A comet that is only a kilometer wide—roughly three times the height of the Eiffel Tower, give or take—is doing something that, until recently, no one had ever seen a comet do. It is located somewhere beyond Mars. It decelerated. almost came to a halt. Then it started spinning in the opposite direction, propelled by its own escaping gases. Almost by accident, the entire sequence was recorded over the course of less than a year’s worth of Hubble Space Telescope observations. The data was clearly described by the researchers who analyzed it, but the paper’s language carries a hint of genuine surprise. This was not intended to occur. Alternatively put, it was theoretically feasible, but no one had ever witnessed it.
For about 1,500 years, Comet 41P/Tuttle-Giacobini-Kresák has been orbiting the Sun every 5.4 years. Jupiter’s gravity pushed it into its current orbit long ago. It’s a tiny, erratic object, and it turns out to be very important. The comet’s surface frozen gases sublimated when it passed near the Sun in early 2017, releasing jets of material into space in a manner similar to how a punctured aerosol can release pressure.
| Key Information: Comet 41P/Tuttle-Giacobini-Kresák | Details |
|---|---|
| Official Designation | Comet 41P/Tuttle-Giacobini-Kresák |
| Origin | Kuiper Belt — redirected by Jupiter’s gravity |
| Orbital Period | Every 5.4 years around the Sun |
| Nucleus Size | ~0.6 miles (approx. 1 kilometer) across — roughly 3x the height of the Eiffel Tower |
| Rotation Rate (March 2017) | Approximately 20 hours per full rotation |
| Rotation Rate (May 2017) | 46 to 60 hours — slowed by a factor of 3 |
| Rotation Rate (December 2017) | ~14 hours — reversed direction entirely |
| Cause of Spin Reversal | Outgassing jets acting as natural thrusters against the original spin direction |
| Activity Change Since 2001 | Gas production declined by roughly an order of magnitude by 2017 |
| Lead Researcher | David Jewitt — University of California, Los Angeles |
| Published In | The Astronomical Journal — March 2026 |
| Forecast | Continued spin instability may lead to fragmentation or full disintegration |
These jets started to push against the comet’s current rotation because they were dispersed unevenly across its surface. It completed a full rotation approximately every 20 hours, according to observations made in March 2017 by the Discovery Channel Telescope at Lowell Observatory in Arizona. Rotation had extended to between 46 and 60 hours by May, according to data from NASA’s Neil Gehrels Swift Observatory. The comet was now moving at almost a crawl.
The study’s principal investigator, David Jewitt of UCLA, sought an analogy that anyone who has spent time near a playground could comprehend. “It’s like pushing a merry-go-round,” he replied. “If it’s turning in one direction, and then you push against that, you can slow it and reverse it.” In theory, it’s fairly straightforward. Extraordinary in practice, as Hubble discovered in December 2017 that 41P had apparently passed through a period of nearly zero rotation, or nearly stopped in space, before the jets forced it into a spin that was almost exactly the opposite of where it had begun, completing a rotation in roughly 14 hours. During a single close solar passage, the entire reversal took place. That is nearly instantaneous on a cosmic timescale.
The information it provides about how small solar system bodies actually respond to persistent, uneven forces elevates this beyond mere curiosity. It was believed that the majority of comet structural changes would occur over centuries, if not longer, and that any one human lifetime would only provide the faintest glimpse of the process. Comet 41P significantly shortened that timeline, providing scientists with something truly unique: physical evolution that could be seen during the course of a human lifetime. The comet’s total gas production has decreased by about an order of magnitude since its 2001 perihelion, according to the study, indicating that its surface is being exhausted or covered in layers of insulating dust—wearing out, in a sense, more quickly than anticipated.
Sitting with all of this, one gets the impression that 41P is a tiny object with surprisingly big ramifications. Regarding the direction he believes it will go, Jewitt was quite direct: “I expect this nucleus will very quickly self-destruct.” If the spin changes continue unchecked, the comet may be torn apart by centrifugal stress that is greater than what its weak gravity and brittle structure can withstand. The comet has survived 1,500 years in its current orbit, so it’s still unclear exactly when that might occur, but the evidence’s trajectory suggests that something is unstable. It is an odd and strangely moving experience to watch a comet inch toward its own unraveling, captured in real time by a telescope that wasn’t even built with this question in mind.
