Astronomers have detected Comet 41P/Tuttle-Giacobini-Kresák reversing its rotation direction, marking the first rapid such change observed in a celestial body. The 1-kilometer-wide comet slowed from a 20-hour spin in March 2017 to 46-60 hours two months later, then accelerated to about 14 hours by December. Researchers suggest outgassing from sublimating ice caused the reversal.
Comet 41P/Tuttle-Giacobini-Kresák orbits the sun every 5.4 years and approaches Earth periodically. It was observed during its 2017 inner solar system pass. David Jewitt at the University of California, Los Angeles, reanalyzed Hubble Space Telescope data from December 2017, revealing the comet's spin had reversed and sped up to one rotation every 14 hours or so after slowing dramatically earlier that year. Earlier observations in March 2017 showed a spin period of about 20 hours, which lengthened to 46 to 60 hours by May. The simplest explanation involves sunlight heating surface ice, causing it to sublimate into gas jets. If a jet fired opposite the original spin, it could slow the rotation to zero and then accelerate it in the reverse direction, according to researchers. “It is the first detected ‘fast’ change of the rotation direction for a celestial body,” said Dmitrii Vavilov at the University of Washington in Seattle. Such significant rotational shifts typically take decades or centuries in celestial bodies. Jewitt expects the nucleus to self-destruct soon due to excessive spin stress, potentially exposing ancient ice from the solar system's formation. “I expect this nucleus will very quickly self-destruct,” Jewitt said in a statement. John Noonan at Auburn University anticipates monitoring the comet during its next appearance in late 2027 or early 2028 to check for fracturing. Studying any fragments could provide insights into early solar system chemistry. The findings appear in The Astronomical Journal.
