[meteorite-list] LARGE COMET GIVES BIRTH TO SMALL COMETS

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 16 Sep 2009 23:38:27 -0500
Message-ID: <5B1F5226CAED47579C1B478DE8904BB1_at_ATARIENGINE2>

    I've always assumed that small comet
fragments came from the complete breakup of
the parent comet (didn't you?). But it appears
that comets can produce many, many small
comets without suffering any apparent harm.
Or maybe this is the way comets break up...
slowly?

Sterling K. Webb
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http://www.space.com/scienceastronomy/090915-mini-comets.html

Comet Outburst Spawns Mini-Comets
posted: 15 September 2009

A comet recently spewed out a cluster of mini comets
in a huge outburst that was the largest ever witnessed
by astronomers.

A team of researchers began observing the comet
17P/Holmes in October 2007, after it was reported
that the object, about 2.2 miles wide (3.6 km wide),
had brightened by a million times in less than a day.

UCLA researcher Rachel Stevenson and colleagues
noted multiple fragments flying rapidly away from
the comet's nucleus. They continued observing
for several weeks after the outburst using the
Canada-France-Hawaii Telescope in Hawaii and
watched as the dust cloud ejected by the comet
grew to be larger than the sun.

The astronomers examined a sequence of images
taken over nine nights using a digital filter that
enhances small features. They found numerous
tiny objects that moved away from the nucleus
at speeds of up to 280 mph (125 meters per second).
These objects were too bright to simply be bare
rocks, but instead were more like mini comets,
creating their own dust clouds as ice on their
surfaces sublimated directly to vapor.

"Initially we thought this comet was unique simply
because of the scale of the outburst," Stevenson said.
"But we soon realized that the aftermath of the
outburst showed unusual features, such as these
fast-moving fragments, that have not been detected
around other comets."

Although the outburst was impressive in the
telescope images, it wasn't visible to the naked eye.

Scientists aren't sure of the exact cause of the outburst.
Possibly, pressure inside the comet built up as it moved
closer to the sun, until eventually part of the surface
broke away, releasing a huge cloud of dust and gas,
as well as larger fragments.

Even after ejecting mini comets, the solid nucleus of
comet Holmes survived and continued on its orbit,
seemingly unperturbed.

Holmes takes about 6 years to circle the sun, and
travels between the inner edge of the asteroid belt
to beyond Jupiter. The comet is now moving away
from the sun but will return to its closest approach
in 2014, when astronomers will examine it for signs
of further outbursts.
Received on Thu 17 Sep 2009 12:38:27 AM PDT