Ulysses Spacecraft Flies Over Sun's North Pole

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Dwayne Brown 202-358-1726
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NEWS RELEASE: 2008-004 Jan. 14, 2008

Ulysses Spacecraft Flies Over Sun's North Pole

The Ulysses spacecraft today is making a rare flyby of the sun's north pole. Unlike any other
spacecraft, Ulysses is able to sample winds at the sun's poles, which are difficult to study from
Earth.
Ulysses has flown over the sun's poles three times before, in 1994-95, 2000-01 and 2007. Last
week, solar physicists announced the first indications of a new solar cycle. Visiting the pole at
this time may lead to new insights about solar activity.

"This is a wonderful opportunity to examine the sun's north pole within a transition of cycles,"
said Arik Posner, Ulysses program scientist at NASA Headquarters in Washington. "We've
never done this before."

Many researchers believe the sun's poles are central to the 11-year ebb and flow of solar
activity. When sunspots break up, their decaying magnetic fields are carried poleward by vast
currents of plasma. This makes the poles a sort of graveyard for sunspots. Old magnetic fields
sink beneath the polar surface 200,000 kilometers deep (about 124,000 miles), all the way
down to the sun's inner magnetic dynamo, which generates the solar magnetic field. There,
dynamo action amplifies the fields for use in future solar cycles.

"Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be
crucial to studies of the solar cycle," said Ed Smith, Ulysses project scientist at NASA's Jet
Propulsion Laboratory, Pasadena, Calif.

Each previous flyby revealed something interesting and mysterious. One puzzle has been the
temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about
80,000 degrees Fahrenheit (more than 44,000 degrees Celsius), or 8 percent cooler than the
south. The current flyby may help solve this puzzle because it comes less than a year after a
similar south pole flyby in Feb. 2007. Mission scientists will be able to compare temperature
measurements, north versus south, with hardly any gap between them.

Ulysses also discovered the sun's high-speed polar wind. At the sun's poles, the magnetic field
opens up and allows solar atmosphere to stream out at a million miles per hour. By flying
around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been
able to monitor this polar wind throughout the solar cycle and has found that it is acting a bit
odd.

"Twelve years ago, just before the previous 'sea change' between solar cycles, the polar wind
spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is
bottled up, confined to latitudes above 45 degrees, " said Posner.

Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of NASA
and the European Space Agency.

For more information about Ulysses, visit http://Ulysses.jpl.nasa.gov .

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