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Nonthermal escape of the atmospheres of Venus, Earth, and Mars

TitleNonthermal escape of the atmospheres of Venus, Earth, and Mars
Publication TypeJournal Article
Year of Publication1996
AuthorsShizgal, BD, Arkos, GG
JournalReviews of Geophysics
Volume34
Pagination483-505
Date PublishedNov
Type of ArticleReview
ISBN Number8755-1209
KeywordsCHARGE-EXCHANGE, dissociative recombination, FRACTIONATION, HOT OXYGEN GEOCORONA, MAGNETIC-FIELD, MAGNETOHYDRODYNAMIC MODEL, MARTIAN ATMOSPHERE, mass, MULTISPECIES, NITROGEN-ATOMS, SOLAR-WIND INTERACTION, ULTRAVIOLET SPECTROMETER EXPERIMENT
Abstract

Atmospheric loss from planetary atmospheres is an important geophysical problem with implications for planetary evolution. This is a multidisciplinary research field that requires an expertise in a wide range of subjects including statistical mechanics, fluid mechanics, plasma physics, collision theory, and surface science. This paper is a review of the current state of our understanding of atmospheric loss from the terrestrial planets. A detailed discussion is provided of the basic concepts required to understand the processes occurring in the high-altitude portion of a planetary atmosphere referred to as the exosphere. Light atomic species with sufficient translational energy can escape from an atmosphere. The translational energy required for escape could be thermal energy and proportional to the ambient temperature or the result of some collisional processes energizing the species above thermal energies. These collisional processes, which include charge exchange and dissociative recombination between energetic ions, neutrals, and electrons, are referred to as nonthermal escape processes. We highlight the similarities and differences in the important escape mechanisms on the terrestrial planets and comment on application of these mechanisms to evolutionary theories of the terrestrial atmospheres. The emphasis in this paper is directed toward the need to consider the exosphere as collisional.

URL<Go to ISI>://A1996VU91900004