Observations of the 10-μm natural laser emission from the mesospheres of Mars and Venus |
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| Authors: | D Deming F Espenak D Jennings T Kostiuk M Mumma D Zipoy |
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| Institution: | 1. Infrared and Radio Astronomy Branch, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA;2. Astronomy Program, University of Maryland, College Park, Maryland 20742, USA |
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| Abstract: | Nonthermal emission occurs in the cores of the 9.4- and 10.4-μm CO2 bands on Mars, and has been recently identified as a natural atmospheric laser. This paper presents observations of the total flux and center-to-limb dependence of this emission for Mars and Venus. The emission is believed to be excited by absorption of solar flux in the near-ir CO2 bands, followed by collisional transfer to the 00°1 state of CO2. A comparison is made between the observations and a detailed theoretical model based on this mechanism. It is found that the theoretical model successfully reproduces the observed center-to-limb dependence of this emission, to within the limits imposed by the spatial resolution of the observations. A comparison is also made between the observed fluxes and the predictions of the theoretical models. The observed flux from Mars agrees closely with the prediction of the model; the flux observed from Venus is 74% of the flux predicted by the model. This emission is utilized to obtain the kinetic temperatures of the Martian and Venusian mesospheres. For Mars near 70 km altitude, a rotational temperature analysis using five lines gives T = 135 ± 20°K. The frequency width of the emission is also analyzed to derive a temperature of 126 ± 6°K. In the case of the Venusian mesosphere near 109 km, the frequency width of the emission gives T = 204 ± 10°K. |
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