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New research using ground-based observations has detected a slight increase over time in the daily rotation of the asteroid Bennu.
The new research finds the asteroid’s rotation is speeding up by about 1 second per century. In other words, Bennu’s rotation period is getting shorter by about 1 second every 100 years.
While the increase in rotation might not seem like much, over a long period of time it can translate into dramatic changes in the space rock. As the asteroid spins faster and faster over millions of years, it could lose pieces of itself or blow itself apart, according to the study’s authors.
…The change in Bennu’s rotation could be due to a change in its shape. Similar to how ice skaters speed up as they pull in their arms, an asteroid could speed up as it loses material.
Nolan and his co-authors suggest the reason for the increase in Bennu’s rotation is more likely due to a phenomenon known the YORP effect. Sunlight hitting the asteroid is reflected back into space. The change in the direction of the light coming in and going out pushes on the asteroid and can cause it to spin faster or slower, depending on its shape and rotation.
Truth is, this is not a very significant finding. Asteroids don’t weight much, and thus have very weak gravitational fields. It is therefore very easy to change their orbit and rotation, as well as add or subject material from them.
In this sense, the conclusion above is likely incorrect. What they have found is that the asteroid’s rotation increased at a pace of about 1 second per century, during their study period. Their data only covers the period from 1999 to 2005. Bennu could easily slowed its rotation, or increased it even more, during other times.