The Seasonal Behavior of Water Ice Clouds in the Tharsis and Valles Marineris Regions of Mars: Mars Obiter Camera Observations J. Benson, B. Bonev, P. James, K. Shan, B. Cantor, M. Caplinger ICARUS Presented by Kate Hale 12/9/04

Outline Objectives of the study Why is the study important? Description of technique Data Results

Objectives Quantify seasonal variations of cloud characteristics associated with certain topographical features (canyons and volcanoes) Determine periodicities in data Estimate cloud top height Determine optical depth of observed clouds to estimate their water content

Why is this study important? Past Studies: Ground based Mariners 6, 7 & 9 Viking Hubble Space Telescope ALL LIMITED None able to perform continuous, daily monitoring

Techniques of the study Data taken from March , to July 31, 2001 Mars Orbital Camera took images in both red and blue bandpass range –In blue the ice clouds appear very bright (high scattering albedo) separating them from the darker dust clouds In 24-hr period a complete global map is obtained of resolution = 7.5 km/pixel (Daily Global Maps) –However some missing data at times due to solar conjunction and incomplete data reception at Deep Space Network (~19 Martian days) Visually located areas of high cloud density, then matched with blue images and cloud area measured Thermal Emission Spectrometer (TES) data complemented visual images

Data - 4 Tharsis region volcanoes A)Arsia Mons (1 ˚ S, 130 ˚ W by 10 ˚ S, 110 ˚ W)* May 2001 B)Alba Patera (50˚N, 128˚W by 30˚N, 99˚W)* Dec 2000 C)Ascraeus Mons (25˚N, 129˚W by 2˚N, 88.5˚W)* February 2001 D)Pavonis Mons (11˚N, 127˚W by 8˚S, 105˚W)* February 2001 Ripple “W” cloud (large, bright, limb clouds) From (C) Formed from upward slope of volcano From (D) *Window coordinates: (left top, right bottom)

Data- Seasonal for Volcanoes Aerocentric Longitude: Angle of Mars in its orbit around the sun, measured from the vernal equinox (Ls = 0 starting northern hemisphere’s Spring season) Observations: - Olympus and Ascraeus are similar - Arsia has constant cover - Pavonis Mons had double peak

Alba Patera Alba Patera also has double peak (highest peak at 1.2 million km 2 ) Anticorrelated with Olympus and Ascraeus

Data Cloud height taken for several days throughout cloudy season. - Visual inspection of position relative to volcano compared against topographical maps of the volcanoes Cloud optical depth was calculated from blue images and the radiance (albedo) of the clouds using the 3 layer model which was used in modeling Hubble’s observations. - Observed radiance compared with outside point surface albedo - TES data used to estimate dust optical depth Water column abundances were calculated from final calculated cloud depths

Results Overlapping of data shows that there is seasonal repeatability for the Tharsis volcanoes, Olympus Mons, and Alba Patera Cloud area on short scale (< sols) intensifies in both size and thickness as the day progresses Clouds at Valles Marineris are in form of haze from Spring to mid-Summer, then small discrete clouds until end of Summer. Cloud heights increase as day progresses –Range for Alba Patera 5.5 – 6.5 km compared to –Olympus Mons 19 – 21 km H 2 O abundances range from pr μm for Arsia Mons to.101 – pr μm (pr μm = precipitable microns)

References Paper presented: Benson, J., B. Bonev, P. James, K. Shan., B. Cantor, M. Caplinger. “The Seasonal Behavior of Water Ice Clouds in the Tharsis and Valles Marineris Regions of Mars: Mars Obiter Camera Observations.” ICARUS 165 (p34-52), Beish, Jeff. “Discrete Topographic Orographic Clouds of Mars.” Association of Lunar and Planetary Observers. Davies, Donald. “The Mars Water Cycle.” Academic Press, ICARUS 45, 1981.