenko (67P/C-G) since August 2014, has sent back images of sinkholes on the solar system body - and they're completely unexpected.

The sinkholes on 67P/C-G may account for the activity that takes place along its surface, which include geysers that expel vaporized ice, dust, and poisonous gas; or rather, what lies beneath them. Inasmuch to this, they might bring scientists closer to understanding what makes it - and all comets - tick. 

"In the walls of these pits there are strange things, though we don't fully understand what they are," Jean-Baptiste Vincent, a planetary scientist at the Max Planck Institute, told Wired in an interview. "We see lots of fractures and features that look like pebbles - some people call them 'dinosaur eggs.' They look like the primordial pieces that make up the comets to begin with." 

Coined as "Europe's comet chaser," the Rosetta aircraft launched in 2004 after almost 10 years of planning. It's initial mission was to chase 67P/C-G and track the wax and wane of the comet's path, which is situated between the respective orbits of Earth and Mars, and how proximity to the sun changes the attributes of 67P/C-G's surface. Among other things, Rosetta is the first spacecraft in history to orbit a comet's nucleus.

On November 2014, Rosetta deployed the probe Philae, which landed on the comet's surface, also becoming the first in history to do so. After entering a seven-month period of hibernation, Philae became active again earlier this month.

Rosetta first noticed some unusual activity coming from a pit 650 feet in depth, and with a diameter more or less the same size. What quickly became clear was that the emitting subliminated comet matter (i.e., ice vaporizing into gas) was emanating from the sides of the pit, not the bottom of the cavity. 

Also found not far off from the sinkhole were flat-bottomed basins, too shallow to have been created by impact craters. As of now, their origin is yet unknown, though the current theory is that it's an inside job - terrestrial matter eaten away due to large subterranean hollows beneath the comet's exterior layer. Yet this is one of many feasible hypotheses.

"We don't know quite yet," continued Vincent, "We basically have the story with the eight blind men with the elephant and everyone thinks it's different. One of my jobs on this mission is to figure out how the eight pieces of information fit together."

With any luck, the following months of study, with help from the Rosetta, will continue to do just that.

Rosetta recently got the go-ahead for extended funding until September 2016 from the European Space Agency. The end date for the Rosetta mission was originally scheduled for December 2015.

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