Ulysses makes a return trip

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.