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Jan.
14, 2008: Consider it a case of exquisite timing.
Just last week, solar physicists announced the beginning of
a new solar cycle and now, Jan. 14th, the Ulysses spacecraft
is flying over a key region of solar activity--the sun's North
Pole.
"This
is a wonderful opportunity to examine the sun's North Pole
at the onset of a new solar cycle," says Arik Posner,
NASA Ulysses program scientist. "We've never done this
before."
 Launched
in Oct. 1990 from the space shuttle Discovery, Ulysses is
a joint mission of the European Space Agency and NASA. Unlike
other spacecraft, Ulysses is able to fly over the sun's poles,
looking down on regions that are difficult to see from Earth:
diagram.
Right:
An artist's concept of the Ulysses spacecraft. Credit: ESA.
[more]
Ulysses
has flown over the sun's poles three times before in 1994-95,
2000-01 and 2007. Each flyby revealed something interesting
and mysterious, but this one may be most interesting of all.
"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," explains Ed Smith, Ulysses project scientist
at NASA's Jet Propulsion Laboratory.
Many
researchers believe the sun's poles are central to the ebb
and flow of the solar cycle. Consider the following: When
sunspots break up, their decaying magnetic fields are carried
toward the poles by vast currents of plasma. This makes the
poles a sort of "graveyard for sunspots." Old magnetic
fields sink beneath the polar surface two hundred thousand
kilometers deep, all the way down to the sun's inner magnetic
dynamo. There, dynamo action amplifies the fields for use
in future solar cycles.
One
big puzzle revealed by previous flybys is the temperature
of the sun's poles. In the previous solar cycle, the magnetic
north pole was about 80,000 degrees or 8% cooler than the
south. Why should there be a difference? No one knows.
The
current flyby may help solve the 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 vs. 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,"
says Smith.
Above:
A Ulysses "clock plot" of solar wind speed vs. latitude
reveals a high-speed wind blowing from the sun's poles. [more]
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 it is acting
a bit odd.
Posner
explains: "Eleven years ago, during a similar '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:
data."
Is
this a detail of little importance or a major anomaly, signaling
new things to come? Again, no one knows, and that's why now
is a good time to visit the sun's North Pole. "We'll
be monitoring the magnetic field above the north pole to see
what it's like during the change of solar cycles."
The
flyby is underway. Stay tuned to Science@NASA for results.
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Author: Dr.
Tony Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
| more
information |
|
Ulysses
home pages: NASA,
ESA.
Cool
Solar Mystery -- (Science@NASA) One pole of the
sun is cooler than the other. That's the surprising
conclusion announced by scientists who have been analyzing
data from the ESA-NASA Ulysses spacecraft.
Cold
Peril -- (Science@NASA) The NASA/ESA Ulysses spacecraft
is perilously cold as it begins a newly extended mission
to study the sun.
A
Star with two North Poles -- (Science@NASA) Ulysses
records an extraordinary upheaval in the sun's magnetic
field.
Solar
Flares on Steroids -- (Science@NASA) Solar flares
that scorch Earth's atmosphere are commonplace. But
scientists have discovered a few each year that are
not like the others: they come from stars thousands
of light years away. The Ulysses spacecraft is crucial
for pinpointing these "solar flares on steroids."
Solar
Spitwads -- (Science@NASA) Using data from the Ulysses
spacecraft, researchers have discovered that high-energy
particles from the Sun sometimes go in unexpected directions.
NASA's
Future: The
Vision for Space Exploration
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