Using NASA’s Hubble Space Telescope, astronomers have found the first-ever evidence that a comet reversed its direction of rotation. The small space object, comet 41P/Tuttle-Giacobini-Kresák, likely came from the Kuiper Belt and was catapulted into its current trajectory by Jupiter’s gravity.

First-Ever Comet Spin Reversal

Scientists first noticed that comet 41P was experiencing a dramatic slowdown after its 2017 passage around the sun, and a new analysis shows an even more drastic change. Hubble images from December 2017 detected the comet spinning faster again, leading researchers to believe that the comet continued slowing until it was forced to spin in the near-opposite direction by outgassing jets on its surface.

Hubble also measured the comet at around 0.6 miles across, which is approximately three times the height of the Eiffel Tower. As this is a particularly small size for a comet, it’s easier for the object to twist.

“Jets of gas streaming off the surface can act like small thrusters,” said paper author David Jewitt of the University of California at Los Angeles. “If those jets are unevenly distributed, they can dramatically change how a comet, especially a small one, rotates.”

“It’s like pushing a merry-go-round,” Jewitt added. “If it’s turning in one direction, and then you push against that, you can slow it and reverse it.”

Comet 41P has likely occupied its present orbit for approximately 1,500 years. The study also shows that the comet’s overall activity has significantly declined since earlier cycles, suggesting the comet’s surface is evolving quickly, as comet structure changes typically occur over centuries.

This evolution could potentially involve near-surface volatile materials that became covered or depleted by dust layers. Researchers speculate that, based on the measured torques and mass loss rates, continued rotational changes could eventually make the comet structurally unstable.

The science paper detailing this finding was published in The Astronomical Journal.