The European Space Agency’s Rosetta probe has observed huge pits in the surface of Comet 67P.
Rosetta mission scientists say that the pits form thanks to a process similar to that responsible for the formation of sinkholes on Earth. As material under the surface of the comet vaporizes, the surface collapses into the holes, writes Jonathan Amos for the BBC.
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Sinkhole formation believed to follow similar process as on Earth
The collapse of these ceilings has resulted in cylindrical holes, some of which are over 100 meters deep and provide a window into the comet’s interior.
“They are almost as deep as they are wide,” said Jean-Baptiste Vincent, who works at the Max Planck Institute for Solar System Research in Germany. “The largest one is about 200m wide and 200m deep. It’s amazing because it gives us the possibility to look inside the comet for the first time,” he said.
A report on the observations has been published in this week’s edition of the journal Nature.
Sinkholes are often observed on Earth, particularly in areas of easily erodible rock like limestone. Sediments below the surface of the Earth are slowly eroded by acid rain, and when the weight of the earth above can no longer be supported, the ceiling collapses. It is thought that a similar process causes the pits on Comet 67P.
Comet could be shaped by sinkholes
So far the Rosetta probe has identified 18 pits which will be studied further, all of which are situated on the lit, northern-hemisphere of the 4-kilometer-wide comet.
One theory is that the heating of the comet as it approaches the Sun drives off buried volatiles, a process which causes cavities to form below its surface. Despite the low-gravity environment, it is thought that the rocky ceilings above collapse in on themselves as they cannot support their own weight.
Without the cover of dust and rock, the walls of the newly formed pits are exposed to direct sunlight, which causes the ice inside them to vaporize. Rosetta has previously sent back images in which gas and dust can be seen flying off the walls.
It is thought that the sinkholes eventually become shallower basins, which in turn merge with other, neighboring basins, in a process which scientists think gives the comet its distinctive shape.
Rosetta entering critical observation period
Scientists interested in the composition of 67P have previously been excited by lumps and bumps found to exist inside the pits, which have been likened to “goosebumps.”
“All the goosebumps we have observed on the comet – they are inside these pits,” said Dr Vincent.
Comet 67P and the Rosetta probe are hurtling towards the Sun, and will reach their closest point to our star next month. After reaching perihelion, as that point is known, the comet will then slingshot back out into the outer reaches of the Solar System.
Perihelion marks the point where just 186 million kilometers separates Comet 67P from the Sun, and it is predicted that activity will increase on the comet’s surface due to higher temperatures.
Not only is the Rosetta probe observing the comet from above its surface, it is maintaining contact with the Philae lander which successfully landed on the comet in November 2014. Philae was put into hibernation for a time, but was recently brought back to life. ESA mission control is working to ensure stable communications with the vehicle before it starts observing activity on the surface of the comet during the impending perihelion.