Comet 41P appears to have reversed its spin

Hubble image analysis and lightcurve measurements indicate that Comet 41P/Tuttle-Giacobini-Kresák's small nucleus likely reversed its rotation between April and December 2017 after a dramatic slowdown was observed earlier that year.

Comet 41P/Tuttle-Giacobini-Kresák is a small, active comet that showed an unusually large change in rotation in 2017. Observers recorded a dramatic slowdown during its April 2017 Earth flyby. A recent analysis of Hubble Space Telescope images from December 2017 by David Jewitt indicates the nucleus likely reversed its spin direction between April and December 2017. Jewitt also estimated the nucleus radius at roughly 0.3 miles (0.5 kilometers). Key findings: - Hubble image analysis and lightcurve measurements suggest the comet's rotation reversed sometime after its closest approach to the Sun in April 2017 and before December 2017. - Independent observations earlier in 2017 reported the rotation period slowing from about one turn every 20 hours in March to one every 46 hours by May. - Jewitt estimated the nucleus radius at roughly 0.3 miles (0.5 kilometers) based on brightness and non-gravitational acceleration. - The change in 41P's spin was larger and faster than previously recorded comet slowdowns, such as 103P/Hartley 2's smaller change over a longer interval. - Jewitt has suggested that outgassing torque on sub-kilometer comets can rapidly alter rotation and may contribute to their short lifetimes. Summary: The observations add evidence that uneven outgassing can apply strong torque to small comet nuclei, sometimes reversing rotation within months. Jewitt has proposed that such rapid rotational changes could be a factor in the loss of small comets. Astronomers plan another opportunity to observe 41P when it returns in 2028.