From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Jupiter's Magnetic Field Shaped by Solar Wind
News-Software: VAX/VMS VNEWS 1.3-4   
Keywords:  Jupiter, Ulysses, JPL, ESA
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Sat, 12 Sep 1992 04:43:04 GMT

Michael Braukus
Headquarters, Washington, D.C.                       September 11, 1992
(Phone:  202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)

RELEASE:  92-145

JUPITER'S MAGNETIC FIELD SHAPED BY SOLAR WIND

	Scientists studying data from Jupiter's highly charged magnetic
environment -- acquired by the Ulysses spacecraft encounter in February
1992 -- reported in a series of papers published today that the solar wind
exerts a much stronger influence on the planet's magnetic field than
previously thought.

	The discovery was the result of Ulysses' unique trajectory, which took
the spacecraft to higher latitudes near the planet than were reached by
previous spacecraft, said JPL Ulysses Project Scientist Dr. Edward J. Smith,
principal author of one of seven articles published today in Science magazine.

	"In addition, Ulysses' outbound path took the spacecraft through
another previously unexplored region in the dusk sector, where we had never
been before," Smith said.

	Three separate findings during the Jupiter encounter supported this
conclusion, Smith said.  The first evidence was derived from Ulysses' flight
through the high latitude region of  the magnetic field -- called the
magnetosphere -- in which the planetary magnetic field lines led out into
interplanetary space rather than returning to Jupiter across the equator.

	 "Five of the experiments sensed this transition simultaneously, once
at a distance of only 7 planetary radii (500,000 miles) and a second time at a
distance of 15 radii (1.1 million miles)," Smith said.

	The second major surprise occurred as the spacecraft was traveling
outbound.  Measurements showed that the magnetic field was not rotating
with the planet but was being swept downstream toward the magnetic tail of
the magnetosphere, Smith said.

	"This property was seen well inside the magnetosphere at large
distances from the boundary with the solar wind," Smith said.  "It is,
nevertheless, attributed by scientists to a dragging effect of the solar wind
on the magnetosphere."

	The third piece of the puzzle leading the Ulysses teams to this
conclusion was the identification of a thick layer just inside the boundary of
the magnetosphere in which solar wind particles and Jovian particles appear
to be intermingling, and the magnetic field is not rotating with the planet.

	"Scientists interpreted these observations to imply that magnetic field
lines are being peeled away from the magnetosphere by the solar wind,"
Smith said.

	Jupiter's magnetic field, the largest in the solar system, forms a
windsock -- the magnetosphere -- that is blown by the solar wind.  The
magnetosphere is known to vary in size and configuration over time
depending on the amount of force exerted on it by the solar wind.  Millions of
highly charged particles swirl and bounce around within this magnetic bubble
and many of them eventually escape into interplanetary space.

	Smith published his findings along with Dr. Edgar Page, European
Space Agency (ESA) science coordinator, and ESA Project Manager Dr. Klaus-
Peter Wenzel.  Other results of Ulysses' milestone flight past Jupiter were
reported in subsequent articles.

	"Jupiter is like a cosmic-ray source spewing these things out into
interplanetary space all the time," said co-author Page. "The energy probably
comes from the planet's rapid rotation every 10 hours."  Smith said scientists
have made similar observations of the effects of the solar wind on Earth's
magnetosphere.

	"At Earth, magnetic fields at high latitudes lead out into space,
magnetic fields on the flanks of the magnetosphere are pulled tailward and a
boundary layer exists adjacent to the solar wind flowing around the
magnetosphere," he said.

	"For many years, theorists have believed that the solar wind was
exerting much less influence on the giant, strongly magnetized Jupiter than
on the smaller magnetosphere of Earth," Smith said.  "The latest results do
not mean that Jupiter is like the Earth in all aspects, but theorists aware of
the new Ulysses results are now revising their ideas."

	Ulysses is a joint NASA-ESA mission to study the poles of the sun and
will begin its primary mission in June 1994.
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    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
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