Stellar Wind

The outermost layer of the sun is the corona, which is a very hot tenuous gas visible only during a solar eclipse. Because the coronal temperatures are typically one or two million degrees Kelvin, the individual atoms are ionized and moving very rapidly. The fastest ions are moving faster than the sun's escape velocity. So they escape, forming the solar wind.

Near Earth's orbit, the solar wind particles rush by at speeds of roughly 248-310 mi per second (400-500 km per second). There is considerable variation in the speed because the solar wind is gusty. The solar wind density is also variable, but typically runs to a few particles per cubic centimeter. The solar wind extends well beyond the orbit of Pluto to roughly 100 astronomical units (100 times the earth to sun distance). At this point, called the heliopause, the solar wind merges into the interstellar gas and dust.