Astronomers have witnessed for the first time the breakup of an asteroid into as many as 10 smaller pieces.
Comet nuclei have been seen falling apart as they near the sun but nothing like this type of breakup has been observed before in the asteroid belt.
NASA’s Hubble Space Telescope photographed the demolition and the discovery is published tody in Astrophysical Journal Letters.
“Seeing this rock fall apart before our eyes is pretty amazing,” said David Jewitt, a professor in the UCLA Department of Earth, Planetary and Space Sciences and the UCLA Department of Physics and Astronomy, who led the astronomical forensics investigation.
The crumbling asteroid, designated P/2013 R3, was first noticed as a fuzzy-looking object on September 15 last year by the Catalina and Pan-STARRS sky-survey telescopes.
A follow-up observation on October 1 with the W.M. Keck telescope on Hawaii’s Mauna Kea revealed three co-moving bodies embedded in a dusty envelope that is nearly the diameter of Earth.
“The Keck telescope showed us that this asteroid was worth looking at with Hubble,” Jewitt said.
The Hubble telescope revealed that there were really 10 embedded objects, each with comet-like dust tails. The four largest rocky fragments are up to 200 metres in radius.
The Hubble data showed that the fragments are drifting away from each other at a leisurely pace, slower than a strolling human. The asteroid began coming apart early last year, but new pieces continue to emerge in the most recent images.
This makes it unlikely that the asteroid is disintegrating because of a collision with another asteroid, which would be instantaneous and violent.
Nor is the asteroid coming unglued due to the pressure of interior ices warming and vapourising, Jewitt said.
This leaves a scenario in which the asteroid is disintegrating due to a subtle effect of sunlight, which causes the rotation rate to slowly increase.
Eventually, its component pieces like grapes on a stem gently pull apart due to centrifugal force, Jewitt said.
With Hubble’s recent discovery of an active asteroid spouting six tails (P/2013 P5), astronomers are seeing more circumstantial evidence that the pressure of sunlight may be the primary force that disintegrates small asteroids.
The asteroid’s remnant debris, weighing in at 200,000 tonnes, will provide a rich source of meteoroids, Jewitt said.
Most will eventually plunge into the sun, but a small fraction of the debris may one day enter the Earth’s atmosphere to blaze across the sky as meteors, he said.