Outer Space Outer space , commonly shortened to space , is the expanse that exists beyond Earth and its atmosphere and between celestial bodies . Outer space is not completely empty; it is a near-perfect vacuum [1] containing a low density of particles, predominantly a plasma of hydrogen and helium , as well as electromagnetic radiation , magnetic fields , neutrinos , dust , and cosmic rays . The baseline temperature of outer space, as set by the background radiation from the Big Bang , is 2.7 kelvins (−270 °C ; −455 °F ). [2] The plasma between galaxies is thought to account for about half of the baryonic (ordinary) matter in the universe, having a number density of less than one hydrogen atom per cubic metre and a kinetic temperature ...