section_path: In outer space/Solar wind
section_name: Solar wind
paragraph_text: Solar wind
  
  Rather than air, the solar wind is a stream of charged particles —a plasma —ejected from the upper atmosphere of the Sun at a rate of 400 kilometers per second (890,000 mph). It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time. These particles are able to escape the Sun's gravity, in part because of the high temperature of the corona, but also because of high kinetic energy that particles gain through a process that is not well understood. The solar wind creates the Heliosphere, a vast bubble in the interstellar medium surrounding the Solar System. Planets require large magnetic fields in order to reduce the ionization of their upper atmosphere by the solar wind. Other phenomena caused by the solar wind include geomagnetic storms that can knock out power grids on Earth, the aurorae such as the Northern Lights, and the plasma tails of comets that always point away from the Sun.