[meteorite-list] Solar Storms Smack a Comet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Dec 6 12:35:35 2004
Message-ID: <200412061735.JAA03020_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/mystery_monday_041206.html

Solar Storms Smack a Comet
By Tariq Malik
space.com
6 December 2004

Astronomers have pieced together what appears to be the first direct
evidence that solar storms can wreck havoc with comets, destroying the
ion tails of icy wanderers in a collision of highly charged particles.

But the effect is not permanent and may serve as a marker for scientists
trying to track solar storms known as coronal mass ejections (CMEs) as
they blow out into space.

"What we have now is sort of a new tool of tracking these ejections,"
said Geraint Jones, co-investigator of the comet study and a researcher
at NASA's Jet Propulsion Laboratory. "It's like dropping paint into a
flowing river of water."

The ion tails of comets constantly stream away from the Sun, pushed back
by solar wind blowing at about 894,774 mph (400 kilometers per second).
But the charged particles of CMEs, among the worst of solar storms, can
slam into a comet's ion tail at about 2.2 million mph (1,000 kilometers
per second), causing kinks, scalloped patterns or disrupting the tail
altogether, Jones' research found.

"We're still far from having a full understanding of what's going on
[with CMEs]," Jones told SPACE.com.

But by watching comet tail behavior, researchers could learn more about
changes in CME structure and speed as they move through space,
researchers added.

"When [CMEs] move outward we know there's a lot of change, but that's
it," explained Douglas Biesecker, a physicist with the Space Environment
Center at the National Oceanic and Atmospheric Administration (NOAA).
"It would be a little more useful if there were a lot more comets out
there."

The study, conducted by Jones and his colleague John Brandt at the
University of New Mexico, appeared in the online version of the journal
Geophysical Research Letters and will appear in the journal's upcoming
print edition.

Comet distortion

At the heart of Jones' study is the comet 153P/Ikeya-Zhang, which passed
through the inner solar system during spring 2002.

Jones and Brandt were able to identify specific interactions between
CMEs and Ikeya-Zhang's ion tail by combining data from the
sun-watching NASA/European Space Agency SOHO spacecraft and
observations collected by amateur astronomers.

CME events recorded by SOHO instruments on March 2, March 9-10 and April
17 appear to have slammed into Ikeya-Zhang's ion tail each about a day
or so after leaving the Sun. None of the CMEs distorted the comet's tail
for more than an hour.

"On their own, the images were fascinating," Jones said. "But it was
only when we put them all together that we saw how the changes were
occurring that we realized what was happening."

Past observations had suggested that CMEs belched from the Sun could
impact a comet's ion tail, including some stunning images
taken by the SOHO spacecraft last year.

During February 2003, SOHO caught the comet C/2002 V1 NEAT swing by the
Sun during a CME event, which researchers believed caused a kink in the
icy wanderer's tail. The catch was a fortunate one, since NEAT's orbit
brought it close to the Sun in astronomical terms, about one-tenth the
distance between the Earth and the star or 0.1 astronomical unit
(AU). One AU is about 93 million miles (150 million kilometers).

But Ikeya-Zhang's closest approach was about five times farther out
at 0.51 AU at a distance where sun-watching spacecraft like SOHO can't see.

"Our studies have been limited in the past because we're limited to
observations from spacecraft that are just measuring what the solar
activity is near the Sun," Jones said.

Some instruments, such as the Solar Mass Ejection Imager aboard the
Coriolis spacecraft in Earth orbit and the planned
STEREO observatories are seeking a wider view on CMEs, Biesecker added.

Amateur assets

Part of the success behind the Jones-Brandt study is due to the readily
available network of amateur astronomers from around the world, which
heeded an open call for observations when Ikeya-Zhang swung past the Sun.

"Without the amateur astronomers, this research would not have been
possible," Jones said. "It's a great example of how amateur astronomers
and professionals can work together."

Jones hopes that cooperation will be repeated with a pair of comets that
were observed earlier this year.

"They have more telescope time to themselves then we have sometimes as
professional astronomers," said Biesecker of amateur skywatchers.
Received on Mon 06 Dec 2004 12:35:16 PM PST