The Sun’s outer atmosphere, the super-hot corona, is the source of the solar wind, a steady outflow of charged particles from the Sun. These particles have gained enough energy to fill the heliosphere, a region of space that extends well past the orbit of Pluto. As these particles flow past Earth’s orbit, they’re traveling at an average of 400 kilometers per second. Though the Sun can lose more than a million tons of material each second, the amount is still negligible compared to the Sun’s total mass.
The solar wind is primarily composed of roughly equal numbers of protons and electrons, as well as a few heavier ions. The particles’ velocities are highest over coronal holes, areas near the Sun’s poles associated with “open” magnetic field lines that allow material to flow more easily into space. Particles flow out more slowly near the Sun’s equator, where magnetic field lines loop back on themselves and trap coronal material.
Earth’s magnetic field protects our planet, carving out a cavity in the solar wind called the magnetosphere. Because of the solar wind’s pressure on the magnetic field, the magnetosphere is compressed on the Sun-facing side. On the opposite side, it stretches out into a magnetotail.
Occasionally, the Sun’s charged particles find their way into Earth’s magnetosphere, and spiral along magnetic field lines toward the poles, where they interact with particles in the Earth’s upper atmosphere to create auroras.