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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.05.011 Byline: Bradley J. Thomson (a), Peter H. Schultz (b) Keywords: Mars; Mars; surface; Geological processes; Cratering Abstract: Reevaluating the geologic history of the prior Mars landing sites provides important ground truth for recent and ongoing orbital missions. At the Viking 2 Lander (VL2) site, topographic measurements of relict landforms indicate that at least 100 m of sedimentary mantle material has been stripped away. The observed paucity of impact craters Author Affiliation: (a) NASA-Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-501, 4800 Oak Grove Dr., Pasadena, CA 91109, USA (b) Department of Geosciences, Brown University, Box 1846, Providence, RI 02912, USA Article History: Received 19 December 2006; Revised 10 May 2007

The scarcity of impact craters on Venus make it difficult to infer the relative ages of geologic units. Stratigraphic methods can be used to help infer the relative ordering of surface features, but the relatively coarse resolution of available radar data means ambiguity about the timing of certain features is common. Here we develop a set of statistical tools in MATLAB to help infer the relative timing between clusters of small shield volcanoes and sets of fractures in the surrounding terrain. Specifically, we employed two variants of the two-point azimuth method to detect anisotropy in the distribution of point-like features. The results of these methods are shown to successfully identify anisotropy at two spatial scales: at the whole-field level and at scales smaller than a set fraction of the mean value. Initial results on the test cases presented here are promising, at least for volcanic fields emplaced under uniform conditions. These methods could also be used for detecting anisotropy in other point-like geologic features, such as hydrothermal vents, springs, and earthquake epicenters. [ABSTRACT FROM AUTHOR]

Laboratory spectral libraries of well-characterized natural samples are necessary for accurate interpretation of remote sensing spectral data. Tephra deposits, the result of explosive volcanic eruptions, are potentially found on all differentiated terrestrial bodies and are important chronologic and compositional marker beds on Earth. Here we present a visible/near-infrared (VNIR, 0.35–2.5 μm) and mid-infrared (MIR, 3.5–25 μm) spectral library composed of nineteen natural tephra samples from ten volcanic sources that span a range of compositions and components. The bulk, glass, and mineral phase compositions of each sample are measured and spectra from multiple size fractions of each sample were collected. The library can be found via the Terrestrial Analog portal (DOI: https://doi.org/10.5066/P9O54M4Q). • Library of visible-near-infrared and mid-infrared spectra of tephra samples. • Tephra span wide-range of terrestrial compositions, including alkaline endmembers. • Tephra compositions and phase assemblages were characterized. [ABSTRACT FROM AUTHOR]