Part of a comet's streaming tail is plasma from gas ionized by sunlight and other unknown processes.
The Sun is a 1.5-millionkilometer ball of plasma. It is heated by nuclear fusion.
Scientists study plasma for practical purposes.
In an effort to harness fusion energy on Earth, physicists are studying devices that create and confine very hot plasmas in magnetic fields.
In space, plasma processes are largely responsible for shielding Earth from cosmic radiation, and much of the Sun's influence on Earth occurs by energy transfer through the ionized layers of the upper atmosphere.