TY - JOUR
T1 - Global-scale near infrared variability on Mars
T2 - Analysis of 2003 Mars opposition observations from HST/NICMOS
AU - Noe Dobrea, E.
AU - Bell, J. F.
AU - Wolff, M. J.
AU - Noll, K.
AU - Lubenow, A.
AU - Million, C. C.
N1 - Funding Information:
We thank the operations and support staff at the Space Telescope Science Institute (STScI) for their assistance with the collection and calibration of these HST observations. We also thank Wendy Calvin and an anonymous reviewer for providing excellent comments that improved the quality of the paper. Support for HST General Observer Program GO 9738 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS5-26555. Subsequent support for our data reduction and analysis work was provided by NASA Planetary Geology and Geophysics program grant NNG04G163G. We thank the two anonymous reviewers for the helpful suggestions on an earlier draft of this paper.
PY - 2008/1
Y1 - 2008/1
N2 - We have used HST/NICMOS to observe approximately 57% of the martian surface in 7 narrow band filters (0.97, 1.08, 1.13, 1.66, 1.90, 2.12, and 2.15 μm) during the 2003 opposition (Ls ∼ 250 °) and at a resolution of ∼12 km/pixel. Principal components analysis (PCA) of the dataset has identified regional variability on scales of hundreds of kilometers associated with differences in the near-infrared spectrum of Mars. Visualization of the data in principal component space has allowed us to identify spectral endmembers associated with the south polar cap, the classic bright terrains, northern Syrtis Major, southern Syrtis Major, Tyrrhena Terra, and Acidalia Planitia. The two Syrtis Major endmembers and the Tyrrhena Terra endmember differ in their absolute reflectivities but have the same spectral shape at wavelengths longer than 1.6 μm. The Acidalia endmember is distinct from the other dark terrain endmembers because it exhibits a strong negative near-IR spectral slope. Comparisons with spectral library measurements cannot provide unique constraints on the surface mineralogy for these sparsely-sampled spectral data. However, the observed spectral variations between Tyrrhena Terra and Syrtis Major are consistent with variations in iron- and sulfur-bearing minerals, and the relatively strong negative spectral slope in the spectrum of Acidalia is consistent with the presence of hydrated alteration products. Additional comparison with previous NICMOS observations taken in 1997 at Ls ∼ 150 ° indicate that the average near-IR spectral slope of the Acidalia region is more negative during the late northern fall than during the mid northern summer. This may indicate seasonal variations in the presence of either adsorbed water or re-hydrated minerals in the regolith of Acidalia.
AB - We have used HST/NICMOS to observe approximately 57% of the martian surface in 7 narrow band filters (0.97, 1.08, 1.13, 1.66, 1.90, 2.12, and 2.15 μm) during the 2003 opposition (Ls ∼ 250 °) and at a resolution of ∼12 km/pixel. Principal components analysis (PCA) of the dataset has identified regional variability on scales of hundreds of kilometers associated with differences in the near-infrared spectrum of Mars. Visualization of the data in principal component space has allowed us to identify spectral endmembers associated with the south polar cap, the classic bright terrains, northern Syrtis Major, southern Syrtis Major, Tyrrhena Terra, and Acidalia Planitia. The two Syrtis Major endmembers and the Tyrrhena Terra endmember differ in their absolute reflectivities but have the same spectral shape at wavelengths longer than 1.6 μm. The Acidalia endmember is distinct from the other dark terrain endmembers because it exhibits a strong negative near-IR spectral slope. Comparisons with spectral library measurements cannot provide unique constraints on the surface mineralogy for these sparsely-sampled spectral data. However, the observed spectral variations between Tyrrhena Terra and Syrtis Major are consistent with variations in iron- and sulfur-bearing minerals, and the relatively strong negative spectral slope in the spectrum of Acidalia is consistent with the presence of hydrated alteration products. Additional comparison with previous NICMOS observations taken in 1997 at Ls ∼ 150 ° indicate that the average near-IR spectral slope of the Acidalia region is more negative during the late northern fall than during the mid northern summer. This may indicate seasonal variations in the presence of either adsorbed water or re-hydrated minerals in the regolith of Acidalia.
KW - Mars
KW - Spectroscopy
KW - surface
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U2 - 10.1016/j.icarus.2007.07.026
DO - 10.1016/j.icarus.2007.07.026
M3 - Article
AN - SCOPUS:36749044237
VL - 193
SP - 112
EP - 124
JO - Icarus
JF - Icarus
SN - 0019-1035
IS - 1
ER -