Solar Winds

The solar wind is a stream of electronically charged particles (plasma), which are ejected from the upper atmosphere of the sun. It consists mostly of high-energy electrons and protons (about 1 keV=1.6*10-19) that are able to escape the sun's gravity because of the high temperature of the corona and the high kinetic energy particles gain through a process that is not well understood at this time.

Many phenomenon are related to the solar wind, including geomagnetic storms capable of knocking out power grids on Earth, Northern Lights (e.g., Northern Lights) and the plasma tail of a comet always pointing away from the sun. While early models of the solar wind used primarily thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed solar wind. Some additional acceleration mechanism is required, but is not currently known, but most likely relates to magnetic fields in the solar atmosphere.

In the heliosphere, the composition of the solar wind is identical to the sun's corona: These components are present as a plasma, consisting of about 95% singly ionized hydrogen, 4% doubly ionized helium, and less than 0.5% other ions (often called minor ions). Carbon, nitrogen, oxygen, neon, magnesium, silicon and iron are the dominant minor ions. The exact composition has been routinely measured on Ulysses and ACE, two spacecraft carrying a Solar Wind Ion Composition Spectrometer. Unexpectedly, the solar wind composition shows substantial variation, likely directly reflecting the physics of the underlying corona. The first detailed composition measurements were performed by Geiss on the moon, which was part of the first Moon-landing. Solar wind was collected using a specially prepared metal-foil and then brought back for analysis. A similar technique was recently pursued using a robotic approach: A sample return mission, Genesis, returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on re-entry to Earth's atmosphere, possibly contaminating the solar samples.

Near Earth, the velocity of the solar wind varies from 200 to 889 km/s. The average is 450 km/s. Approximately 1~{!A~}109 kg/s of material is lost by the Sun as ejected solar wind, about one-fifth that lost due to fusion, which is equivalent to about 4.5 Tg (4.5~{!A~}109 kg) of mass converted to energy every