The Martian O2 and H2O cycles observed with ChemCam Passive Sky Spectroscopy

Friday, 19 December 2014: 1:40 PM
Timothy H McConnochie1, Michael D Smith2, Steven C Bender3, Michael J Wolff4, Jeffrey Roy Johnson5, Mark T Lemmon6, Roger C Wiens7, Sylvestre Maurice8, Olivier Gasnault9, Diana Blaney10, Lauren P DeFlores10, Ari-Matti Harri11, Osku Kemppinen11, Maria Genzer11, John E Moores12, Michael H Wong13, Melissa G Trainer2, Javier Martín-Torres14, Maria-Paz Zorzano14, Heather Franz15, Bruce Lee Barraclough3, Sushil K Atreya16 and Paul R Mahaffy2, (1)University of Maryland College Park, Department of Astronomy, College Park, MD, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)Planetary Science Institute Los Alamos, Los Alamos, NM, United States, (4)Space Science Institute Boulder, Boulder, CO, United States, (5)Applied Physics Laboratory, Laurel, MD, United States, (6)Texas A & M University, College Station, TX, United States, (7)Los Alamos National Laboratory, Los Alamos, NM, United States, (8)IRAP, Toulouse, France, (9)Universite de Toulouse, Toulouse Cedex 4, France, (10)Jet Propulsion Laboratory, Pasadena, CA, United States, (11)Finnish Meteorological Inst, Helsinki, Finland, (12)York Universite, Earth and Space Science and Engineering, Toronto, Canada, (13)University of California Berkeley, Berkeley, CA, United States, (14)Centro de Astrobiologia, Madrid, Spain, (15)NASA Goddard Space Flight Center, Center for Research and Exploration in Space Science and Technology, Greenbelt, MD, United States, (16)University of Michigan Ann Arbor, Ann Arbor, MI, United States
The Mars Science Laboratory’s (MSL) ChemCam spectrometer, designed primarily for laser-induced breakdown spectroscopy, has proven to also be every effective as a passive spectrometer. We will describe measurements O2, H2O, and aerosols from ChemCam passive sky observations. We will then discuss the evidence they provide for a seasonally active Martian O2 cycle as well as their implications for the Martian water cycle.

ChemCam passive sky observations proceed by acquiring spectra of scattered light from the atmosphere at two different elevation angles, constructing a ratio spectrum to eliminate the solar spectrum and instrument response uncertainties, and then fitting a discrete ordinates multiple scattering radiative transfer model.

O2 was thought to have a long, greater than 10 Martian year, photochemical lifetime (e. g. Krasnopolsky 2010, Icarus 207) and thus was expected to show a seasonal behavior identical to other non-condensable inert gases. ChemCam measurements demonstrate that this is not the case, showing that O2 decreases rapidly relative to SAM-QMS-measured Ar and CRISM-measured CO during the Ls = 350° to Ls = 30° period and then doubles its mixing ratio relative to those gases during the Ls = 50° to Ls = 130° period. SAM-QMS O2 measurements confirm the ChemCam results, showing essentially identical O2 mixing ratios and seasonal variations.

The ChemCam water vapor measurements, when combined with the in-situ sampling of the REMS humidity sensor and with global scale orbiter data sets, provide information on the vertical distribution of water vapor and yield insights into the local and regional scale dynamics in the vicinity of Gale Crater. We observe a close match between mixing ratios inferred from REMS humidity sensor measurements and column average mixing ratios inferred from ChemCam in some seasons, but significant differences in other seasons, suggesting seasonal variations in vertical mixing processes.