Mysterious pits on this comet are actually enormous sinkholes


Scientists just discovered something amazing: sinkholes on a comet.

These are the first sinkholes ever detected on a comet, and some are so deep, you could fit the entire Washington Monument inside of one.

Not only that, they're likely the driving force behind giant jets of gas and dust - shown in the image to the right - the comet is spitting into space.


The sinkholes were recently discovered on 67P/Churyumov-Gerasimenko by a team of researchers at the University of Maryland who published their results in the July 2 issue of the journal Nature.

The team analyzed data collected by the Rosetta spacecraft, which began orbiting comet 67P/Churyumov-Gerasimenko in August 2014. Since then, Rosetta has captured the most detailed images of a comet in history. When scientists first looked at some of these photos, they were mystified by the hundreds of pits, like the one in the image below, dotting the desolate, lumpy surface.

Rosetta_image_comet_sinkhole with annotations

Vincent et al., Nature Publishing Group

These pits, of which there are approximately 380 across the entire comet, are now thought to be giant sink holes. Here's a closer shot of the same sinkhole.


Comets are basically dusty snowballs in space that orbit the sun. As they travel closer to the sun, they heat up and the ice underneath their surface will, in the vacuum of space, turn directly into a gas through a process called sublimation.

When this happens, the dust and rock on top of the ice no longer has anything holding it up, and it begins to collapse. This collapse generates giant sinkholes ranging from tens to hundreds of feet in diameter, the team reports.

"The sinkholes on 67P are very large, two football fields next to each other and deeper than the Washington monument," Dennis Bodewits, one of the authors of the study and an assistant research scientist of astronomy at the University of Maryland, told Business Insider in an email.


Moreover, once the sinkhole forms it exposes additional ice along the sides of the hole, which are what produce the brilliant jets the comet emits, like the ones below:

comet 67p 14 march 14 2015 (1)


Comet 67P/Churyumov-Gerasimenko captured by the Rosetta spacecraft March 14, 2015.

Until now, scientists thought the jets formed from thawing frozen gas on the surface, but it now seems that the story is more involved. The comet is about 4 billion miles from Earth, making it difficult to study these sink holes close up, but luckily they have a much closer analog: sinkholes on Earth, which form much the same way:

"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," Bodewits said in a press release.


The European Space Association, which is in charge of the mission, originally thought the pits were caused by explosive outbursts, causing dust jets to spew out of the comet.

But, the size of the pits was too large to be explained by the explosive events alone, they concluded. Now, scientists will need to figure out where the sinkholes factor into the lifecycle of a comet. Here's a graphic by the team showing how these sinkholes form and produce the comet's jets:


ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; graphic from J-B Vincent et al (2015)

In light of this discovery, you might wonder about the Philae lander that touched down on the comet last November - making history by becoming the first probe to ever land on a comet. Luckily, Bodewits says Philae is in no danger.


"While that does dwarf Philae (Rosetta's desk-sized lander), I am not concerned that it [will] disappear in a sink hole," Bodewits said.

That's because, he said, the sinkholes are clustered on specific parts of the comet, and none are near where Philae ended up near the head of the comet. That's good news, since Philae recently started sending back signals to Earth, which will teach us even more about the comet from the surface.

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