[meteorite-list] History's Greatest Comet Hunter Approaches Major Milestone (SOHO)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jul 6 14:20:12 2005
Message-ID: <200507061819.j66IJNK15895_at_zagami.jpl.nasa.gov>

Dolores Beasley
Headquarters, Washington July 6, 2005
(Phone: 202/358-1753)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-5017)

RELEASE: 05-173

HISTORY'S GREATEST COMET HUNTER APPROACHES MAJOR MILESTONE

The Solar and Heliospheric Observatory (SOHO) spacecraft is
expected to discover its 1,000TH comet this summer.

The SOHO spacecraft is a joint effort between NASA and the
European Space Agency. It has accounted for approximately
one-half of all comet discoveries with computed orbits in
the history of astronomy.

"Before SOHO was launched, only 16 sun grazing comets had
been discovered by space observatories. Based on that
experience, who could have predicted SOHO would discover
more than 60 times that number, and in only nine years,"
said Dr. Chris St. Cyr. He is senior project scientist for
NASA's Living With a Star program at the agency's Goddard
Space Flight Center, Greenbelt, Md. "This is truly a
remarkable achievement!"

About 85 percent of the comets SOHO discovered belongs to
the Kreutz group of sun grazing comets, so named because
their orbits take them very close to Earth's star. The
Kreutz sun grazers pass within 500,000 miles of the
star's visible surface. Mercury, the planet closest to
the sun, is about 36 million miles from the solar surface.

SOHO has also been used to discover three other
well-populated comet groups: the Meyer, with at least 55
members; Marsden, with at least 21 members; and the Kracht,
with 24 members. These groups are named after the
astronomers who suggested the comets are related, because
they have similar orbits.

Many comet discoveries were made by amateurs using SOHO
images on the Internet. SOHO comet hunters come from all
over the world. The United States, United Kingdom, China,
Japan, Taiwan, Russia, Ukraine, France, Germany, and
Lithuania are among the many countries whose citizens
have used SOHO to chase comets.

Almost all of SOHO's comets are discovered using images
from its Large Angle and Spectrometric Coronagraph (LASCO)
instrument. LASCO is used to observe the faint,
multimillion-degree outer atmosphere of the sun, called
the corona. A disk in the instrument is used to make an
artificial eclipse, blocking direct light from the sun,
so the much fainter corona can be seen. Sun grazing
comets are discovered when they enter LASCO's field of
view as they pass close by the star.

"Building coronagraphs like LASCO is still more art
than science, because the light we are trying to detect
is very faint," said Dr. Joe Gurman, U.S. project
scientist for SOHO at Goddard. "Any imperfections in the
optics or dust in the instrument will scatter the light,
making the images too noisy to be useful. Discovering
almost 1,000 comets since SOHO's launch on December 2,
1995 is a testament to the skill of the LASCO team."

SOHO successfully completed its primary mission in April
1998. It has enough fuel to remain on station to keep
hunting comets for decades if the LASCO continues to
function.

For information about SOHO on the Internet, visit:

http://www.nasa.gov/vision/universe/solarsystem/1000comet.html

For information about NASA and agency programs on the
Internet, visit:

http://www.nasa.gov/home/index.html

-end-
Received on Wed 06 Jul 2005 02:19:22 PM PDT