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(meteorobs) [ASTRO] Ulysses Spacecraft Meets A Comet




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From: Ron Baalke <BAALKE@KELVIN.JPL.NASAdot gov>
Date: Wed, 5 Apr 2000 23:29:14 GMT
Subject: [ASTRO] Ulysses Spacecraft Meets A Comet

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasadot gov

Contact:  Jane Platt (818) 354-0880              

FOR IMMEDIATE RELEASE                         April 5, 2000

STRANGERS IN THE NIGHT: ULYSSES SPACECRAFT MEETS A COMET 

     During an unplanned rendezvous, the Ulysses spacecraft found 
itself gliding though the immense tail of Comet Hyakutake, 
revealing that comet tails may be much, much longer than 
previously believed. 

     "The odds that Ulysses' flight path would intersect the 
comet tail were probably less likely than someone breaking the 
bank at Monte Carlo," said Dr. Edward Smith of NASA' s Jet 
Propulsion Laboratory, Pasadena, CA, the Ulysses project 
scientist and a co-investigator for its magnetometer instrument. 
Before the unexpected encounter, Ulysses was hundreds of millions 
of kilometers, or miles, away from Comet Hyakutake and far beyond 
the visible tail.

     "This tail extends half a billion kilometers (more than 300 
million miles). That's more than three times the distance from 
the Earth to the Sun," said Dr. Nathan Schwadron, of the 
University of Michigan in Ann Arbor, a member of one of two 
Ulysses teams that made the discovery independently of one 
another. Findings from both teams appear in the April 6 issue of 
the journal Nature.

     "This makes it the longest comet tail ever recorded," said 
Dr. Geraint Jones from Imperial College, London, of the Ulysses 
magnetometer team. 

     Comet Hyakutake, one of the brightest comets of the 20th 
century, made a dazzling nighttime appearance in the spring of 
1996, when it made a close pass by the Sun. While Ulysses was 
cruising through space studying the solar wind on May 1, 1996, 
its data suddenly went wild for a few hours. For example, the 
solar wind seemed to almost disappear and was replaced by gases 
not normally found in the solar wind, and the magnetic field in 
the solar wind was distorted. Since Ulysses scientists were not 
looking for comets, they did not realize the significance of the 
data right away.

     "The discovery was made quite by accident, a bit like 
finding a needle in a haystack when you weren't even looking for 
a needle in the first place," said Dr. George Gloeckler of the 
University of Maryland, principal investigator of the Ulysses 
solar-wind ion-composition spectrometer team. The instrument 
studies the content and electrical charge of ionized gases. While 
his team detected ions typically found in comets, the 
magnetometer team observed magnetic field directional changes 
like those associated with comet tails.

     Comets are of great interest, because they may be the frozen 
leftovers of the birth of our solar system. They could hold clues 
to the formation of Earth and life, since one theory holds that 
comets "seeded" Earth and other planets with the building blocks 
of life. 

     Comets are made of dirty ice, and as they approach the Sun 
and heat up, they emit gas and dust, forming gas and dust tails. 
The gas slows the solar wind and the portion of the magnetic 
field near the comet. The parts of the magnetic field farther 
from the comet continue to travel rapidly past it. Magnetic 
fields can be stretched like rubber bands. The magnetic field is 
draped around the comet and stretches out behind it in a hairpin 
shape.

     Gloeckler is lead author of the Nature paper on the ion 
findings, along with Schwadron, and Drs. Lennard Fisk and Thomas 
Zurbuchen, also of the University of Michigan, and Dr. Johannes 
Geiss of the International Space Science Institute in 
Switzerland. The other Nature article, on the Ulysses 
magnetometer findings, was authored by Jones and Professor Andre 
Balogh of Imperial College and Dr. Timothy Horbury of Queen Mary 
and Westfield College, London.

     Jones at Imperial College looked more closely at the 
magnetic field data because of the publication of the unusual 
1996 solar wind event in the Journal of Geophysical Research. It 
was authored by Dr. Peter Riley, formerly of Los Alamos National 
Laboratory in New Mexico, and based on data from the Ulysses 
solar wind instrument. Jones and Horbury saw that the data looked 
like a cometary tail, and Jones searched until he found the 
tail's source -- Hyakutake. Gloeckler and his colleagues noticed 
the event independently and realized it was cometary material.

     Ulysses, launched in 1990, is a joint venture of NASA and 
the European Space Agency (ESA). The spacecraft studies the Sun 
from a high-latitude orbit, mostly at right angles to the plane 
of orbiting planets. Ulysses studies the Sun's magnetic fields, 
solar winds and cosmic rays near the Sun's North and South Poles, 
away from the equator, where Earth orbits. Ulysses has no camera, 
but its ten sophisticated instruments can observe some phenomena 
not detectable by visible observations. Scientists now know that 
sensitive instruments, like those found on Ulysses, can detect 
comet tail particles that are not normally visible. The Jet 
Propulsion Laboratory (JPL) manages Ulysses for NASA's Office of 
Space Science, Washington, D.C.

More information on the Ulysses mission is available at:  
http://ulysses.jpl.nasadot gov  and     
http://helio.estec.esadot nl/ulysses/

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NOTE:  Animation, interview clips and B-roll of the Ulysses comet 
encounter will air on NASA-TV at 3pm, 6pm and 9pm PDT today and 
again tomorrow at 9am, 12 noon, 3pm, 6pm and 9pm on NASA TV. NASA 
Television is available on transponder 9C of the GE-2 satellite 
at 85 degrees West longitude, vertical polarization, frequency 
3880 MHz, audio of 6.8 MHz.  

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