[meteorite-list] Hale-Bopp: The Comet That Doesn't Quit

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Mar 25 19:44:51 2005
Message-ID: <200503260044.j2Q0iTr05415_at_zagami.jpl.nasa.gov>

For JPL internal use only.

http://skyandtelescope.com/news/article_1486_1.asp

Hale-Bopp: The Comet That Doesn't Quit
By David Tytell
Sky & Telescope
May 25, 2005

Eight years after Comet Hale-Bopp dazzled astronomers
as it passed through the inner solar system, the dirty snowball is still
detectable (about 20th magnitude) despite being a whopping 21
astronomical units from the Sun. On January 8th MIT astronomers Andrew
S. Rivkin and Richard P. Binzel observed the comet with Magellan
Observatory's 6.5-meter Clay telescope in Chile.

Rivkin and Binzel were aiming for a "Goldilocks" observing moment - the
comet would have cooled off, the coma would be gone, and yet the nucleus
would still be bright enough to observe. "There's not a lot of spectra
of the nuclei of comets," says Rivkin. They are hard to capture because
the nucleii are obscured once comets develop comas. They didn't find
what they bargained for. "When we tried to see the nucleus," says
Rivkin, "the thing had a tail!"

Although they couldn't see the nucleus, the observations raised a key
question: why is Hale-Bopp still active? "Hale-Bopp is just acting like
a normal, bright, long-period comet," says Paul R. Weissman (NASA/Jet
Propulsion Laboratory). "Long-period comets stay active so far out that
one can never reliably say that we are looking at a bare nucleus."

Weismann says that comets like Hale-Bopp have far more volatile ices
close to their surfaces than short-period comets do, which can
contribute to activity at much greater distances. "It is not at all
surprising, now that the comet is far from the Sun, that there is still
enough energy to sublimate the CO (carbon monoxide) ices, even if they
are buried somewhat below the immediate surface," he adds. Even while on
perihelion approach, it takes a while for the Sun's heat to penetrate
into the nucleus's middle.

"It's just like cooking a steak - the longer you cook it, the warmer it
gets deep inside," says Weismann.
Received on Fri 25 Mar 2005 07:44:29 PM PST