Solar Wind

One of the mysteries of the Sun is that its atmosphere becomes hotter at larger heights from its visible surface, or photosphere. While the photosphere has a temperature of 9,981°F (5,527°C), the chromosphere, only a few thousand kilometers higher, is more than twice as hot. Further out is the corona, with gas heated to one or two million degrees Kelvin.

Although the reasons for this temperature rise are not well understood, the effects on the particles comprising the gas are known. The hotter a gas is, the faster its particles move. In the corona, the free protons and electrons move so rapidly that the Sun's gravity cannot hold them, and they escape entirely, flowing into the solar system. This stream of particles is called the solar wind.

The solar wind is made mainly of free protons and electrons. These particles are much lighter than the atoms (such as iron) in the solar corona, so the Sun has a weaker hold on them than on their heavier counterparts. When the solar wind reaches Earth, the protons and electrons are flowing along at speeds up to 621 mi/s (1,000 km/s). By comparison, a commercial jet might fly 621 MPH (1,000 km/hr), and only if it has a good tailwind pushing it along. The solar wind could flow from New York to Los Angeles in less than ten seconds.

There is, therefore, gas from the Sun literally filling the solar system. We cannot see it, however, because there is not much of it—only a few protons and electrons per cubic centimeter. The solar wind therefore represents an insignificant source of mass loss for the Sun, not nearly enough to have any impact on its structure or evolution. (Some very massive stars do have strong winds that affect how they evolve.)