A spacecraft in solar orbit reached almost directly above
the south pole of the Sun last week, giving
scientists a rare glimpse of this unfamiliar territory.
Launched on
October 6, 1990, Ulysses, a joint mission of NASA and the European Space Agency, has
made only two flybys of the south pole of the Sun.
"The
sun's south pole is uncharted territory," said Ulysses Program Scientist Arik
Posner of NASA headquarters. "We can barely see it from Earth, and most of
our sun-studying spacecraft are stationed over the sun's equator with a poor
view of higher latitudes."
The
duration of the spacecraft's south polar pass is roughly four months. Last
Thursday was the day of Ulysses' closest approach to that solar region.
The
spacecraft hasn't spent enough time at the sun's high latitudes to really take
in all the solar secrets that can be revealed from that point of view, Posner
said. "We are trying to get all the information that we can get from these
flybys," he said.
For more
than 15 years, Ulysses has been collecting data that has led to a better understanding of the Sun's
environment, which could also help scientists understand Earth better.
"Both
the sun's and Earth's
magnetic poles are constantly on the move, and they occasionally do a
complete flip,
with N and S changing places," Posner said.
This
flipping happens every
11 years on the Sun, in synch with the sunspot
cycle. It happens every 300,000 years or so on Earth, but no one knows what
the Earth's cycle corresponds with.
"Studying
the polar magnetic field of the sun might give us some clues about the magnetic
field of our own planet," Posner said.
Ulysses is
also collecting data on the holes over the sun's poles, known as coronal holes.
These are regions where the magnetic field of the Sun opens, allowing solar
winds to escape and galactic cosmic rays to get in.
"Flying
over the sun's poles, you get slapped in the face by a hot, million mph stream
of protons and electrons," Posner said.
The last
flyby of the Sun's South Pole, prior to this year's, took place in 2000-2001. Scientists
are now eagerly waiting to examine the data from latest flyby.
"The
interesting thing about the past flybys was that, especially the ones in the solar
minimum, there were some asymmetries between the north and the south [poles], and
we are now trying to learn whether these are still there or whether they have
changed," Posner told SPACE.com. "That is what we are eagerly awaiting."
Ulysses' next
and probably last solar flyby of will be of the Sun's North Pole in the spring
of 2008. The spacecraft will most likely be abandoned in a cosmic junkyard soon
thereafter when its internal power sources fail.
"We'll have
to see whether it's possible to extend it beyond that point," Posner said.
"This will be a question that will come up after we have the North Pole flyby.
After that, the next flyby will be in 6 years, but realistically I don't think
we can make that."
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