A common mission of NASA and the European Space Agency launched on Oct. 6, 1990. It was a spacecraft named Ulysses sent in solar orbit but the vehicle has accomplished by now only two flybys on the south pole of the star.

Last week, the spacecraft offered new pictures of this unexplored zone. "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."

Ulysses will stay in the area for about four months. "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.

The data transmitted by Ulysses for 16 years offers not only an understanding of the Sun's environment, but also of the Earth's. "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 shift occurs each 11 years on the Sun, in connection with the sunspot cycle. On the Earth, this occurs at roughly 300,000 years, but scientists do not know to what it is linked. "Studying the polar magnetic field of the sun might give us some clues about the magnetic field of our own planet," Posner said.

Ulysses offered also data on the coronal holes, situated over the Sun's poles, points where Sun's magnetic field is interrupted, permitting solar winds to get out and 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 previous flyby of the Sun's south pole occurred in 2000-2001. "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," said Posner.

Ulysses' next solar flyby will investigate the star's north pole in the spring of 2008. This could be its last mission, as the spacecraft will be discarded in a cosmic junkyard when its internal power sources are depleted. "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."

Photo credit: ESA