Comet 41P Reverses Spin in Rare Solar System Event, Astronomers Report
Astronomers have documented a rare and unprecedented event in the solar system, where a comet dramatically slowed its rotation and then began spinning in the opposite direction. This unusual behavior was observed in Comet 41P/Tuttle-Giacobini-Kresák, a small icy body approximately 0.6 miles across, as it approached the sun in 2017.
Hubble Telescope Captures Unprecedented Changes
David Jewitt, an astronomer at the University of California, Los Angeles, analyzed images taken by the Hubble Space Telescope to study this phenomenon. "We've seen changes in spin on a comet before," Jewitt stated, "but not this big and so quick." Like planets, moons, and asteroids, comets naturally spin, but the reversal observed in 41P marks a significant first in astronomical records.
Comets are chunks of rock and ice that originate in the outer solar system, remnants from the formation of planets. Occasionally, they are nudged into the inner solar system and swing past the sun. As they heat up, their ice sublimates into gas, forming visible tails. Often, comets are shrouded in a dense cloud of dust and gas, known as a coma, surrounding the solid nucleus.
Jets and Spin Alterations Explained
Some comets experience stronger events where material shoots out from the surface like a rocket. "We don't really understand that," said Dennis Bodewits, an astronomer at Auburn University. However, the force of these jets can be sufficient to alter a comet's spin—a process that occurred on 41P in an extreme form.
As 41P neared the sun in 2017, Bodewits and his team utilized NASA's Swift telescope to monitor changes in its brightness. Between March and May, the comet's rotation slowed from 20 hours to 46 hours per spin. Observations were halted after May because the comet was too close to the sun to be seen.
Reversal and Future Observations
When the comet reappeared in December 2017, Hubble revealed that its spin had quickened to about 14 hours. "Slowed down to zero, and then kept going in the opposite direction," Jewitt explained. Jane Luu of the University of Oslo added, "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."
Jewitt suggested that such jets may explain why smaller comets are rare. "There's some other process that destroys the comets, and I think it's rotation," he said. Comet 41P is expected to swing past the sun again in early 2028, and astronomers anticipate that new telescopes, such as the Vera C. Rubin Observatory, will reveal more comets undergoing chaotic changes.
