The Sun's outer layers form the corona, and are heated to millions of degrees by a continual input of energy from the surface, where magnetic fields twist and reconnect. In a hail of millions of solar micro-flares per day, magnetic energy from these constant 'short circuits' is pumped into accelerating protons and electrons to high energy, and these then diffuse into the corona to heat it. The solar wind consists os the flow of particles from the Sun at speeds of 300-400 kilometers/sec. By the time this wind reaches the orbit of the Earth, its density is only about 5 particles ( mostly hydrogen and helium nuclei) per cubic centimeter. The Sun loses about 1/100 trillionth of its mass every year from this wind. Other stars have much heftier winds that cause the star to lose 1/100,000 of its mass each year.
High-speed wind streams arise from coronal holes. These are regions in the corona where the magnetic field of the Sun opens out into interplanetary space, but does not return to the surface of the Sun. Particles from the surface flow out along these magnetic pipes...which can cover 10-20 percent of the solar surface or more, and enter interplanetary space at speeds of a thousand km/sec. There are also eruptions of matter called coronal mass ejections that occur almost weekly, and these expel billions of tons of matter in a few hours. All of these things together, produce a net outflow of particles from the solar surface, and blend together into a wind that flows through the solar system, beyond the orbit of Pluto, and on into interstellar space.
All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY project.