The Moon's Most Explosive Eruption: The Aristarchus Plateau As A Future Exploration Destination

Erica Jawin
Abstract Title: 
The Moon's Most Explosive Eruption: The Aristarchus Plateau As A Future Exploration Destination
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Abstract Body: 
The Aristarchus plateau in central Oceanus Procel-larum, one of the three lunar volcanic complexes, is viewed as the most diverse volcanic region on the Moon (Figure 1). The plateau contains evidence of both explosive and effusive volcanism, including the widest and deepest sinuous rille, Vallis Schröteri (Hur-witz et al., 2013), and the largest pyroclastic deposit on the Moon. In addition to its extensive volcanic history, the Aristarchus plateau contains important links to key impact events throughout lunar history; the plateau is believed to be a block of crustal material uplifted dur-ing the formation of Imbrium basin, while the Coper-nican-aged Aristarchus crater, located on the south-eastern side of the plateau, excavated a diverse suite of materials (Mustard et al., 2011). The key unit of interest for scientific and explora-tion potential on the Aristarchus plateau is the pyro-clastic deposit. This deposit has been shown to contain concentrations of water up to several hundred ppm (Milliken and Li, 2017). Recent spectral modeling re-sults confirm that the pyroclastic deposit contains mostly glass with minimal crystalline components (Figure 2 shows spectral modeling abundance of R: OL, G: OPX, B: glass) (Jawin et al., 2017). Modeled spectral fits are consistent with compositional analyses from Lunar Prospector data which suggest that the plateau contains medium to high titanium content (e.g., Elphic et al., 2002). The Aristarchus plateau is uniquely positioned to address many scientific questions crucial to lunar geo-logic history. Several specific examples include con-straining the volatile inventory of the lunar interior through assessing quenched volcanic glass in the pyro-clastic deposit; understanding the diversity of lunar volcanic eruptions, particularly the relationship be-tween explosive and effusive eruptions through inves-tigating the sinuous rilles on the plateau; and con-straining the impact history of the Moon through in-vestigating exposures of the Aristarchus plateau and Aristarchus crater ejecta. Exploring th unique geologic history of the Aristar-chus plateau also can help to answer exploration ques-tions. Pyroclastic deposits have been proposed as po-tential ISRU targets due to the presence of metals in-cluding iron and titanium within the quenched glasses, as well as oxygen and water. These types of resources could be utilized for life support, habitat construction, radiation shielding, etc. The low slopes (<2°, Figure 3) and paucity of large blocks (from low-CPR radar data, Figure 4) on large swaths of the plateau afford a wide array of potential landing sites with access to geologically interesting lo-cations. Exploring the distal areas of the plateau (black box, Figure 3) would allow for direct analyses of relatively uncontaminated pyroclastics with access to nearby sinuous rilles. Plateau material that has not been mantled by pyroclastics are also accessible in the area via ejecta around nearby craters and steep-sloped kipukas. Alternately, a landing site in the southeastern region of the plateau near the Aristarchus ejecta de-posit (white box, Figure 3) would enable analyses of excavated pyroclastic and plateau material, as well as basaltic and crustal material originating adjacent to the plateau. This location would also allow easy access to Cobra Head, the source depression of Vallis Schrö-teri which is a potential link between explosive and effusive volcanism. Mobility would not be required in these missions; in particular, the pyroclastic deposit appears to be largely homogeneous, so missions can be adapted to investi-gate similar science questions in a variety of locations. However, traversability would enable analyses of a wider diversity of samples that would result in a better understanding of the region. Fine-scale and complex analyses such as quantify-ing volatiles within pyroclastic glasses or calculating accurate radiometric ages would require samples be returned to terrestrial laboratories; however, initial characterization by a landed suite of instruments is also critical. Such instruments could include high-resolution cameras to characterize the landing site and fine-scale geology, ground-penetrating radar to con-strain subsurface layering, x-ray and gamma-ray spec-trometers for elemental characterization, a drill that could excavate subsurface units, etc. The geologic diversity of the Aristarchus plateau makes this region a critical location for future landed scientific exploration, both robotic and human. Elphic, R.C., et al. (2002), JGR, 107(E4), 8-1–8-9. Hurwitz, D.M. et al. (2013), PSS, 79-80, 1-38. Jawin, E.R. et al. (2017), LPSC XLVII, 1256 Milliken, R.E. and S. Li (2017), Nature Geoscience, 10, 561-565. Mustard, J.F. et al. (2011), JGR, 116(E6), E00G12
James W. Head, Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912 USA