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

[Sterling K. Webb]

    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.