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SOHO
RAISES THE ANTE WITH DISCOVERY OF 500TH COMET
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Image
of the 500th comet - Click on the image for animation.
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Amateur
astronomers worldwide placed their bets, crossed their fingers
and waited in anticipation for the ESA-NASA Solar & Heliospheric
Observatory (SOHO) spacecraft to spot its 500th comet. Their
patience was rewarded on August 12 as SOHO, a mission actually
designed to research the Sun, revealed its own type of royal
flush with comet C/2002 P3 (SOHO).
It
is the 500th comet to be discovered by SOHO since it launched
on December 2, 1995, making the spacecraft by far the most
prolific comet-hunting observatory in history.
Between
May 2 and May 31, using the SOHO website, 1,256 amateur astronomers
tracked SOHO's observations of comets and made predictions
about the date and time that the 500th comet would be at perihelion
(the closest approach to the Sun). Comet C/2002 P3 (SOHO)
had a perihelion time of August 12 at 12:04:48 p.m. EST.
Diane
McElhiney won the sweepstakes with a prediction only one hour
and 43 minutes away from the correct time.
The
website also allows comet aficionados around the world to
look at real-time SOHO data and images. Once they see what
appears to be a new comet, they seek confirmation from others
on-line. If confirmation is provided, they have accomplished
a feat that is the goal of many amateur astronomers.
More
than 75 percent of the comet discoveries have come from amateurs
from Australia, Canada, China, France, Germany, Italy, Lithuania,
Russia, the United Kingdom and the United States.
"Analyzing
SOHO data is a great challenge and you have to combine many
skills," said Rainer Kracht, the discoverer of C/2002
P3 (SOHO). "But every amateur astronomer dreams of finding
a comet."
Kracht,
a mathematics, physics, computer science and astronomy teacher
at the Kooperative Gesamtschule Elmshorn in Elmshorn, Germany,
has discovered 63 comets since August 2001 with the help of
SOHO data and images. An entire group of near Sun comets that
he discovered is even named after him - the Kracht group.
C/2002
P3 (SOHO) is not only an unanticipated milestone for the mission,
but whereas most near Sun comets are of the Kreutz family,
C/2002 P3 (SOHO) is a member of a family of comets called
the Meyer group. The Meyer group is one of three new families
that have been discovered with SOHO data. A comet family is
a group of comets that originated from the same place and
follow the same path. C/2002 P3 (SOHO) has a perihelion distance
of 5.37 million km from the Sun.
"We
don't yet know much about this family, or the other new families,"
said Dr. Doug Biesecker, the head of SOHO's comet discovery
program stationed at NASA's Goddard Space Flight Center and
a solar physicist with L3 Com Analytics Corporation. "With
such few known members of this family, we need every additional
comet we can get."
The
use of SOHO as a tool to discover comets is a byproduct of
the mission's original purpose - to continuously monitor solar
weather and assist scientists in analyzing how the Sun functions.
The Large Angle and Spectrometric Coronagraph (LASCO), one
of the instruments on SOHO, blocks out the Sun to create an
artificial eclipse and then views the space around the Sun,
looking for outbursts of solar activity. This eclipse allows
the Sun's faint outer atmosphere (corona) to be seen and studied.
Like
the corona, comets that would usually be lost in the glare
of the Sun unexpectedly come into LASCO's field of view. Almost
all of them end up vaporized in the solar atmosphere. In spite
of the fact that the SOHO Kreutz family comets tend to be
only 10 meters in diameter, they are fragments of a comet
that was originally much larger, maybe 100 km in diameter.
This is so large, in fact, that it might have been visible
during daylight more than 2000 years ago.
"Though
LASCO was not originally built for this purpose, no other
instrument has discovered more of these comets," said
Dr. Bernhard Fleck, ESA Project Scientist for SOHO stationed
at Goddard. "It was a wonderful surprise, of the kind
we get in science sometimes."
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