interplanetary magnetic field
- The magnetic field of the solar system, arising from the magnetic activity of the Sun and strongly affecting the flow of particles in the solar wind. For many years most knowledge of this magnetic field came from observations made in the plane of the Earth’s orbit, from satellites in Earth orbit. But in the 1990s the Ulysses mission provided detailed measurements of the solar wind and solar magnetism deep into the solar system and high above the plane of the ecliptic. Here the main influence is the field around the Sun’s polar region rather than that at its equator.