A team of scientists using NASA’s Hubble Space Telescope have witnessed for the first time the disintegration of an asteroid.

Fragile comets, comprised of ice and dust, have been seen falling apart as they near the Sun, but nothing like this has ever before been observed in the asteroid belt.

“Seeing this rock fall apart before our eyes is pretty amazing,” said Prof David Jewitt from the University of California, Los Angeles, who is the lead author of a paper published in the Astrophysical Journal Letters (arXiv.org).

The asteroid, named P/2013 R3, is as an anomalous, fuzzy-looking object. It was first discovered on September 15, 2013 by astronomers using the Catalina and Pan-STARRS Sky-Survey Telescopes. Follow-up observations revealed three co-moving bodies embedded in a dusty envelope that is nearly the diameter of Earth.

The Hubble Space Telescope then revealed that there were really 10 embedded objects, each with comet-like dust tails.

The four largest rocky fragments are up to 180 m in radius. The observations showed that the fragments are drifting away from each other at a leisurely pace of 1.6 km per hour.

The asteroid began coming apart early last year, but new pieces continue to emerge in the most recent images.

It is unlikely the asteroid is disintegrating because of a collision with another asteroid, which would have been instantaneous and violent by comparison to what has been observed. Debris from such a high-velocity smashup would also be expected to travel much faster than observed. Nor is the asteroid coming unglued due to the pressure of interior ices warming and vaporizing.

The asteroid is too cold for ices to significantly sublimate, and it has presumably maintained its nearly 480 million-km distance from the Sun for much of the age of the Solar System.

This leaves a scenario in which the asteroid is disintegrating due to a subtle effect of sunlight, which causes the rotation rate of the asteroid to gradually increase. Eventually, its component pieces succumb to centrifugal force and gently pull apart. The possibility of disruption in this manner has been discussed by scientists for several years, but never reliably observed.

For this scenario to happen, the asteroid must have a weak, fractured interior, probably as the result of numerous ancient but non-destructive collisions with other asteroids.

Most small asteroids, in fact, are thought to have been severely damaged in this way, giving them a “rubble pile” internal structure.

P/2013 R3 itself is probably the product of collisional shattering of a bigger body some time in the last billion years.

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David Jewitt et al. 2014. Disintegrating Asteroid P/2013 R3. ApJ 784, L8; doi: 10.1088/2041-8205/784/1/L8