HR: 15:25h
AN: P12C-08    [PDF]
TI: Preliminary GRS Measurement of Chlorine Distribution on Surface of Mars
AU: * Keller, J M
EM: jkeller@lpl.arizona.edu
AF: University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721 United States
AU: Boynton, W V
EM: wboynton@gamma1.LPL.Arizona.EDU
AF: University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721 United States
AU: Taylor, G J
EM: gjtaylor@higp.hawaii.edu
AF: University of Hawaii, Hawaii Inst. of Geophysics and Planetology, Honolulu, HI 96822 United States
AU: Hamara, D
AF: University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721 United States
AU: Janes, D M
AF: University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721 United States
AU: Kerry, K
AF: University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721 United States
AB: Ongoing measurements with the Gamma Ray Spectrometer (GRS) aboard Mars Odyssey provide preliminary detection of chlorine at the surface of Mars. Summing all data since boom deployment and using a forward calculation model, we estimate values for chlorine concentration at $5\deg$ resolution. Rebinning this data and smoothing with a 15-degree-radius boxcar filter reveal regions of noticeable chlorine enrichment at scales larger than the original $5\deg$ resolution and allow for preliminary comparison with previous Mars datasets. Analyzing chlorine concentrations within 30 degrees of the equator, we find a negative correlation with thermal inertia ($R^{2}=0.55$) and positive correlation with albedo ($R^{2}=0.52$), indicating that chlorine is associated with fine, non-rock surface materials. Although possibly a smoothing artifact, the spatial correlation is more noticeable in the region covering Tharsis and Amazonis than around Arabia and Elysium. Additionally, a noticeable region of chlorine enrichment appears west of Tharsis Montes ($\sim$0 to 20N, $\sim$110 to 150W) and chlorine concentration is estimated to vary in the equatorial region by over a factor of two. A simplified two-component model involving chlorine-poor rocks and a homogenous chlorine-rich fine material requires rock abundance to vary from zero to over 50%, a result inconsistent with previous measurements and models. In addition to variations in rock composition and distribution, substantial variations in chlorine content of various types of fine materials including dust, sand, and duricrust appear important in explaining this preliminary observation. Surprisingly, visual comparison of surface units mapped by Christensen and Moore (1992) does not show enrichment in chlorine associated with regions of indurated surfaces, where cementation has been proposed. Rather, Tharsis, a region of active deposition with proposed mantling of 0.1 to 2 meters of recent dust (Christensen 1986), shows the greatest chlorine signal. In light of suggested fine material formation mechanisms, this preliminary result is intriguing. Tentative models involving venting of chlorine from hydrothermal systems (Newsom 1999), enrichment of chlorine through volcanic aerosols (Settle 1979) or acid fog reactions (Banin et al 1997), and preferential deposition of a proposed salt component in Mars fines (Clark 1993), if more easily mobilized from the Martian duricrust, are viable. Finally, this preliminary measurement will be improved through further data collection by Mars Odyssey and comparisons with MER and future missions.
DE: 5415 Erosion and weathering
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 5480 Volcanism (8450)
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting