P21A-2066
Probing the Martian Atmosphere with MAVEN/IUVS Stellar Occultations

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Hannes Gröller1, Roger V Yelle1, Tommi Koskinen1, Franck Montmessin2, Gaetan Lacombe2, Nicholas McCord Schneider3, Justin Deighan4, Ian F Stewart4, Sonal Jain4, Michael Chaffin4, Matteo Michael James Crismani4, Arnaud Stiepen3, Franck Lefèvre2, Bill McClintock4, John T Clarke5, Greg Holsclaw4, Paul R Mahaffy6, Stephen W Bougher7 and Bruce Martin Jakosky4, (1)University of Arizona, Tucson, AZ, United States, (2)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (5)Boston University, Boston, MA, United States, (6)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (7)University of Michigan Ann Arbor, Ann Arbor, MI, United States
Abstract:
We present the first results of FUV and MUV stellar occultations taken with the Imaging UltraViolet Spectrometer (IUVS) onboard MAVEN. The FUV and MUV channels of the IUVS together cover the spectral range from 115 to 330 nm.

The first two campaigns were executed during March 24 and March 26, 2015, and during May 17 and May 18, 2015, respectively. So far 13 occultations could be used to retrieve CO2 and O2 number densities in the altitude range between 100 and 150 km from the first occultation campaign. From the second occultation campaign number densities for CO2, O3, and aerosols were obtained between 20 and 100 km altitude.

Temperature profiles for the same altitude ranges were calculated by applying the constraint of hydrostatic equilibrium to the CO2 densities. With a cadence of 2.6 s, including a 2.0 s integration time, the altitude resolution of the density and temperature profiles is between 1.5 and 4.5 km, depending on the geometry of the particular occultation.

The retrieved density profiles of CO2 and O2 agree with previous measurements obtained by the Mars Express SPICAM instrument and by Viking 1 and 2. The corresponding O2 mixing ratios range from 1 to 5 x 10-3, also in agreement with previous observations. The temperatures that we retrieved agree with the models in the Mars Climate Database (MCD) between 10-2 and 10-4 Pa. At lower pressures, however, the measured temperatures are on average 70 K to 100 K cooler than the temperatures predicted by the MCD. This is because the model temperatures increase steadily with altitude above the mesopause whereas the observed temperatures decrease at pressures less than 3.5 x 10-5 Pa, reaching a minimum near 7 x 10-6 Pa. The large differences between the MCD and our results indicate that global models of thermal structure around the mesopause need to be revised.

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