An asteroid the size of Chicago’s Sears Tower that could one day slam into Earth keeps spinning faster, scientists have warned.
As the 510 metre asteroid, known as Bennu, moves through space at about 63,000 miles per hour, it also spins, completing a full rotation every 4.3 hours.
But scientists working on NASA’s OSIRIS-REx mission to the space rock claim that Bennu’s rotation rate is speeding up by about 1 second each 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 sound 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.
“As it speeds up, things ought to change, and so we’re going to be looking for those things,” said Mike Nolan, senior research scientist at the Lunar and Planetary Laboratory at the University of Arizona.
“Detecting this speed up gives us some clues as to the kinds of things we should be looking for.”
The idea that the rotation of asteroids could speed up over time was first predicted around 2000, and first detected in 2007, but so far this acceleration has only been detected in a handful of asteroids.
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.
However, the OSIRIS-REx team suggests the reason for the increase in Bennu’s rotation is more likely due to a phenomenon known the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect.
This is caused by light from the Sun hitting the asteroid, and being 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.
Scientists claim Bennu has a 1 in 2,700 chance of striking Earth next century, between the years 2175 and 2199.
If the asteroid does hit our planet, it is estimated that the kinetic energy of this impact would be equivalent to 1,200 megatons – 80,000 times the energy of the Hiroshima bomb.
The OSIRIS-REx mission will determine Bennu’s rotation rate independently this year, which will help scientists nail down the reason for the increase in rotation.
Since spacecraft will never visit the vast majority of asteroids, the measurements will also help scientists learn how well ground-based measurements are able to understand these far-away objects.
“By testing these predictions in a few cases, we will significantly improve our confidence in predictions made for other objects,” the study’s authors write.