For many years, a rare class of so-called “active asteroids” that appear to throw off a trail of dust and debris like a comet have puzzled scientists. In 2010, a new sub-type of active asteroid was discovered that appeared to spontaneously eject a shot of dust for no apparent reason. One of the popular explanations floated for the new phenomenon was that these asteroids were undertaking a radical form of cosmic weight loss called “rotational disruption. Basically, the idea was that these asteroids were spinning so fast that the centrifugal forces were able to exceed that of their own gravity and cause the asteroids to begin to break apart.
Finally, for the first time, a team of astronomers was able to observe an active asteroid suspected of going through rotational disruption and capture it after ejecting fragments of itself into space that continue to trail the asteroid like a comet’s tail.
“When we pointed Keck II (a large telescope on Hawaii’s Mauna Kea) at P/2012 F5 last August, we hoped to measure how fast it rotated and check whether it had sizable fragments. And the data showed us all that,” said Michal Drahus, of the Jagiellonian University in Poland, in a release.
At least four fragments of the object can be seen in its tail in the resulting images. The asteroid was known to have thrown off some debris in 2011, but it was initially too dusty when it was discovered for astronomers to get a good look. It now seems that the asteroid was once a larger object, but broke apart, leaving the existing smaller nucleus and its dusty tail.
The team also determined that P/2012 F5 has a very short rotation time of just 3.24 hours, which they say is “fast enough to cause the object to impulsively explode” and is currently the fastest measured among known active asteroids. “This is really cool because fast rotation has been suspected of catapulting dust and triggering fragmentation of some active asteroids and comets,” Drahus said. “But up until now we couldn’t fully test this hypothesis as we didn’t know how fast fragmented objects rotate.”
Drahus concedes that although the team’s data is consistent with the rotational disruption scenario, alternative explanations for the asteroid’s breakup, like a collision with a smaller object at high speeds, can’t be completely ruled out yet.