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Comet may be developing sinkholes

July 2, 2015
Courtesy of the University of Maryland
and World Science staff

A com­et at the center of a Eu­ro­pe­an Space Agen­cy space­craft’s orbit has sev­er­al “sink­holes”—al­most per­fectly round pits, as wide and deep as a few foot­ball fields, as­tro­no­mers say.

These seem to arise through a pro­cess “very si­m­i­lar to the way sink­holes form here on Earth,” said Den­nis Bode­wits of the Uni­vers­ity of Mar­y­land, co-author of a re­port on the find­ings. 

The most active pit, known as Seth_01, on the surface of comet 67P/Chu­ryu­mov-Ge­ras­i­men­ko as photo­graphed by the Ro­setta craft. A new study suggests that this pit and others like it could be sink­holes. (Credit: Vincent et al., Nature Publishing Group)


Sink­holes form when ma­te­ri­al un­der­ground erodes, hol­low­ing out the ground so that the sur­face above even­tu­ally col­lapses. 

On com­et 67P/Chu­ry­u­mov-Ge­ras­i­men­ko, the study sug­gests, sink­holes form af­ter ices be­neath the sur­face va­por­ize.

The find­ings are one in­dica­t­ion that this com­et changes con­stantly as it ap­proaches the Sun, ac­cord­ing to the re­search­ers. 

The stu­dy, which ap­pears in the July 2 is­sue of the jour­nal Na­ture, sug­gests that far from sim­ple balls of ice and dust, com­ets have life cy­cles. 

From Earth sink­holes, Bode­wits said, “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.”

Sci­en­tists be­gan to won­der about the sur­pris­ingly deep pits al­most im­me­di­ately af­ter the space­craft, called Ro­set­ta, started cir­cling the com­et last Au­gust. “These strange, cir­cu­lar pits are just as deep as they are wide. Ro­set­ta can peer right in­to them,” said Bode­wits. Their widths range from tens, to sev­er­al hun­dred me­ters or yards.

Bode­wits and co-authors an­a­lyzed im­ages from a cam­era on Ro­set­ta called the Op­ti­cal, Spec­tro­scop­ic and In­fra­red Re­mote Im­ag­ing Sys­tem. 

They not­ed two dis­tinct types of pits: deep ones with steep sides and shal­lower ones that more closely re­sem­ble those seen on oth­er com­ets, such as 9P/Tem­pel 1 and 81P/Wild. The team al­so saw that jets of gas and dust streamed from the sides of first type, but not the sec­ond.

In­i­tial­ly, the sci­en­tists sus­pected some sorts of ex­plo­sions might be cre­at­ing the deeper pits. Ro­set­ta ob­served one such out­burst dur­ing its ap­proach to the com­et, on April 30, 2014. But it turned out that such ex­plo­sions weren’t nearly big enough to explain the holes.

The ex­plo­sion “could only ex­plain a hole a cou­ple of me­ters” or yards wide, Bode­wits said. “It seems that out­bursts aren’t driv­ing the pro­cess, but in­stead are one of the con­se­quences.”

The re­search­ers pro­pose that a source of heat be­neath the com­et’s sur­face causes ices, mainly wa­ter, car­bon mon­ox­ide and car­bon di­ox­ide, to sub­li­mate. The voids cre­at­ed by the loss of these ice chunks even­tu­ally grow large enough that their ceil­ings col­lapse.


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A comet being circled by a European Space Agency spacecraft has several “sinkholes”—almost perfectly round pits, as wide and deep as a few football fields, astronomers say. These seem to arise through a process “very similar to the way sinkholes form here on Earth,” said Dennis Bodewits of the University of Maryland, co-author of a report on the findings. Sinkholes occur when material underground erodes, hollowing out the ground so that the surface above eventually collapses. On comet 67P/Churyumov-Gerasimenko, the study suggests, sinkholes form after ices beneath the surface vaporize. The findings are one indication that this comet changes constantly as it approaches the Sun, according to the researchers. The study, which appears in the July 2 issue of the journal Nature, suggest that far from simple balls of ice and dust, comets have their own life cycles. From Earth sinkholes, Bodewits said, “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.” Scientists began to wonder about the surprisingly deep pits almost immediately after the spacecraft, called Rosetta, started circling the comet last August. “These strange, circular pits are just as deep as they are wide. Rosetta can peer right into them,” said Bodewits. Their widths range from tens, to several hundred meters or yards. Bodewits and co-authors analyzed images from a camera on Rosetta called the Optical, Spectroscopic and Infrared Remote Imaging System. They noted two distinct types of pits: deep ones with steep sides and shallower ones that more closely resemble those seen on other comets, such as 9P/Tempel 1 and 81P/Wild. The team also saw that jets of gas and dust streamed from the sides of first type, but not the second. Initially, the scientists suspected some sorts of explosions might be creating the deeper pits. Rosetta observed one such outburst during its approach to the comet, on April 30, 2014. But it turned out that such explosions weren’t nearly big enough. The explosion “could only explain a hole a couple of meters” or yards wide, Bodewits explained. “The pits we see are much larger. It seems that outbursts aren’t driving the process, but instead are one of the consequences.” The researchers propose that a source of heat beneath the comet’s surface causes ices, mainly primarily water, carbon monoxide and carbon dioxide, to sublimate. The voids created by the loss of these ice chunks eventually grow large enough that their ceilings collapse.