[meteorite-list] Comet Lovejoy Plunges into the Sun and Survives

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 16 Dec 2011 11:01:19 -0800 (PST)
Message-ID: <201112161901.pBGJ1JoT017357_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2011/16dec_cometlovejoy/

Comet Lovejoy Plunges into the Sun and Survives
NASA Science News
December 16, 2011

This morning, an armada of spacecraft witnessed
something that many experts thought impossible. Comet Lovejoy flew
through the hot atmosphere of the sun and emerged intact.

"It's absolutely astounding," says Karl Battams of the Naval Research
Lab in Washington DC. "I did not think the comet's icy core was big
enough to survive plunging through the several million degree solar
corona for close to an hour, but Comet Lovejoy is still with us."

The comet's close encounter was recorded by at least five spacecraft:
NASA's Solar Dynamics Observatory and twin STEREO probes, Europe's
Proba2 microsatellite, and the ESA/NASA Solar and Heliospheric
Observatory. The most dramatic footage so far comes from SDO, which saw
the comet go in (movie
<http://science.nasa.gov/media/medialibrary/2011/12/16/comet_whoosh.m4v>)
and then come back out again (movie
<http://science.nasa.gov/media/medialibrary/2011/12/16/lovejoyemerges.m4v>).

In the SDO movies, the comet's tail wriggles wildly as the comet plunges
through the sun's hot atmosphere only 120,000 km above the stellar
surface. This could be a sign that the comet was buffeted by plasma
waves coursing through the corona. Or perhaps the tail was bouncing
back and forth off great magnetic loops known to permeate the sun's
atmosphere. No one knows.

"This is all new," says Battams. "SDO is giving us our first look^1 at
comets travelling through the sun's atmosphere. How the two interact is
cutting-edge research."

"The motions of the comet material in the sun???s magnetic field are just
fascinating," adds SDO project scientist Dean Pesnell of the Goddard
Space Flight Center. "The abrupt changes in direction reminded me of
how the solar wind affected the tail of Comet Encke in 2007 (movie
<http://science.nasa.gov/science-news/science-at-nasa/2007/01oct_encke/>)."

Comet Lovejoy was discovered on Dec. 2, 2011, by amateur astronomer
Terry Lovejoy of Australia. Researchers quickly realized that the new
find was a member of the Kreutz family of sungrazing comets. Named
after the German astronomer Heinrich Kreutz, who first studied them,
Kreutz sungrazers are fragments of a single giant comet that broke apart
back in the 12th century (probably the Great Comet of 1106). Kreutz
sungrazers are typically small (~10 meters wide) and numerous. The Solar
and Heliospheric Observatory sees one falling into the sun every few days.

At the time of discovery, Comet Lovejoy appeared to be at least ten
times larger than the usual Kreutz sungrazer, somewhere in the in the
100 to 200 meter range. In light of today's events, researchers are
re-thinking those numbers.

"I'd guess the comet's core must have been at least 500 meters in
diameter; otherwise it couldn't have survived so much solar heating,"
says Matthew Knight. "A significant fraction of that mass would have
been lost during the encounter. The remains are probably much smaller."

SOHO and NASA's twin STEREO probes are monitoring the comet as it
recedes from the sun. It is still very bright and should remain in range
of the spacecrafts' cameras for several days to come.

What happens next is anyone's guess.

"There is still a possibility that Comet Lovejoy will start to
fragment," continues Battams. "It's been through a tremendously
traumatic event; structurally, it could be extremely weak. On the other
hand, it could hold itself together and disappear back into the recesses
of the solar system."

"It's hard to say," agrees Knight. "There has been so little work on
what happens to sungrazing comets after perihelion (closest approach).
This continues to be fascinating."


Author:Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Fri 16 Dec 2011 02:01:19 PM PST