Comet 41P Dramatically Changes Rotation Speed
Comet Giacobini-Zinner dramatically changed its rotation over 60 days, slowing from once every 20 hours to once every 53 hours and possibly reversing direction. This transformation is attributed to non-gravitational perturbations from outgassing material acting like a rocket engine as the comet approaches the sun.
Comet 41P/Tuttle-Giacobini-Kresák is a Jupiter-family comet with a looping 5.4-year orbit. It was first discovered by Horace Tuttle in 1858, then independently re-discovered by Michel Giacobini in 1907 and again by Ľubor Kresák in 1951. The dramatic 2017 spin-down was documented by multiple teams. A group led by Dennis Bodewits of Auburn University used NASA's Swift telescope to clock the initial slowdown, while David Jewitt of UCLA later used the Hubble Space Telescope to confirm the final state of the comet's rotation. After the initial slowdown from a 20-hour to a 53-hour rotation period, the comet passed too close to the sun to be observed. When it reappeared in December 2017, observations from Hubble revealed its rotation had actually sped up to just 14.4 hours, providing strong evidence its spin had reversed direction entirely. This change was unprecedented in both its scale and speed. For comparison, the previous record for a rotational slowdown was held by comet 103P/Hartley 2, which altered its spin from 17 to 19 hours over a period of 90 days. This comet has a history of unpredictable behavior. During its 1973 pass, it experienced a massive outburst that caused it to brighten by 10 magnitudes, making it briefly visible to the naked eye. With a nucleus less than a mile across, some astronomers theorize that the powerful jets causing these rotational shifts could eventually spin the comet apart. Its next close approach to the sun will be in early 2028.
