Uncharted Territory: New Glimpse of the Sun's South Pole

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.

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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.

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 "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."

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 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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