Astronomers in 1985 spotted a peculiar comet that seemed to have a huge blob of dust travelling with it through space, and now we have finally figured out what it is. Understanding unusual objects like this could help us learn about how comets evolve and eventually fall apart.
at the Technical University of Braunschweig in Germany and her colleagues examined the comet, called Comet 108P/Ciffreo, using the Nordic Optical Telescope in Spain and the Hubble Space Telescope to get a closer look at its strange companion. They found that the body of the comet itself was about 1 kilometre across, but the dust clump moving alongside it measured close to 5000 kilometres across. 鈥淲e鈥檝e never seen this kind of blob in other comets,鈥� says Kim.
When the blob was first discovered, researchers thought it was most likely a separate object, perhaps a part of the comet that had fragmented off. Later, other scientists suggested it might have been particles launched off the comet when sunlight heated ice on its surface, turning the ice into a gas in a process called sublimation. Kim and her team used their fresh observations to construct a series of simulations in an effort to tell which explanation fit.
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The blob reappeared every time astronomers spotted the comet coming close to the sun, which made fragmentation an unlikely explanation 鈥� it wouldn鈥檛 make sense for the comet to start breaking apart in exactly the same way at the same point in its orbit over and over again. Instead, the blob is probably made of dust from the comet itself.
However, the location of the blob between the comet and the sun and the fact that it is a single object instead of being spread out indicate that the dust probably came off the comet in a jet. The researchers suggest that this could be because the ice that is lofting the dust off the comet is located at the bottom of a pit, so when sunlight streams into the pit, the dust and gas is propelled up in a single jet. Then, as it moves from the comet towards the sun, the jet turns back on itself because of the radiation pressure from the sunlight, forming a blob that stays near the comet.
Kim and her team plan to find and model more unusual comets in the coming years, and new telescopes such as the Vera C. Rubin Observatory in Chile should be able to spot many more. 鈥淭here should be more strange and peculiar comets, and observation and modelling them helps us explain the life cycles of all comets,鈥� says Kim.
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