[meteorite-list] Comet Corpses in the Solar Wind

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 26 Jan 2012 10:10:59 -0800 (PST)
Message-ID: <201201261810.q0QIAxFR020267_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2012/20jan_cometcorpse/

Comet Corpses in the Solar Wind
NASA Science News
January 20, 2012

A paper published in today's issue of Science raises
an intriguing new possibility for astronomers: unearthing comet corpses
in the solar wind. The new research is based on dramatic images of a
comet disintegrating in the sun's atmosphere last July.

Comet Lovejoy grabbed headlines in Dec. 2011 when it plunged into the
sun's atmosphere and emerged again relatively intact. But it was not
the first comet to graze the sun. Last summer a smaller comet took the
same trip with sharply different results. Comet C/2011 N3 (SOHO) was
completely destroyed on July 6, 2011, when it swooped 100,000 km above
the stellar surface. NASA's Solar Dynamics Observatory (SDO) recorded
the disintegration.

"For the first time, we saw a comet move across the face of the sun and
disappear," says Dean Pesnell, a co-author of the Science paper and
Project Scientist for SDO at the Goddard Space Flight Center. "It was
unprecedented."

In Jan. 20th issue of Science, the research team reported their
analysis of the SDO images.

A key finding was the amount of material deposited into the sun's
atmosphere. "The comet dissolved into more than a million tons of
electrically charged gas," says Pesnell. "We believe these vapors
eventually mixed with the solar wind and blew back into the solar system."

Pesnell says it might be possible to detect such "comet corpses" as they
waft past Earth. Comets are rich in ice (frozen H_2 O), so when they
dissolve in the hot solar atmosphere, the gaseous remains contain plenty
of oxygen and hydrogen. A solar wind stream containing extra oxygen
could be a telltale sign of a disintegrated comet. Other elements
abundant in comets would provide similar markers.

Comet corpses are probably plentiful. There's a busy family of comets
known as "Kreutz sungrazers," thought to be fragments of a giant comet
that broke apart hundreds of years ago. Every day or so, SOHO sees one
plunge into the sun and vanish. Each disintegration event creates a puff
of comet vapor that might be detectable by spacecraft sampling the solar
wind.

Why bother? Researchers are beginning to think of sungrazers as 'test
particles' for studying the sun's atmosphere--kind of like tossing rocks
into a pond. A lot can be learned about the pond by studying the ripples.

Indeed, SDO observed some extraordinary interactions between the sun and
the doomed comet. As C/2011 N3 (SOHO) moved through the hot corona,
cold gas lifted off the comet's nucleus and rapidly (within minutes)
warmed to more than 500,000K, hot enough to shine brightly in SDO's
extreme ultraviolet telescopes.

"The evaporating comet gas was glowing as brightly as the sun behind
it," marvels Pesnell.

The gas was also rapidly ionized by a process called "charge exchange,"
which made the gas responsive to the sun's magnetic field. Caught in the
grip of magnetic loops which thread the solar corona, the comet's
ionized tail wagged back and forth wildly in the moments before final
disintegration.

Watching this kind of sun-comet interaction could reveal new things
about the thermal and magnetic structure of the solar atmosphere.
Likewise, measuring how long it takes for "comet corpses" to reach
Earth, and then sampling the gases when they arrive, could be very
informative.

"Before SDO, no one dreamed we could observe a comet disintegrate inside
the sun's atmosphere," says Pesnell who confesses that even he was a
skeptic. But now, "I'm a believer."

The original research described in this story may be found in the Jan.
20th edition of Science: Destruction of Sun-grazing comet C/2011 N3
(SOHO) <http://www.sciencemag.org/content/335/6066/324> by C. J.
Schrijver, J. C. Brown, K. Battams, P. Saint-Hilaire, W. Liu, H. Hudson,
and W. D. Pesnell


Author:Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Thu 26 Jan 2012 01:10:59 PM PST