Space science covers everything from Earth's surface to the Sun and then out into the galaxy. The range of space physics studied here is from Earth's ionosphere to the Sun's surface to the outer boundaries of the heliosphere and solar system, where the Sun's "solar wind" interacts with the local interstellar medium. As such it includes the solar corona and solar wind (sometimes called the interplanetary medium), the ionospheres and magnetospheres of Earth and the other planets, and the "Space Weather" that results from interactions between the Sun and Earth.
Space physics is essential for understanding humanity's local environment and solar system. It is also crucial for modern astrophysics, since space plasmas are the only extraterrestrial plasmas available for detailed in situ study and comparison of theory with data. Plasma physics is the basic underlying sub-discipline of physics. The reason is that these regions all contain plasmas, the so-called "Fourth State of Matter", in which atoms are either partially or fully ionized into electrons and ions, thereby being strong influenced by electromagnetic waves and vice-versa.