Martian Ionosphere: A Component Due to Solar Protons
Carl Sagan 1 and
Joseph Veverka 1
1 Harvard University and Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 02138
The small magnetic field strength observed near Mars by Mariner IV suggests that protons from the solar wind may enter the Martian atmosphere and produce ionization in addition to that produced by ultraviolet light and x-rays. It is found that solar protons produce a thin ionized layer at a rate of the order of 3 x 103 per cubic centimeter per second at a depth corresponding to the F1 region in the terrestrial atmosphere. Unless the effective recombinative coefficient is very large (greater than 10-5 centimeter cubed per second) or unless unusual diffusion effects are present, this layer should have been detected by Mariner IV, and therefore must be present in one of the observed ionized regions. Because of its very compact shape, the subsidiary maximum near 95 kilometers discovered in the Mariner-IV occultation experiment may be the proton ionization peak. If so, the major 120-kilometer maximum is an F2 layer. Distinction between photon and proton ionization regions can be made by microwave occultation experiments aboard planetary orbiters.
