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If you were standing on the surface of Comet 41P/Tuttle-Giacobini-Kresák nine years ago as it neared the sun, you would have experienced each day on the comet getting drastically longer until its rotation stopped and it started going backward.

David Jewitt, an astronomer at UCLA, used images taken by the Hubble Space Telescope in December 2017 to study the comet. Like planets, moons and asteroids, comets spin naturally, and astronomers had already seen that 41P’s spin was slowing substantially, before Hubble’s observations revealed it was spinning in the opposite direction.

“We’ve seen changes in spin” on a comet before, said Jewitt, who published his findings on the website arXiv before publication in The Astronomical Journal. “But not this big and so quick.”

Images from NASA’s Swift telescope showed that when the comet was nearest the sun between March and May 2017, its rotation slowed to once every 46 hours. But Hubble showed it had quickened again to about every 14 hours. This made sense only if between May and December it had “slowed down to zero, and then kept going in the opposite direction,” Jewitt said.

“People have thought this should happen, but as far as I know this is the first observation to catch a comet doing that in the act,” said Jane Luu, an astronomer with the University of Oslo who was not involved in the study.

The finding is important because comets, particularly smaller ones, are less common in the solar system than astronomers would expect. One explanation might be that some like Comet 41P have jets that make them spin faster and faster until they are “blown to bits by their own spin,” Jewitt said.

“The evidence is that comets just don’t live that long,” he added. “There’s some other process that destroys the comets, and I think it’s rotation.”

This article originally appeared in .

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