SOLAR WIND

flux of particles, chiefly protons and electrons together with nuclei of heavier elements in smaller numbers, that are accelerated by the high temperatures of the solar corona, or outer region of the Sun, to velocities large enough to allow them to escape from the Sun's gravitational field. The solar wind is responsible for deflecting both the tail of the Earth's magnetosphere and the tails of comets away from the Sun. At a distance of one astronomical unit (the mean distance between the Earth and the Sun, or about 150,000,000 km), during a relatively quiet period, the wind contains approximately 1 to 10 protons per cubic centimetre moving outward from the Sun at velocities of 350 to 700 km (about 220 to 440 miles) per second; this creates a positive ion flux of 108 to 109 ions per square centimetre per second, each ion having an energy equal to at least 15 electron volts. During solar flares, the proton velocity, flux, plasma temperature, and associated turbulence increase substantially. When the solar wind encounters the Earth's magnetic field, a shock wave results, the nature of which is not fully understood. The portion of the solar wind that does not interact with the Earth or the other planets continues to travel to a distance of approximately 20 astronomical units, at which point it cools and eventually diffuses into galactic space.