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[3.04] Meridional Mapping of Mesospheric Temperatures from CO₂ Emission along the MGS Ground Track

T.A. Livengood (Challenger Ctr.), T. Kostiuk, K.E. Fast, J.N. Annen (NASA's GSFC), G. Sonnabend (NAS/NRC at GSFC), T. Hewagama (U. of MD)

On June 6--15, 2003, we observed the narrow 10.6~\mum infrared emission feature (~0.0016~cm^-1) of normal-isotope carbon dioxide originating in the mesosphere of Mars, superposed on the relatively broad (~ 0.02~cm^-1) absorption feature of tropospheric CO₂. Spectra of the emission core were acquired at a spectral resolving power of \lambda / \Delta\lambda = 5\times 10⁶ using the Heterodyne Instrument for Planetary Winds and Composition (HIPWAC) at the NASA Infrared Telescope Facility. Lower-resolution spectra (\lambda / \Delta\lambda = 1\times 10⁶) acquired simultaneously characterize the wings of the ``broad'' absorption feature. Thermal profile information to an altitude of ~40~km is recorded in the shape of the tropospheric line; mesospheric temperatures at ~60--80~km are recorded by the Doppler width of the emission feature. These data thus provide a measure of Mars' thermal profile over a broad range of altitude, complementing results from the Mars Global Surveyor (MGS) TES instrument for the troposphere and providing the only remote method to experimentally determine temperatures in the mesosphere. Spectra of a single CO₂ line were obtained from 9 positions spaced 15^\circ in latitude along the 2PM meridian ground track of the MGS spacecraft between 45^\circN latitude and 75^\circS latitude, providing temperatures at each location. Spectra were acquired at the equator at six other CO₂ lasing transitions in order to constrain the rotational temperature for comparison to the kinetic temperature derived from the Doppler width of the emission core. In addition to the expected strong normal-isotope lasing transitions appearing in Mars' atmosphere, two additional classes of features were detected at high signal-to-noise ratio: relatively weak secondary lines of CO₂ were observed near several lasing transitions, and features of ¹⁶O¹²C¹⁸O (628 carbon dioxide) were detected with high statistical significance.

This work is supported by the NASA Planetary Astronomy Program.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.