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Date: Tue, 23 Sep 2008 10:12:56 -0700
From: NASA Jet Propulsion Laboratory <>
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Subject: Ulysses Reveals Global Solar Wind Plasma Output at 50-Year Low


DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown 202-358-1726
NASA Headquarters, Washington

September 23, 2008

Ulysses Reveals Global Solar Wind Plasma Output at 50-Year Low

PASADENA, Calif. -- Data from the Ulysses spacecraft, a joint
NASA-European Space Agency mission, show the sun has reduced its output
of solar wind to the lowest levels since accurate readings became
available. The sun's current state could reduce the natural shielding
that envelops our solar system.

"The sun's million mile-per-hour solar wind inflates a protective bubble,
or heliosphere, around the solar system. It influences how things work
here on Earth and even out at the boundary of our solar system where it
meets the galaxy," said Dave McComas, Ulysses' solar wind instrument
principal investigator and senior executive director at the Southwest
Research Institute in San Antonio, Texas. "Ulysses data indicate the
solar wind's global pressure is the lowest we have seen since the
beginning of the space age."

The sun's solar wind plasma is a stream of charged particles ejected from
the sun's upper atmosphere. The solar wind interacts with every planet in
our solar system. It also defines the border between our solar system and
interstellar space.

This border, called the heliopause, is a bubble-shaped boundary
surrounding our solar system where the solar wind's strength is no longer
great enough to push back the wind of other stars. The region around the
heliopause also acts as a shield for our solar system,
warding off a significant portion of the cosmic rays outside the galaxy.

"Galactic cosmic rays carry with them radiation from other parts of our
galaxy," said Ed Smith, NASA's Ulysses project scientist at the Jet
Propulsion Laboratory in Pasadena, Calif. "With the solar wind at an
all-time low, there is an excellent chance the heliosphere will diminish
in size and strength. If that occurs, more galactic cosmic rays will make
it into the inner part of our solar system."

Galactic cosmic rays are of great interest to NASA. Cosmic rays are
linked to engineering decisions for unmanned interplanetary spacecraft
and exposure limits for astronauts traveling beyond low-Earth orbit.

In 2007, Ulysses made its third rapid scan of the solar wind and magnetic
field from the sun's south to north pole. When the results were compared
with observations from the previous solar cycle, the strength of the
solar wind pressure and the magnetic field embedded in the solar wind
were found to have decreased by 20 percent. The field strength near the
spacecraft has decreased by 36 percent.

"The sun cycles between periods of great activity and lesser activity,"
Smith said. "Right now, we are in a period of minimal activity that has
stretched on longer than anyone anticipated."

Ulysses was the first mission to survey the space environment over the
sun's poles. Data Ulysses has returned have forever changed the way
scientists view our star and its effects. The venerable spacecraft has
lasted more than 17 years, or almost four times its expected mission
lifetime. The Ulysses solar wind findings were published in a recent
edition of Geophysical Research Letters.

The Ulysses spacecraft was carried into Earth orbit aboard space shuttle
Discovery on Oct. 6, 1990. From Earth orbit it was propelled toward
Jupiter, passing the planet on Feb. 8, 1992. Jupiter's immense gravity
bent the spacecraft's flight path downward and away from the plane of the
planets' orbits. This placed Ulysses into a final orbit around the
sun that would take it over its north and south poles.

The Ulysses spacecraft was provided by ESA, having been built by Astrium
GmbH (formerly Dornier Systems) of Friedrichshafen, Germany. NASA
provided the launch vehicle and the upper stage boosters. The U.S.
Department of Energy supplied a radioisotope thermoelectric generator to
power the spacecraft. Science instruments were provided by U.S. and
European investigators. The spacecraft is operated from JPL by a joint
NASA-ESA team.

More information about the Ulysses mission is available
at .


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