Theplasmasphere, orinnermagnetosphere, is a region of theEarth's magnetosphere consisting of low-energy (cool)plasma. It is located above theionosphere. The outer boundary of the plasmasphere is known as theplasmapause, which is defined by an order of magnitude drop in plasma density. In 1963 American scientistDon Carpenter and Soviet astronomerKonstantin Gringauz [ru] proved the plasmasphere and plasmapause's existence from the analysis ofvery low frequency (VLF)whistler wave data. Traditionally, the plasmasphere has been regarded as a well behaved cold plasma with particle motion dominated entirely by thegeomagnetic field and, hence, co-rotating with the Earth.
The discovery of the plasmasphere grew out of the scientific study ofwhistlers, natural phenomena caused by very low frequency (VLF) radio waves. Whistlers were first heard by radio operators in the 1890s.[1] British scientistLlewelyn Robert Owen Storey had shownlightning generated whistlers in his 1953 PhDdissertation.[1][2] Around the same time, Storey had posited the existence of whistlers meant plasma was present inEarth's atmosphere, and that it moved radio waves in the same direction asEarth's magnetic field lines.[1][2] From this he deduced but was unable to conclusively prove the existence of the plasmasphere.[2] In 1963 American scientistDon Carpenter and SovietastronomerKonstantin Gringauz—independently of each other, and the latter using data from theLuna 2 spacecraft—experimentally proved the plasmasphere and plasmapause's existence, building on Storey's thinking.[1]
In 1965 Storey and French scientist M. P. Aubry worked onFR-1, a Frenchscientific satellite equipped with instruments for measuring VLF frequencies and the localelectron density of plasma. Aubry and Storey's studies of FR-1 VLF and electron density data further corroborated their theoretical models: VLF waves in the ionosphere occasionally passed through a thin layer of plasma into the magnetosphere,normal to the direction of Earth's magnetic field.[3]: 1181 [4] Throughout the 1970s, Storey continued studying VLF waves using data gathered by FR-1.[2] Data received from the VLF receiver onOV3-3, launched 4 August 1966, determined the location of the plasmapause.[5]
In 2014satellite observations from theTHEMIS mission have shown that density irregularities such as plumes or biteouts may form.[6][7] It has also been shown that the plasmasphere does not always co-rotate with the Earth. The plasma of the magnetosphere has many different levels of temperature and concentration. The coldest magnetospheric plasma is most often found in the plasmasphere. However, plasma from the plasmasphere can be detected throughout the magnetosphere because it gets blown around by the Earth's electric and magnetic fields. Data gathered by the twinVan Allen Probes show that the plasmasphere also limits highly-energeticultrarelativistic electrons fromcosmic andsolar origin from reaching low earth orbits and the surface of the planet.[8][9]
