By Ron Cowen
Just as the sun is reaching the stormy peak of its 11-year activity cycle, the European Space Agency’s Ulysses spacecraft has begun its second pass over the sun’s poles. Six years ago, when Ulysses completed its first polar swoop, the sun was at the minimum of its cycle and relatively quiescent.
Back then, Ulysses’ measurements revealed that the solar wind—the stream of charged particles flowing out of the sun—was blowing at a rapid, steady rate of 750 kilometers per second at the poles. Today the solar wind at the same high latitudes is more chaotic and blustery.
Ulysses crossed the solar latitude of 70ºS on Sept. 8 and will spend the next 4 months flying over the sun’s south polar region. Then, after swinging back over the sun’s equator, the craft will begin passing over the sun’s northern polar area on Sept. 3, 2001. Ulysses is scheduled to complete its second and final trip around the sun in 2004.
“By the time the mission comes to an end, Ulysses will have gathered the only set of observations above the solar poles covering more than a complete 11-year solar cycle,” says Ulysses scientist André Balogh of the Imperial College of Science, Technology, and Medicine in London.
