Rationale For Landing Sites At Lunar Pyroclastic Deposits

Lisa Gaddis
Abstract Title: 
Rationale For Landing Sites At Lunar Pyroclastic Deposits
Abstract Type: 
Abstract Body: 
RATIONALE FOR LANDING SITES AT LUNAR PYROCLASTIC DEPOSITS. Lisa Gaddis1, Laszlo Kestay1, Marc Hunter1, Julie Stopar2, Samuel Lawrence3, Briony Horgan4, Marie McBride4. 1Astrogeology Science Center, U. S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001; 2Lunar and Planetary Institute, Houston, TX; 3NASA Johnson Space Center, Houston, TX; 4Purdue University, W. Lafayette, Indiana. (lgaddis@usgs.gov). Introduction: Lunar pyroclastic deposits are widely distributed across the Moon, typically occurring adjacent to basaltic mare deposits [1]. Both small to very large (~10 km2 and 50,000 km2) lunar pyroclastic deposits have been recognized as dark, rock-free, glass-rich units that mantle underlying terrain. A major component of the sampled pyroclastic deposits at Apollo 17 (Taurus Littrow) and 15 (Hadley Rille) landing sites are picritic glass and crystallized beads [2, 3]. These primitive materials were likely derived from depths up to 400 km and they provide clues to the nature of the early lunar interior, especially regarding endogenic volatiles [3-5] and the distribution of potential resource materials [6, 7]. The concentration and source of such volatiles may have major implications for the interior structure, composition, and origin of the Moon [e.g., 9, 10]. Resource Potential: In addition to being a source of iron, titanium, and oxygen because of their relatively high mafic mineral content [11], pyroclastic glasses and beads often have surficial vapor-deposited coatings of volatile-element compounds that may be valuable resources. More than 25 volatile elements have been identified [e.g., Au, Ag, Cu, Cd, F, S, Zn; 12]. Evidence of indigenous magmatic water also was found in melt inclusions in lunar pyroclastic glass samples [e.g., 13-15]. Using hyperspectral Moon Mineralogy Mapper data, Milliken and Li [16] have mapped the abundance and distribution of lunar indigenous water and these show a notable relationship to the sites of lunar explosively emplaced volcanic deposits, with local enrichments of up to 300-400 ppm H2O. The enrichment in iron and titanium oxide (typically in the mineral ilmenite) of glass and devitrified beads [6] also allows them to retain solar wind-implanted volatiles, including H and He isotopes [e.g., 17]. Helium-3 (3He) in mature lunar regolith has been proposed as a possible fuel for nuclear fusion reactions [18]. Accessibility and Traversability: All of the larger lunar pyroclastic deposits, notably those at Aristarchus (26.7⁰N, 52.3⁰W), Sulpicius Gallus (21.7⁰N, 9.4⁰E), Sinus Aestuum (6.6⁰N, 5.9⁰W) and Rima Bode (11.9⁰N, 3.4⁰W) are on the lunar near side [1]. Should a south polar landing site be selected, the small pyroclastic at Schrödinger crater (75⁰S, 132.4⁰W), is reasonably accessible for traverse science [19]. Numerous authors have described the suitability of the fine-grained pyroclastic mantle at these sites, and at smaller near side deposits such as those in Alphonsus crater (-13.6⁰S, -4.1⁰W), for meeting science and engineering requirements for planning lunar traverses [20-24]. At any of the larger pyroclastic dark mantling deposits, detailed mapping is supported by high-resolution image data from the NASA LROC NAC [25] and the JAXA Kaguya Terrain Camera [26] and Multiband Imager [27]. Characterization would include assessment of local and regional slopes, and the presence and position of rocks and boulders associated with impact craters and slopes. Preliminary assessments point to numerous safe landing sites near resource-bearing pyroclastic deposits, making these prime destinations for future robotic precursor missions. The 2016 LEAG update of the strategic knowledge gaps for the “Moon First” exploration scenario [28] highlighted the need for in-situ measurements of geotechnical properties (particularly size fraction and penetrability) as well as understanding the depth of the regional pyroclastic deposits as key measurements to enhance human exploration scenarios. References: [1] Gaddis et al., 2003, Icarus 161, 262-280. [2] Heiken et al., 1974, GCA 38, 1703-1718. [3] Delano, 1986, JGR 91, D201-D213. [4] Shearer and Papike, 1993, GCA 57, 4785-4812. [5] Papike et al., 1998, ch. 5 in RIM 36, 5.1-5.234. [6] Shearer et al., 2006, RMG 60, 365-518. [6] Hawke et al., 1989, PLPSC 19th, 255. [7] Duke et al., 2006, RIMG 60, 597-656. [9] Schmitt, 2010, NASA Decadal Survey white paper. [10] NRC, 2007, The Scientific Context for Exploration of the Moon, National Acade-mies Press, 119 p. [11] Allen, 2015, 46th LPSC, 1140. [12] McCubbin et al., 2015, Am. Min. 100, 1668-1707. [13] Saal et al., 2008, Nature 454, 192-196. [14] Anand et al., 2014, Phil. Trans. R. Soc. A 372, 2130254. [15] Hauri et al., 2017, Ann. Rev. Earth Planet. Sci., 45(1). [16] Milliken & Li, 2017, Nature Geosci. 10, 561-565. [17] Fegley and Swindle, 1993, Res. Near-Earth Space, Univ. Az. Press, pp. 367-426. [18] Schmitt, 2006, Return to the Moon, Praxis. [19] Kamps et al., 2017, LPSC abs. 1909. [20] Gaddis et al., 2011, LPSC 42, abs 2691. [21] Bleacher et al. (2008), NLSI Lun. Sci. Conf., abs. 2166. [22] Stopar et al. (2013) 2013 LEAG, abs. 7038. [23] Speyerer et al. (2013) LPSC 44, abs. 1745. [24] Lawrence et al. (2014) LPSC 45, abs. 2785. [25] Robinson et al., 2010, Space Sci. Rev. 150, 81-124. [26] Haruyama et al., 2008, Adv. Sp. Res. 42, 310-316. [27] Ohtake et al., 2010, Space Sci. Rev. 154, 57-77. [28] Shearer et al., 2016, Lunar Human Exploration Strategic Knowledge Gap Special Action Team Review, see https://www.nasa.gov/sites/default/files/atoms/files/leag-gap-review-sat-2016-v2.pdf. Figure 1. 3-D view of Sinus Aestuum looking NE (~25X vertical exaggeration). False-color MI-VIS mosaic (R=750/415, G=750/950, B=415/750) showing dark blue (high Fe, Ti) pyroclastic mate-rials of SA covering the hummocky highlands (left and right, center). Copernicus crater is to the upper left (northwest) out of view, and the mantled Rima Bode region is to the northeast (upper right). Gambart crater at lower left is 25 km across.