Wind as the Earth to evolve into planets like Venus. Additionally, planets with hotter lower atmospheres could accelerate the loss rate of hydrogen. 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 . 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
Cosmic microwave background was denser, much hotter, and filled with a uniform glow from a white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, protons and electrons combined to form neutral hydrogen atoms. Unlike the uncombined protons and electrons, these newly conceived atoms could not absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog. Cosmologists refer to the time period when neutral atoms first formed as the "recombination epoch", and the event shortly afterwards when photons started to travel freely through