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Solar Wind Basics      Solar wind is the outward flow of solar particles. Parker developed a theory of the solar wind in the 1950's. He said that solar wind must exist because the gravitational force on particles in the outermost layer of the sun was not great enough to balance the pressure force. Because of this the particles must flow outward from the sun. A pressure force is directed from high to low pressure. The sun's corona has a higher pressure than interplanetary space so the pressure force points away from the sun. The sun has a larger mass than the mass of the individual particles so the gravitation force points towards the sun. Since the force of gravity towards the sun is less than the pressure force away from the sun, the particles move away from the sun. Parker further supported his theory by modelling a supersonic solar wind. Konstantin Gringawz in 1960-1961 used the Soviet spacecraft, Lunkik 2, and confirmed the presence of high-speed ions in interplanetary space. Right after Gringawz's discovery Herbert Bridge figured out the speed, density, and direction of solar wind. He used data from the American spacecraft Explorer 10 to help him discover this. Following Bridge's discovery Neugebauer & Snyder used data from the spacecraft, Mariner II, and found high-speed solar wind streams. To learn more about solar wind check out our various solar wind topics on the left.