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All ionospheres are not alike: Reports from other planets
Author(s) -
Nagy Andrew F.,
Cravens Thomas E.,
Waite H. J.
Publication year - 1995
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/95rg00552
Subject(s) - ionosphere , radio occultation , pluto , planet , atmosphere (unit) , venus , physics , astrobiology , astronomy , occultation , outer planets , aeronomy , geophysics , geology , meteorology
Gauss, Lord Kelvin and Stewart Balfour suggested the existence of an electrically conducting region in the terrestrial upper atmosphere already in the last century. The first direct verification of the existence of such a region came when Marconi succeeded in sending radio signals across the Atlantic. The name ionosphere was coined by R. A. Watson‐Watt in 1926. No uniform definition of the ionosphere exists; a rather broad definition might be “ the ionosphere is that region of the atmosphere (or gaseous envelope) surrounding a solar system body where significant numbers of low energy, free electrons and ions are present .” The first direct evidence for an ionosphere at a planet other than Earth came from the radio occultation measurements of electron densities by Mariner 5, as it flew by Venus on October 19, 1967. Since then spacecraft have visited all planets, except Pluto. As a minimum, radio occultation measurements of the electron densities have been obtained at all, but Mercury. However, ground‐based optical observations indicate that Mercury has a significant exosphere; thus an ionosphere, in its broad definition, must also be present. Also for Pluto, optical measurements have established the presence of an atmosphere, implying it too has an ionosphere.