— An object imaged last week by the Hubble Space Telescope looks at
first glance to be a comet, but a closer examination indicates it is
something researchers have never seen before — the immediate aftermath
of two asteroids colliding.
The scattered debris that looks like a comet’s tail
is actually the result of two asteroids colliding nearly head-on at
more than 11,000 miles per hour, scattering pieces in all directions,
NASA announced earlier this week. The asteroid belt between Mars and
Jupiter, where the collision occurred, contains the remains of many
such events from the distant past, but this is first time that
researchers have observed such debris so soon after a collision.
The object, called P/2010 A2, was first observed
Comets are icy bodies that fall into the inner solar
system from distant reservoirs in the Kuiper Belt and Oort Cloud. As
they warm up, they shed particles and water vapor that are pushed away
from the comet in a smooth tail by solar pressure.
But spectra of P/2010 A2 show no gases associated
with the object, indicating there is no water present. The main body of
the object, which is about 460 feet in diameter, lies separate from the
“tail,” and the tail itself shows an unusual filamentous structure that
includes a large X-shaped portion.
The most likely explanation, said principal investigator
is that 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 presence of sunlight.
Based on the length of the tail, about 100,000 miles, the collision probably happened just a few months ago, Jewitt said.
The orbit of the object suggests that it is part of
the Flora asteroid family, a group produced by other collisions more
than 100 million years ago. One former member of the family is thought
to be the asteroid that struck Earth 65 million years ago, creating a
global cooling that caused dinosaurs to become extinct.
When observed by Hubble, P/2010 A2 was about 180 million miles from the sun and 90 million miles from Earth.
In addition to the image being “a super-cool thing
to look at,” Jewitt said, “it will help us understand the physics of
the breakup of a body in space. That’s almost unexplored, but it is
something we want to know about” because of the likelihood that a large
asteroid will eventually approach Earth and need to be destroyed.
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