The image of a lump of rock and ice that is only a kilometer across tumbling through the inner solar system and then, in defiance of everything that seemed intuitively correct, stopping its own spin and beginning again in the opposite direction is almost disorienting. Not a model for a computer. Not a hypothetical forecast. An actual event that occurred in 2017 while NASA’s Hubble Space Telescope was in the area.
The object is comet 41P/Tuttle–Giacobini–Kresák, a tiny, battered traveler from the outer reaches of the solar system that swings through the inner neighborhood every 5.4 years. Jupiter’s gravity long ago pushed it into its current path. It’s not as well-known as Halley’s comet, which has its own postage stamps and folklore. Forty-one-P is more likely to appear in footnotes. Up until now. The results, which were published in The Astronomical Journal in late March, describe a confirmed spin reversal caused by the comet’s own outgassing jets, which no one had previously recorded in the history of comet observation.
Comet 41P/Tuttle–Giacobini–Kresák — Key facts
| Full designation | 41P/Tuttle–Giacobini–Kresák |
| Classification | Jupiter-family comet (short-period) |
| Orbital period | 5.4 years |
| Origin | Likely the Kuiper Belt; redirected by Jupiter’s gravity into the inner solar system |
| Nucleus size | ~0.6 miles (≈1 km) across — roughly three times the height of the Eiffel Tower |
| Key 2017 event | Rotation slowed from ~14-hour period (March) to 46–60 hours (May), then reversed; by December 2017, spinning again at ~14 hours |
| Cause of reversal | Asymmetric outgassing jets acting as natural thrusters against original rotation direction |
| Telescopes used | NASA Hubble Space Telescope, Neil Gehrels Swift Observatory, Lowell Discovery Telescope (Arizona) |
| Lead researcher | David Jewitt, planetary scientist, University of California, Los Angeles |
| Published in | The Astronomical Journal, March 2026 |
| Prognosis | Likely self-destruction — rapid spin expected to generate centrifugal forces that tear the nucleus apart |
There is a subtle charm to the tale of how this discovery was made. David Jewitt, a planetary scientist at UCLA, was searching through the Mikulski Archive for Space Telescopes — a digital library of Hubble data that accumulates observations the way a university basement accumulates old journals — when he came across images of 41P taken in December 2017. When combined with previous observations from NASA’s Swift Observatory and the Lowell Discovery Telescope in Arizona, what he discovered there revealed an odd and nearly paradoxical tale. The comet had been spinning once every fourteen hours in March 2017. It had drastically slowed to between 46 and 60 hours per rotation by May, which is roughly three times slower. By December, it was spinning quickly once more, at about 14 hours. But in the opposite direction this time.
For those who believed space physics was a well-established field, Jewitt’s elegant explanation of what transpired may be a little depressing. As 41P approached the Sun, frozen gases on its surface began to sublimate and vent into space as jets. Those jets, if unevenly distributed across the nucleus, act like tiny thrusters — pushing against the comet’s natural rotation until the spin slows, halts, and eventually reverses. Jewitt stated, “It’s like pushing a merry-go-round,” in the NASA press release. “If it’s turning in one direction, and then you push against that, you can slow it and reverse it.” As a metaphor, it’s fairly straightforward. remarkable as a physical occurrence that was witnessed.
The comet’s size, or rather its smallness, is part of what allowed for the observation of this at all. At roughly 0.6 miles across, or about three Eiffel Towers stacked end to end, 41P is exceptionally easy to torque. Those jet forces would have been much more stubbornly resisted by a larger body. Smaller comets may simply be more susceptible to spin reversals, which may occur more frequently than scientists have thought. It may take years of focused observation to start answering that question, which is still genuinely open.
As this narrative progresses, it seems as though astronomy is constantly reminding us of the messiness that lies beneath the neat diagrams found in textbooks. The comet’s overall activity has also declined sharply since earlier approaches — its gas production by 2017 was roughly ten times lower than during its 2001 perihelion pass, suggesting its volatile surface materials are running out or getting buried under insulating layers of dust. Like comets, it is aging. And the fast spin it’s now carrying may be the thing that finishes it. Jewitt has said he expects the nucleus to “very quickly self-destruct,” centrifugal forces eventually pulling it apart. A comet that was destroyed by its own exhaust after surviving billions of years in the outer solar system. That has an almost poetic quality, though sobering might be a better term.
