The solar wind is a stream of charged particles emitted by the sun. The solar wind is primarily protons (hydrogen ions), but also has some components of higher mass, including deuterium and helium, as well as electrons. The solar wind has a density of a few particles per cubic centimeter, and moves at a speed of a bit over a million km/hr. Both the density and the speed of the solar wind change with the activity of the sun.
The solar wind is deflected by magnetic fields, and hence does not directly impact the Earth's surface or atmosphere. Lacking a magnetic field, the moon is directly exposed to the solar wind, and hence solar wind elements can be found implanted into Lunar regolith. Hydrogen implanted into the Lunar Soil might be a resource for lunar In Situ Resource Utilization (see Volatiles, and Helium 3 from the solar wind has been proposed as possible fusion fuel.
One proposed method of space propulsion is to sail on the solar wind using a "magnetic sail" ("Magsail") or a "Mini-magnetosphere Plasma Propulsion" ("M2P2") sail.
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