36th DPS Meeting, 8-12 November 2004
Session 45 Mars Surface and Water II
Oral, Friday, November 12, 2004, 1:30-3:00pm, Lewis

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[45.08] Global-Scale Maps of Near-Infrared Spectral Variability on Mars: Analysis of 2003 Mars Opposition Observations from HST/NICMOS

E.Z. Noe Dobrea, J.F. Bell III (Cornell University, Department of Astronomy), M.J. Wolff (Space Science Institute), K. Noll, A. Lubenow (Space Telescope Science Institute)

We have used HST/NICMOS to observe Mars in 7 narrow band filters (0.97, 1.08, 1.13, 1.66, 1.90, 2.12, and 2.15 \mu m) during the 2003 opposition. Observations were acquired on August 21, 22, 28, and 29, 2003. The data were calibrated using the standard pipeline calnica and calnicb procedures [1], then were converted to I/F, corrected for limb darkening, co-registered, and projected to Mollweide equal-area projection. Approximately 57% of the surface was imaged during the 2003 campaign, at a spatial resolution of ~ 20 km/pixel near the sub-Earth point.

We have used principal components analysis (PCA) to identify regional variability on scales of 100s of km associated with variations in the near-infrared spectrum of Mars. Visualization of the data cloud in principal component space has allowed us to identify spectral endmembers associated with 1) the South Polar Cap, 2) Acidalia Planitia, 3) Syrtis Major, and 4) the Classical Bright Terrains of Tharsis.

Particularly interesting is the strong variability in the 0.97-2.15 \mu m spectral slope (up to 36% variation in slope), whose magnitude is most negative for the classical dark terrains and least negative for the bright terrains. However, strong variations in this spectral slope are exhibited among the dark terrains and some classical intermediate terrains. The most negative value is measured in Acidalia Planitia (30\arcdegW, 45\arcdegN), whereas the least negative value, measured in Tyrrhena Terra (285\arcdegW, 15\arcdegS), is as low as that of the bright terrains. This variability is most apparent between Syrtis Major (290\arcdegW, 13\arcdegN) and Tyrrhena Terra. Although some features in the 0.97:2.15-\mu m ratio map can be associated with classical albedo patterns, the map generally shows no correlation to albedo, topography, or geology, suggesting that surface physical or compositional/mineralogic effects are responsible for the observed variations. Constrains on the mineralogy responsible for the observed effect will be discussed.

[1] http://www.stsci.edu/hst/nicmos/documents/handbooks/current_NEW/nicmos_instr_handbookTOC.html

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.