Solar scientists know that understanding our star requires long-term study. So they're especially glad that a European-built solar probe named Ulysses, launched more than 16 years ago in October 1990, is once again positioned to explore the Sun's polar regions.
On February 7th, the craft reached its maximum solar latitude of –80°, midway through a five-month study of the southern pole. Ulysses will remain about 300 million km (200 million miles) from the Sun throughout the pass. Then, after sweeping up through the ecliptic plane next August, Ulysses will likewise study the Sun's northern polar region for five months beginning in November.
This will be Ulysses' third swing over the solar poles. After leaving Earth, the craft made a close flyby of Jupiter in February 1992 that redirected it back toward the Sun on a new, highly inclined, 6.2-year orbit. Its first polar sweep came in 1994–95, when the Sun was near the minimum of its 11-year activity cycle, and again in 2000–01, during the most recent solar maximum.
Among its many discoveries, Ulysses found that the solar wind, the Sun's continuous outflow of charged particles and entrained magnetic field lines, blows much faster and steadier at high solar latitudes. Since the Sun is again at minimum activity, mission scientists are particularly eager to see if solar-wind conditions match those found during the solar minimum in the 1990s.
After March 2008, mission managers may officially end Ulysses' mission due to dwindling electrical output from the craft's radioisotope-powered generators. The spacecraft is operated jointly by the European Space Agency and NASA. Its nine experiments continue to function, though they can no longer be powered up all together.