Ulysses, a joint mission by NASA and the European Space Agency (ESA) to study the Sun's environment and the solar wind, was launched in October 1990. This was the first time a spacecraft had been deliberately sent out of the ecliptic (the plane of the Solar System). After receiving a gravity assist from Jupiter in February 1992, the Ulysses probe went on to pass over the Sun's south pole in May 1994, then over its north pole a year later.
As well as gathering data about the solar wind, Ulysses' instruments have returned important information about the interplanetary magnetic field, interplanetary dust, and cosmic rays.
The Japanese have sent two solar observatories designed to study extremes of solar energy. Hintori ("firebird"), launched in 1981, collected X-ray data on the 11-year cycle of solar activity. Yohkoh ("sunbeam"), launched in 1991, carries X-ray and ultraviolet telescopes to image the Sun's rarefied corona and to study solar flares.
The Solar Heliospheric Observatory (SOHO) was launched in December 1996. A joint project of the ESA and NASA, SOHO was placed into orbit around a Lagrangian point—a region about 930,000 miles (1.5 million km) sunward from Earth where the gravitational pull of the Sun and Earth are in balance. SOHO's instruments are studying the temperature and structure of the Sun's interior, the corona, and the solar wind, and how these change as the Sun becomes more active.