The Hubble Space Telescope made an astonishing find: it observed a spinning comet that actually changed its rotation direction. This marks a first in our understanding of cometary behavior.
The comet in question is 41P/Tuttle–Giacobini–Kresák, part of a group known as Jupiter-family comets. These short-period comets orbit the sun every 5.4 years and originate from the Kuiper Belt. It last made a close approach to the sun in September 2022, with its previous encounter occurring in 2017 when the Hubble, along with other major telescopes, captured data on it.
David Jewitt, a planetary scientist at UCLA, discovered intriguing patterns when he analyzed the Hubble data, which had been archived since its 2017 observations. In May 2017, the comet was rotating slowly, taking about 46 to 60 hours to spin once. By December 2017, however, it sped up dramatically to just about 14 hours per rotation. What caused this sudden change?
Jewitt suggests that outgassing is the answer. During perihelion—when the comet gets close to the sun—the heat causes volatile gases beneath the surface to expand and escape. This process creates jets that can act like thrusters. “If those jets are unevenly distributed, they can dramatically change how a comet rotates,” he explained.
Interestingly, Hubble’s observations show that this small comet, with a nucleus just 0.6 miles (1 kilometer) across, is particularly vulnerable to such forces. The jets produced by the outgassing slowed its original spin before reversing its direction entirely. Jewitt likens this to pushing a merry-go-round in the opposite direction. The comet’s instability could lead to its eventual destruction if it keeps spinning faster.
Historically, comets have been known for their unpredictability, but this particular behavior is rare. In 2001, Hubble noted that 41P had a lot more activity at perihelion than it does now, indicating possible depletion of its volatile ices. Research suggests that the comet has likely been on its current path for about 1,500 years, and these repeated close encounters could exhaust its resources.
Jewitt remains concerned that if the changes continue, the rotating forces could tear the comet apart. “I expect this nucleus will very quickly self-destruct,” he stated. This finding emphasizes the dynamic nature of celestial bodies and raises questions about their long-term stability.
Recent data further supports Jewitt’s concerns. A study published in *The Astronomical Journal* on March 26 discusses the increasing instability in small comets. Understanding these changes not only enhances our knowledge of comets but also sheds light on broader patterns in cosmic evolution.
For more information on this groundbreaking discovery, check out the full study in *The Astronomical Journal* here.
