NASA’s Hubble Detects First-Ever Spin Reversal of Tiny Comet
NASA’s Hubble Space Telescope has recorded the first confirmed reversal of a comet’s spin, a finding reported in a paper published Thursday in The Astronomical Journal. The observation concerns comet 41P/Tuttle‑Giacobini‑Kresák, a small Jupiter‑family body that returned to the inner solar system in 2017. Researchers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, analyzed Hubble imaging from December 2017 and combined it with earlier data from the Neil Gehrels Swift Observatory and the Discovery Channel Telescope at Lowell Observatory, Arizona, to document the phenomenon.
Comet 41P, likely sourced from the Kuiper Belt and later perturbed onto its current 5.4‑year orbit by Jupiter’s gravity, possesses a nucleus roughly 0.6 miles (about one kilometre) across, making it unusually susceptible to torque from outgassing. In March 2017 the comet’s rotation period measured between 46 and 60 hours; by May 2017 Swift data showed the spin had slowed to roughly three times that rate. Hubble images captured in December 2017 revealed a rapid increase to a 14‑hour period, indicating not only a halt but a reversal of the spin direction. The authors attribute the change to uneven jets of sublimating gas acting like small thrusters, a mechanism described by UCLA astronomer David Jewitt. Comparative analysis also notes that gas production during the 2017 perihelion was about ten times lower than during the 2001 passage, suggesting swift depletion or burial of near‑surface volatiles and a rapid evolution of the comet’s surface. Modeling of measured torques and mass‑loss rates indicates that continued acceleration could exceed the nucleus’s structural limits, potentially leading to fragmentation or disintegration.
The discovery underscores the value of long‑term archival data, as the Hubble observations were retrieved from the Mikulski Archive for Space Telescopes, a repository that stores more than three decades of imaging and spectroscopic data from Hubble and other missions. The project, operated jointly by NASA and the European Space Agency with mission support from Lockheed Martin Space and science operations conducted at the Space Telescope Science Institute in Baltimore, continues to enable new insights from historic datasets. The spin‑reversal event provides a rare, human‑scale view of cometary physical evolution, offering a benchmark for models of small‑body dynamics that are relevant to both scientific research and planetary‑defense considerations.
