Mapping the Near-Subsurface Structure of Lunar Pyroclastic Deposits

Abstract:

Pyroclastic deposits on the Moon are associated with a variety of settings, including domes, fractured crater floors, and rilles. Many of the largest pyroclastics, such as Aristarchus and Sulpicius Gallus are associated with rille volcanism, and mapping changes in the near-subsurface structure of these deposits can provide insight into the formation of these large deposits. This type of mapping can also highlight possible source regions. A comparison of multiple radar wavelengths (Arecibo/Green Bank 12.6 cm and 70 cm wavelength radar, Lunar Reconnaissance Orbiter Mini-RF 12.6 cm wavelength radar) with other LRO datasets (LRO Diviner and LRO Camera) has revealed changes in deposit thickness and structure around lunar rilles, including those associated with the large lunar pyroclastic deposits. For example, areas of thicker, rock-poor pyroclastics are identified that may indicate longer duration eruptions from parts of the rille. In most cases, the thickest, most block-free parts of the deposit occur near the ends of rilles. For some rilles, pyroclastics identified with radar are not visible in Diviner thermal infrared products, suggesting that there is a regolith-like surface that prevents the thermal wave from detecting deeper fine-grained materials. This upper surface could be produced by a shallow burial of the pyroclastics by regolith, or perhaps by a shift in volcanic style. Rille pyroclastics display a wide variety of correlation behaviors between the different wavelengths of data, suggesting that they have very different near-surface vertical structures. In this presentation we will focus on near-side rilles and pyroclastics in the Mare Serenitatis, Mare Vaporum, and Sinus Aestuum regions.