Comet Slowed Down and Then Began Rotating in the Opposite Direction

Data from the Hubble Space Telescope indicates that comet 41P/Tuttle—Giacobini—Kresák has undergone a complete reversal of its rotational direction. This represents the first observed instance of a comet reversing its spin, providing latest data on the physical dynamics of small bodies within the solar system.

Mechanisms of Rotational Change

The shift in rotation is driven by the process of sublimation, where ice on the comet’s surface transitions directly from a solid to a gas due to solar radiation. As this gas and dust are expelled from the nucleus, the resulting streams act as jet engines, exerting force that can alter the rotation of the comet’s core.

Because comet 41P/Tuttle—Giacobini—Kresák possesses a relatively small nucleus—estimated at approximately one kilometer in size—it has weak gravitational stability. This makes the object particularly susceptible to the torque generated by outgassing, allowing external physical processes to dominate its rotational inertia.

Observations and Timeline

Analysis of the comet’s behavior reveals a distinct sequence of rotational changes. Observations conducted in 2017 showed a sharp deceleration in the comet’s spin, with the rotation period extending from a few dozen hours to more than 50 hours.

Following this period of slowing, further research showed the comet began to accelerate again. The rotation period eventually decreased to approximately 14 hours. Researchers concluded that the most consistent interpretation of this data is that the comet’s rotation nearly stopped entirely before restarting in the opposite direction.

The study of 41P/Tuttle—Giacobini—Kresák highlights how the interaction between solar radiation and volatile surface materials can fundamentally change the physical orientation of small celestial bodies.