Why Toutatis tumbles

Two rotations at once, sunlight torques and what “daytime” would mean on a non-principal-axis rotator.

Published 2026-10-23

Earth spins around a fixed axis, so the Sun rises in the east every day. Toutatis does not work that way.^[2]

Two motions combined

Toutatis rotates around its long axis with a period of about 5.38 days, while that long axis itself precesses — swings around in a cone — every 7.38 days.^[2] The two periods don’t line up, so the overall motion never exactly repeats.

A chaotic sky

For someone standing on the surface, the Sun would appear to rise and set at seemingly random places on the horizon and at random times.^[2]

How did it start tumbling?

One explanation is the YORP effect: sunlight absorbed and re-emitted unevenly by an irregular surface exerts a tiny torque that changes an asteroid’s spin over time.^[5] Toutatis may have lost most of its original angular momentum this way and entered its tumbling state.^[2] YORP is also responsible for creating binary and tumbling asteroids in general.^[5]

Slow, by asteroid standards

JPL lists an effective period of about 176 hours — over a week — making Toutatis a very slow rotator compared with the few-hour spins of many asteroids.^[1]

Numbered citations link to the sources list on the Toutatis overview page.