COMETS • ROTATION • ARCHIVAL DISCOVERY
Comet 41P: Evidence of a Spin Reversal
Escaping gas can change a small world’s rotation—and perhaps its future.
ADDED OCTOBER 28, 2026 • NASA RELEASE MARCH 26, 2026 • OBSERVATIONS FROM 2017
The evidence
David Jewitt analyzed archival Hubble observations of 41P/Tuttle–Giacobini–Kresák from December 2017. Brightness variations support a rotation period of 0.60 ± 0.01 days—about 14.4 hours. Earlier Swift measurements indicated 46–60 hours. The study interprets this change as a likely reversal driven by outgassing torque.
The nucleus’s effective radius is estimated at 500 ± 100 meters. Its small size makes outgassing particularly important to its rotational evolution.
How gas jets can turn a comet
Solar heating causes ice to become gas and escape. Uneven jets exert torque: a turning effect. A persistent torque opposing the original spin can slow rotation through zero and build rotation in the other direction.
Spin is different from orbit
“Backward” refers to rotation about the comet’s own axis. It does not mean the comet reversed its path around the Sun.
Observation, interpretation and prediction
| Evidence level | What the claim means |
|---|---|
| Measurements | Rotation-period estimates changed dramatically during 2017. |
| Interpretation | Reversal offers a natural explanation of the combined measurements; the transition was not continuously filmed. |
| Prediction | Further spin-up could destabilize the nucleus, causing fragmentation. |
Will it self-destruct?
NASA reports Jewitt’s expectation of rapid future destruction, but this is not a witnessed breakup or a firm countdown. The paper notes that unusually strong activity could make estimated lifetimes too short; alternatively, the present nucleus may be a remnant of a larger body. Future activity matters.
Why it belongs in MKP
MKP perspective: This story connects a familiar physics idea—torque—with a changing natural object. It also shows why old observations remain valuable: a later question can reveal meaning in an existing dataset.
Discussion prompts
Why would a push through an object’s center change its motion differently from a push off-center? Which observations would best test the spin-reversal interpretation? What evidence would turn a breakup prediction into an observed event?
Discuss comet dynamics →Primary sources
- Jewitt, D. (2026). Reversal of Spin: Comet 41P/Tuttle–Giacobini–Kresak. The Astronomical Journal. Author manuscript and abstract.
- NASA: Hubble Detects First-Ever Spin Reversal of Tiny Comet — March 26, 2026.
- NASA’s explanatory animation — labeled visualization.