SUSPECTED ASTEROID COLLISION LEAVES TRAILING DEBRISWASHINGTON -- NASA
NASA's Hubble Space Telescope has observed a mysterious
X-shaped debris pattern and trailing streamers of dust that suggest a
head-on collision between two asteroids. Astronomers have long
thought the asteroid belt is being ground down through collisions,
but such a smashup has never been seen before.
Asteroid collisions are energetic, with an average impact speed of
more than 11,000 miles per hour, or five times faster than a rifle
bullet. The comet-like object imaged by Hubble, called P/2010 A2, was
first discovered by the Lincoln Near-Earth Asteroid Research, or
LINEAR, program sky survey on Jan. 6. New Hubble images taken on Jan.
25 and 29 show a complex X-pattern of filamentary structures near the
nucleus.
"This is quite different from the smooth dust envelopes of normal
comets," said principal investigator David Jewitt of the University
of California at Los Angeles. "The filaments are made of dust and
gravel, presumably recently thrown out of the nucleus. Some are swept
back by radiation pressure from sunlight to create straight dust
streaks. Embedded in the filaments are co-moving blobs of dust that
likely originated from tiny unseen parent bodies."
Hubble shows the main nucleus of P/2010 A2 lies outside its own halo
of dust. This has never been seen before in a comet-like object. The
nucleus is estimated to be 460 feet in diameter.
Normal comets fall into the inner regions of the solar system from icy
reservoirs in the Kuiper belt and Oort cloud. As comets near the sun
and warm up, ice near the surface vaporizes and ejects material from
the solid comet nucleus via jets. But P/2010 A2 may have a different
origin. It orbits in the warm, inner regions of the asteroid belt
where its nearest neighbors are dry rocky bodies lacking volatile
materials.
This leaves open the possibility that the complex debris tail is the
result of an impact between two bodies, rather than ice simply
melting from a parent body.
"If this interpretation is correct, two small and previously unknown
asteroids recently collided, creating a shower of debris that is
being swept back into a tail from the collision site by the pressure
of sunlight," Jewitt said.
The main nucleus of P/2010 A2 would be the surviving remnant of this
so-called hypervelocity collision.
"The filamentary appearance of P/2010 A2 is different from anything
seen in Hubble images of normal comets, consistent with the action of
a different process," Jewitt said. An impact origin also would be
consistent with the absence of gas in spectra recorded using
ground-based telescopes.
The asteroid belt contains abundant evidence of ancient collisions
that have shattered precursor bodies into fragments. The orbit of
P/2010 A2 is consistent with membership in the Flora asteroid family,
produced by collisional shattering more than 100 million years ago.
One fragment of that ancient smashup may have struck Earth 65 million
years ago, triggering a mass extinction that wiped out the dinosaurs.
But, until now, no such asteroid-asteroid collision has been caught
"in the act."
At the time of the Hubble observations, the object was approximately
180 million miles from the sun and 90 million miles from Earth. The
Hubble images were recorded with the new Wide Field Camera 3 (WFC3),
which is capable of detecting house-sized fragments at the distance
of the asteroid belt.
For Hubble images and more information, visit:
http://www.nasa.gov/hubble
