Comets have sinkholes much like those on Earth, a new finding from the Rosetta spacecraft reveals. This finding overturns a long-held idea in astronomy about the icy bodies.

Rosetta is currently orbiting comet 67P/Churyumov-Gerasimenko (67/P), where the observatory has spent more than a year carefully examining the surface of the frozen mountain in space.

Comets develop their distinctive tails as material is cast off the icy body and driven backward by pressure from the sun. Astronomers used to believe this emission of gas and dust occurred nearly evenly over the surfaces of these bodies. These new findings, made utilizing the Rosetta orbiter, show the material is thrown from the comet, predominantly from sinkholes.

Recorded by the Osiris camera onboard the craft, this is the first time that such sinkholes have been seen pockmarking the surface of a comet. Astronomers have recorded 18 of these features so far in the northern hemisphere of the comet, many of which appear to be casting out material to space.

"We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space," said Jean-Baptiste Vincent of the Max Planck Institute for Solar System Research.

Each of these sinkholes measures between a few dozen and several hundred feet in diameter and are up to 650 feet deep. They likely form when material covering subsurface cavities collapses, creating a cave-like structure. This allows solid material on the inside of the feature to sublimate, transforming from solid to a gaseous state. This process continues the erosion, allowing the sinkhole to grow over time.

"Although we think the collapse that produces a pit is sudden, the cavity in the porous subsurface could have growing (sic) over much longer timescales," Sebastien Besse from the European Space Agency (ESA) European Space Research and Technology Centre (Estec) told the press.

Currently, researchers have three theories on what could cause these sinkholes to form. The first is that they were there from the time the body was formed. The second is that material underneath the surface sublimated to space through heating from the sun. The third possibility is that the sinkholes were from physical reactions between water and other materials in the body.

Astronomers believe study of these cometary sinkholes could help them learn more about the dynamic processes that take place beneath the surfaces of these bodies.

Analysis of the sinkholes in Comet 67/P and processes leading to the emission of material from these newly discovered features was profiled in the journal Nature.

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