Asteroid P/2013 R3
NASA's Hubble Space Telescope has photographed the never-before-seen breakup of an asteroid into as many as 10 smaller pieces.
Though fragile comet nuclei have been seen falling apart as they near
the Sun, nothing like this breakup has ever before been observed in the
asteroid belt.
"This is a rock. Seeing it fall apart before our eyes is pretty
amazing," said David Jewitt of UCLA, who led the astronomical forensics
investigation.
The crumbling asteroid, designated P/2013 R3, was first noticed as an
anomalous, fuzzy-looking object on Sept. 15, 2013, by the Catalina and
Pan-STARRS sky surveys. A follow-up observation on October 1 with the W.
M. Keck Observatory on the summit of Mauna Kea, Hawaii revealed three
co-moving bodies embedded in a dusty envelope that is nearly the
diameter of Earth.
"Keck showed us that this thing was worth looking at with Hubble,"
Jewitt said. With its superior resolution, Hubble observations soon
showed that there were really 10 embedded objects, each with comet-like
dust tails. The four largest rocky fragments are up to 200 yards in
radius, about twice the length of a football field.
The Hubble data showed that the fragments are drifting away from each
other at a leisurely one mile per hour — slower than the speed of 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 by comparison to what has been observed. Some of the 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
300-million-mile 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 to slowly
increase. Eventually, its component pieces, like grapes on a stem,
gently pull apart due to centrifugal force. The possibility of
disruption by this so-called YORP torque has been discussed by
scientists for several years but, so far, never reliably observed.
For this to happen, P/2013 R3 must have a weak, fractured interior,
probably as the result of numerous, ancient, 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.
With the previous 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 (less than a mile across) in the solar system.
The asteroid's remnant debris, weighing in at 200,000 tons, will in
the future provide a rich source of meteoroids. Most will eventually
plunge into the Sun but a small fraction of the debris may one day hit
the Earth to blaze across the sky as meteors.
CONTACT
Donna Weaver / Ray VillardSpace Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Source: HubbleSite