Hinode Reveals New Insights About the Origin of Solar Wind

Dec. 6, 2007

Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@xxxxxxxx

Jennifer Morcone
Marshall Space Flight Center, Huntsville, Ala.
256- 544-7199
jennifer.j.morcone@xxxxxxxx

RELEASE: 07-264

SPACECRAFT REVEALS NEW INSIGHTS ABOUT THE ORIGIN OF SOLAR WIND

WASHINGTON - Images from NASA-funded telescopes aboard a Japanese
satellite have shed new light about the sun's magnetic field and the
origins of solar wind, which disrupts power grids, satellites and
communications on Earth.

Data from the Hinode satellite shows that magnetic waves play a
critical role in driving the solar wind into space. The solar wind is
a stream of electrically charged gas that is propelled away from the
sun in all directions at speeds of almost 1 million miles per hour.
Better understanding of the solar wind may lead to more accurate
prediction of damaging radiation waves before they reach satellites.
Findings by American-led international teams of researchers appear in
the Dec. 7 issue of the journal SCIENCE.

How the solar wind is formed and powered has been the subject of
debate for decades. Powerful magnetic Alfv?n waves in the
electrically charged gas near the sun have always been a leading
candidate as a force in the formation of solar wind since Alfv?n
waves in principle can transfer energy from the sun's surface up
through its atmosphere, or corona, into the solar wind.

In the solar atmosphere, Alfv?n waves are created when convective
motions and sound waves push magnetic fields around, or when dynamic
processes create electrical currents that allow the magnetic fields
to change shape or reconnect.

"Until now, Alfv?n waves have been impossible to observe because of
limited resolution of available instruments," said Alexei Pevtsov,
Hinode program scientist, NASA Headquarters, Washington. "With the
help of Hinode, we are now able to see direct evidence of Alfv?n
waves, which will help us unravel the mystery of how the solar wind
is powered."

Using Hinode's high resolution X-ray telescope, a team led by
Jonathan
Cirtain, a solar physicist at NASA's Marshall Space Flight Center,
Huntsville, Ala., was able to peer low into the corona at the sun's
poles and observe record numbers of X-ray jets. The jets are
fountains of rapidly moving hot plasma. Previous research detected
only a few jets daily.

With Hinode's higher sensitivity, Cirtain's team observed an average
of 240 jets per day. They conclude that magnetic reconnection, a
process where two oppositely charged magnetic fields collide and
release energy, is frequently occurring in the low solar corona. This
interaction forms both Alfv?n waves and the burst of energized plasma
in X-ray jets.

"These observations show a clear relationship between magnetic
reconnection and Alfv?n wave formation in the X-ray jets." said
Cirtain. "The large number of jets, coupled with the high speeds of
the outflowing plasma, lends further credence to the idea that X-ray
jets are a driving force in the creation of the fast solar wind."

Another research team led by Bart De Pontieu, a solar physicist at
Lockheed Martin's Solar and Astrophysics Laboratory, Palo Alto,
Calif., focused on the sun's chromosphere, the region sandwiched
between the solar surface and its corona. Using extremely
high-resolution images from Hinode's Solar Optical Telescope, De
Pontieu's team found that the chromosphere is riddled with Alfv?n
waves. When the waves leak into the corona, they are strong enough to
power the solar wind.

"We find that most of these Alfv?n waves have periods of several
minutes, much longer than many theoretical models have assumed in the
past," says De Pontieu. Comparisons with advanced computer
simulations from the University of Oslo, Norway, indicate that
reconnection is not the only source of the Alfv?n waves. "The
simulations imply that many of the waves occur when the sun's
magnetic field is jostled around by convective motions and sound
waves in the low atmosphere," continued De Pontieu.

Hinode was launched in September 2006 to study the sun's magnetic
field and how its explosive energy propagates through the different
layers of the solar atmosphere. It is a collaborative mission with
NASA and the space agencies of Japan, the United Kingdom, Norway and
Europe and Japan's National Astronomical Observatory. Marshall
manages science operations and managed the development of the
scientific instrumentation provided for the mission by NASA, industry
and other federal agencies. The Lockheed Martin Advanced Technology
Center, Palo Alto, Calif., is the lead U.S. investigator for the
Solar Optical Telescope. The Smithsonian Astrophysical Observatory,
Cambridge, Mass. is the lead U.S. investigator for the X-Ray
Telescope.

To view images about these findings and learn more about Hinode,
visit:

http://www.nasa.gov/solar-b


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