Sinkholes Offer Glimpse into Comet’s Heart

A new study shows that mysterious, steep-sided pits-one up to 600 feet wide and 600 feet deep-discovered by the Rosetta spacecraft on the surface of comet 67P/Churyumov-Gerasimenko are probably sinkholes caused by weaknesses in the ground beneath the comet’s surface.

A report on the observations has been published in this week’s edition of the journal Nature.

Shortly after landing on the comet previous year, scientists noticed several deep and nearly perfectly circular pits on the surface. Officials suspect these kinds of sinkhole formed in ways not unlike the way they do down here, on Earth.

Similar sinkholes occur on Earth when subsurface erosion removes large amounts of material beneath the surface, creating a cavern. More importantly, 67P’s sinkholes are giving scientists a chance to peer deep into the comet’s belly, which may include material that existed during the very formation of our solar system.

Images of the comet taken by the European Space Agency’s Rosetta probe show the object’s surface is spotted with flat-bottomed pits that are emitting jets of gas. However, researchers couldn’t pay much attention to them because of being too engrossed in mapping the comet’s craggy surface.

Scientists hope the newly-awakened Philae lander will be able to conduct more detailed analysis of the comet’s internal structure, and Rosetta is slated to continue observing the comet until September, 2016. Since the pits are active, they change with time, says Vincent.

After travelling some six billion kilometres, the spacecraft caught its first glimpse of the comet in March 2014, from a distance of about five million km – when it was just a small dot in the sky. These fractured regions signify that there are volatiles that are trapped under its surface where they are warmed and eventually escape into deep space.

“Clusters of active pits and collapsed structures are signatures of former cavities underneath, and reflect the thermal history of the nucleus”.

Plenty of questions remain, including the exact nature of the comet core’s heat source, and whether 67P will become more worm-eaten as it treads closer to the sun (the comet reaches perihelion, or its closest point to the sun, on August 13th).

Over time, the sinkholes will likely open out into shallower basins, and these basins will probably also merge. It is thought that a similar process causes the pits on Comet 67P.

Researchers are eager to observe the evolution of the active pits and could even see the formation of a new one, says ESA project scientist Matt Taylor in the statement.

“I think they are sinkholes, but I don’t know that for certain”, Weissman, who was not involved in the research, told Discovery News.

Or it could be that the ice manages to melt itself away by transforming from amorphous ice made up of irregularly packed molecules to crystallised ice, a process that would release heat which could be sufficient to cause evaporation. Indeed, Rosetta astronomers have observed gas jets streaming out of some of the deeper holes, supporting the notion that the comet’s architecture is actively evolving.