Upper Atmospheres of the Planets.

Abstract

view Abstract Citations (40) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Upper Atmospheres of the Planets. Chamberlain, Joseph W. Abstract Most of our knowledge of the earth's upper atmosphere is obtained from experiments in sit or remote observations that offer fairly direct interpretations. For the other planets, neither approach is as yet possible; so indirect, theoretical procedures are required to construct models of their atmospheres. Herein the wide variety of basic physical processes governing the structure of a planetary high atmosphere are set forth, with a view toward obtaining "deductive models' `-i e, models derived theoretically when only the chemical composition and temperature of the lower atmosphere and the incident solar flux are specified (in addition to various physical and astronomical constants). The procedures are applied to Mars, whose lower and middle atmosphere is already partially understood from earlier work, notably that of R. Goody. The uncertainties involved at various stages in the construction of such a model are emphasized, as are the major differences in physical processes and atmospheric characteristics between Mars and the earth. The most significant result is that the CO that must be in the upper atmosphere of Mars should serve as an effective thermostat, keeping the temperature at the escape level (1500 km) from exceeding about 11000 K. This is cool enough for Mars to retain atomic oxygen. Were it not for CO cooling, the upper atmosphere of Mars would be so extensive and form such an effective thermal insulation between the upper ionosphere and the heat sink at the mesopause that the temperature would exceed 20000 K. lifetime for the escape of oxygen is estimated as 10 years. The mesopause is determined by CO2 radiation. Near the mesopause CO2 should become dissociated and the free 0 atoms form a thin layer of O this effect has no analogy on earth. The model ionosphere has considerably smaller densities of ionization than comparable regions in the earth's atmosphere The E region is split into two distinct portions, with X-rays forming the higher one (E2) and ultraviolet light ionizing Oi near the mesopause (E1) The Martian analogue to the terrestrial F2 region may not develop a very high electron density, and the entire ionosphere should be depleted at night. Publication: The Astrophysical Journal Pub Date: September 1962 DOI: 10.1086/147409 Bibcode: 1962ApJ...136..582C full text sources ADS |