Rosetta: Spacecraft Reveals Sinkholes On Comet’s Surface

Comet 67P/Churyumov-Gerasimenko, the comet being orbited by the European Space Agency’s Rosetta spacecraft, has puzzled scientists with deep, almost perfectly circular pits on the it’s surface, since the probe reached the comet in August 2014.

A new study analyzing close-up images taken by Rosetta suggests that these pits are sinkholes, formed when ice beneath the comet’s surface turn directly to gas, much like sinkholes here on Earth.

Co-author Dennis Bodewits, assistant research scientist in astronomy at the University of Maryland, says:

“These strange, circular pits are just as deep as they are wide. Rosetta can peer right into them. The pits are large, ranging from tens of meters in diameter up to several hundred meters across.”

They range in size from tens of meters in diameter up to several hundred meters across.

“We propose that they are sinkholes, formed by a surface collapse process very similar to the way sinkholes form here on Earth,” Bodewits added. “So we already have a library of information to help us understand how this process works, which allows us to use these pits to study what lies under the comet’s surface.”

The images were generated by Rosetta’s Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) narrow angle camera, specially designed to image the surface of the comet’s nucleus.

The research team saw two distinct types of pits.

The first are deep ones with steep sides. There are also shallower pits more closely resembling ones seen on other comets, such as 9P/Tempel 1 and 81P/Wild.

The team also noted that jets of gas and dust streamed from the sides of the deep, steep-sided pits. This phenomenon they did not see in the shallower pits.

Researchers have proposed a model for the formation of the sinkholes.

A source of heat beneath the comet’s surface causes ices, mostly of water, carbon monoxide and carbon dioxide, to sublimate. The empty spaces created by the loss of the ice chunks sooner of later grow big enough that their ceilings collapse under their own weight, giving rise to the deep, steep-sided circular pits seen on the surface of comet 67P/Churyumov-Gerasimenko.

On June 23, 2015, the European Space Agency extended the Rosetta mission by nine months, from the planned end date of December 2015 to September 2016. The spacecraft will now be able to track comet 67P/Churyumov-Gerasimenko for a much longer time period as it moves away from the sun.

Reference:

Jean-Baptiste Vincent, et al.
Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse
Nature 523, 63–66 doi:10.1038/nature14564

Photo: Close-up image showing the most active pit, known as Seth_01, observed on the surface of comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft. Credit: Vincent et al., Nature Publishing Group