Solar wind
The stream of charged particles blowing continuously out from the Sun. It fills the solar system at several hundred kilometres per second.
In 1958 Eugene Parker calculated that the Sun's hot outer atmosphere, the corona, cannot be held back by gravity and must flow outward continuously at supersonic speed[1]. The idea met strong resistance at the time, but in 1962 Mariner 2, on its way to Venus, measured an unbroken stream of particles directly and confirmed it[2].
The solar wind strikes Earth's magnetic field and produces the aurora; when strong, it disrupts satellites and power grids. Spacecraft stationed at the Lagrange point between the Sun and Earth therefore watch the solar wind about an hour before it arrives. The limit of its reach is the heliopause, which Voyager 1 crossed in 2012.
Related terms
- HeliopauseThe boundary where the flow of particles from the Sun (the solar wind) is stopped by the gas between the stars — one definition of the outer edge of the solar system.
- Van Allen beltDoughnut-shaped regions where high-energy protons and electrons are trapped by Earth's magnetic field. There is an inner and an outer belt.
- Lagrange pointFive points where the gravity of two bodies, such as the Sun and Earth, balances the motion of orbiting around them, so a small object can hold its position.