The plasmasphere, also called the inner magnetosphere, is a part of Earth's magnetosphere that contains plasma with less energy. It is found above the ionosphere. The outer edge of the plasmasphere is called the plasmapause, which is where the plasma density drops by a large amount. In 1963, American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz proved the plasmasphere and plasmapause exist by studying data from very low frequency (VLF) whistler waves. Usually, the plasmasphere is considered a cold plasma where particles move mainly because of Earth's magnetic field and rotate along with Earth.

History

The discovery of the plasmasphere came from the study of whistlers, natural events caused by very low frequency (VLF) radio waves. Radio operators first heard whistlers in the 1890s. In 1953, British scientist Llewelyn Robert Owen Storey showed that lightning could create whistlers in his PhD dissertation. Around the same time, Storey suggested that the presence of whistlers meant plasma existed in Earth's atmosphere and that plasma moved radio waves in the same direction as Earth's magnetic field lines. From this, he figured out but could not prove the plasmasphere existed. In 1963, American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz independently proved the plasmasphere and plasmapause existed. Gringauz used data from the Luna 2 spacecraft, while Carpenter used other methods. Both built on Storey's earlier ideas.

In 1965, Storey and French scientist M. P. Aubry studied FR-1, a French satellite designed to measure VLF frequencies and the density of plasma electrons. Their analysis of data from FR-1 supported their models, showing that VLF waves in the ionosphere sometimes passed through a thin plasma layer into the magnetosphere, moving perpendicular to Earth's magnetic field. During the 1970s, Storey continued studying VLF waves using data from FR-1. Information from the VLF receiver on OV3-3, launched on August 4, 1966, helped scientists locate the plasmapause.

In 2014, satellite data from the THEMIS mission showed that density irregularities, such as plumes or biteouts, can form in the plasmasphere. It was also found that the plasmasphere does not always move with Earth. Magnetospheric plasma has varying temperatures and concentrations. The coldest plasma is usually found in the plasmasphere. However, plasma from the plasmasphere can be found throughout the magnetosphere because Earth's electric and magnetic fields push it around. Data from the Van Allen Probes revealed that the plasmasphere also blocks highly energetic ultrarelativistic electrons from space, preventing them from reaching Earth's surface or low Earth orbits.