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Lunar Basins – the Moon's Big Bangs

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Lunar Basins – the Moon's Big Bangs OH/H20 Enhancements associated with Some Silicic Volcanism as detected by M3 Noah Petro LEAG Annual Meeting 2014 October 23, 2014 H/T Carlé Pieters, Rachel Klima, Brad Jolliff, Lillian Ostrach, Tim Glotch, Josh Bandfield It all starts with Roger Clark Clark et al. (2011) Wet vs. Dry Moon workshop Bullialdus Crater (Klima et al., 2013) Clark et al. (2011) Wet vs. Dry Moon workshop 3 OH/H2O with M • “Polar” water detection (Pieters et al., 2009; Clark et al., 2012) • Bullialdis Central Peak (80 ppm +/- 40 ppm) [Klima et al., 2013] Compton-Belkovich Lunar Prospector Thorium • Thorium enhancement measured by LP • Silicic volcanic complex, ~20 x 30 km • Morphological evidence for small domes and collapse features • Offset of Th due to a pyroclastic eruption? (Jolliff et al., 2011; Wilson et al. ,2014?) Alpha Dome M3 Perspective: Data taken while Chandrayaan-1 at 200 km M3G20090601T064032 750 ~3µm Band Strength Ratio nm A ratio of two bands (2616µm and 2816 µm, B74/B79) highlights ~3 µm feature. 3µm Absorption at CB – Where it is M3G20090601T064032 ~3µm Band Strength Ratio 500m LROC NAC ROI Mosaic -CompBelkLoB 3µm Absorption at CB – Where it isn’t M3G20090601T064032 ~3µm Band Strength Ratio Alpha Dome Blocky Dome LROC NAC ROI Mosaic -CompBelkLoB 500m What is at and around 3µm? • Pieters et al. 2009 - Model near-infrared reflectance spectra of H2O and OH applicable for lunar comparisons. A model of a thin layer of H2O water (red) and ice (blue) on a 10% reflective surface equivalent to ~1000-ppm abundance is distinct from anorthite (green) and a lunar glass analog (black). The shaded area extends beyond the spectral range of M3. Detection of OH/H2O at C-B • Stronger 3µm absorption associated with C-B relative to surroundings • Strongest absorptions are associated with ~3µm Band Depth Ratio craters, some LROC NAC ROI Mosaic -CompBelkLoB seemingly fresh craters, but not all fresh craters • Blocky areas have weakest absorptions in region 500m What is the origin of the 3µm feature at Compton-Belkovich? • Data artifact, the result of thermal correction in the M3 L2 data • Not an artifact: Is there a property of the regolith at C-B relative to its surroundings? Is it due to composition and preferential trapping of OH/H2O? Endogenic? OH/H2O in Direct Association with C-B • Compton-Belkovich is enhanced in OH/H2O relative to its surroundings – C-B is indistinct from its surroundings in temperature, 750 nm ~3µm Band Ratio rock abundance, and upper regolith thickness (Diviner) – C-B does have a distinct radar signature, is rock-free, consistent with large pyroclastic deposits • OH concentration is conservatively ~100-150 ppm above than the surroundings • LAMP also sees something in the FUV associated with C-B (Hendrix et al., 2013) Dufay Albdeo Anomaly • Bright diffuse region north of main Thorium enhancement (Dewar) • Appears to be thin deposit with some small craters excavating through Mandel'shtam F 30 km DufayDiviner Albdeo CF Map Anomaly • Bright diffuse region north of main Thorium enhancement • Appears to be thin deposit with some small craters excavating through ~3µm Band Ratio Dufay Albdeo Anomaly • Bright diffuse region north of main Thorium enhancement • Appears to be thin deposit with some small craters excavating through ~3µm Band Ratio m3g20081227t090105 Hansteen Alpha • Identified in Earth-based spectra as a “red spot” • Glotch et al. (2010) showed that it is silicic • Lawrence et al. M3G20090418T190900 (2005) modeled a Lat: -12.3 Th abundance of Lon: -50.2 ~25 ppm M3 View of Hansteen Alpha A ratio of two bands (2616µm and 2816 µm, B74/B79) M3G20090418T190900_V01_RFL What is at and around 3µm? • Pieters et al. 2009 - Model near-infrared reflectance spectra of H2O and OH applicable for lunar comparisons. A model of a thin layer of H2O water (red) and ice (blue) on a 10% reflective surface equivalent to ~1000-ppm abundance is distinct from anorthite (green) and a lunar glass analog (black). The shaded area extends beyond the spectral range of M3. Is This Feature a Result of the Level 2 Processing? Is This Feature a Result of the Level 2 Processing? • No • Feature is there in Level 1B data, pre thermal removal (I/F or Apparent Reflectance) • Appears in multiple Optical Periods What’s going on? • I’m misinterpreting something (as is Klima et al.) • We’re seeing OH/H2O in direct association with silicic volcanic (possibly pyroclastics) at two similar features (C-B and Hansteeen Alpha) and the deposit (pyroclastic?) near Dufay – Not all silicic volcanoes (Lassell Massif, Marian Domes) or Th hotspots (SPA) have such features – Perhaps a slight enhancement at the Gruithuisen Domes Dufay C-B Hansteen Alpha .
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