[meteorite-list] Ulysses Spacecraft Data Reveal a Comet Biggie

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 14 Apr 2010 15:17:46 -0700 (PDT)
Message-ID: <201004142217.o3EMHkAc010325_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-127

Ulysses Spacecraft Data Reveal a Comet Biggie
Jet Propulsion Laboratory
April 13, 2010

PASADENA, Calif. - Using data from the completed ESA/NASA Ulysses
mission, scientists have identified a new candidate for biggest comet.
Results of these findings were presented today at the Royal Astronomical
Society's National Astronomy Meeting in Glasgow by Ulysses science team
member Geriant Jones of University College, London

The primary mission of the Ulysses spacecraft was to characterize the
sun's heliosphere as a function of solar latitude. The heliosphere is
the vast region of interplanetary space occupied by the sun's atmosphere
and dominated by the outflow of the solar wind. To study the
heliosphere, Ulysses was placed into a six-year orbit around the sun
that carried it out to Jupiter's orbit and back. Covering such a vast
expanse of space provided unique and unexpected opportunities for the
spacecraft. During its more than 17-year mission, Ulysses had three
unplanned encounters with comet tails. (See Ulysses Catches Record for
Catching Comets by Their Tails -
http://www.nasa.gov/vision/universe/solarsystem/ulysses-20071019.html )

Scientists combed the data of a chance 2007 encounter Ulysses made with
the tail of comet McNaught. The nucleus of this comet was some 257
million kilometers (160 million miles) from the spacecraft during
encounter. Instead of using the length of the tail to measure the scale
of the comet, scientists used Ulysses data to gauge the size of the
region of space disturbed by the comet's presence. Ulysses' solar wind
ion composition spectrometer instrument, developed by University of
Michigan heliophysicist George Gloeckler, found that even at such a
great distance, the tail had filled the solar outflow with unusual gases
and molecules. In response, the solar wind that usually measures about
700 kilometers per second (435 miles per second) at that distance from
the sun, was less than 400 kilometers per second (249 miles per second)
inside the comet's tail, as measured by one of Ulysses' instruments
called "Solar Wind Observations Over the Poles of the Sun," whose
principal investigator is Dave McComas of the Southwest Research
Institute in San Antonio, Texas.

Ulysses took nearly nine times as long to traverse the tail of comet
McNaught in 2007 as it did during a 1996 chance encounter with comet
Hyakutake - which until now held the record for longest known tail. This
led scientists to believe the comet McNaught was remarkably productive
in releasing gas and material from its surface. While measuring such
comet "outgassing" can define the level of activity of a comet, it does
not directly relate to its size. But if both comets were equally active,
McNaught would have to be much larger in size to produce such a massive
tail.

The interaction between comets' tails and the solar wind has been
studied for decades. A comet's ion tail always points away from the sun,
whether the body is traveling toward or away from the sun along the
comet's elliptical orbit. It was this finding that eventually led in
1958 to the discovery of solar wind. The magnetism and velocity of the
solar wind are so strong, the effect pushes the comet's tail outward.

When space shuttle Discovery launched Ulysses on Oct. 6, 1990, it had an
expected lifetime of five years. The mission gathered unique information
about the heliosphere, the bubble in space carved by the solar wind, for
nearly four times longer than expected. The mission ended on June 30, 2009.

The Ulysses spacecraft was built by Dornier Systems of Germany for ESA.
NASA provided the launch and the upper stage boosters. The U.S.
Department of Energy, Washington, supplied the generator that powers the
spacecraft; science instruments were provided by both U.S. and European
investigators. The spacecraft was operated from JPL by a joint NASA/ESA
team and employed NASA's Deep Space Network for communications.

The Royal Astronomical Society's press release on the finding is online
at: http://www.astro.gla.ac.uk/nam2010/pr8.php .

More information about NASA's Ulysses mission is available at:
http://ulysses.jpl.nasa.gov.

D.C. Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle at jpl.nasa.gov

2010-127
Received on Wed 14 Apr 2010 06:17:46 PM PDT