Exploring The Moon For Recent Lunar Activity.

Charles Shearer
Abstract Title: 
Exploring The Moon For Recent Lunar Activity.
Abstract Type: 
Abstract Body: 
Introduction: During periods of volcanic activi-ty on the Moon volatiles were transported from the lunar interior to the surface and into the exosphere. These episodes of indigenous volatile release are clearly manifested in vesicles in mare basalts, as surface coating on volcanic glass beads associated with pyroclastic deposits and in volatiles in mag-matic phases (e.g., apatite, sulfides). With the de-crease to termination of mare volcanism, mecha-nisms for the delivery of volatiles to the lunar sur-face perhaps changed and decreased in frequency. Alpha Particle Spectrometers (APS) carried by the Apollo 15 and 16 missions showed spatial and tem-poral variations in radon emissions [1]. These de-gassing events have been identified to occur at Aristarchus, Grimaldi, Tsiolkovsky, and at mare edges. They may be correlated with sites of reported transient visual events [1]. Decades later the Lunar Prospector APS documented radon gas (some with very short half-lives) emanating from the vicinity of the craters Aristarchus and Kepler and other locations associated with pyroclastic deposits [2]. If analogous to terrestrial processes, the radon release was probably a fingerprint for the release of larger quantities of more common gases from the deep lunar interior to the Moon’s surface. Schultz et al. [3] proposed several structures that may be the source of cold gas release: the Ina structure, small-scale, low relief patches within the Hyginus central caldera, within dark mantling deposits on the edge of Mare Serenitatis, and within Tranquilitatis. Figures 1 and 2 illustrate characteristics of the Ina structure and are from [3,5]. Braden et al. [6] identified a feature similar to Ina referred to as the Sosigenes irregular mare patch. There has been considerable debate concern-ing the origin and age of these structures [e.g., 3-6]. There are fundamental questions that could be answered with combined orbital and in situ assets to explore potential recent degassing events on the Moon: (1) What is the origin of the “Irregular Mare Patches” identified by [3-6]? (2) Are these structures the source for recent radon emissions events measured during the Apollo Program and the Lunar Prospector mission? (3) What other gases are associated with the radon emissions? (4) What are the interior sources and lunar processes responsible for these degassing events? (5) How do these events affect the lunar exosphere and volatile transport on the lunar surface? Exploration Targets: Numerous potential tar-gets have been identified [1-6] that would be appro-priate for using current assets (LRO) in orbit and deploying additional assets in orbit and on the lunar surface. As the Ina structure has been studied and discussed more to date than many of these other possible vents for interior degassing, perhaps that is the target to consider first. First discovered in Apollo 15 images, the D-shaped Ina structure (Figure 1) is a shallow depres-sion located in Lacus Felicitis approximately 170 km SE of the Imbrium basin rim. It is approximate-ly 2 x 3 km and consists of rough crater-less patches between relict mounds (Figure 2). Ina has a thermal inertia lower than the surrounding terrain and this suggests that the material is less consolidated than typical regolith [7]. Potential target sites could be adjacent to the structure or on an interior mound. In situ instruments could be used to detect degassing events and examine the local regolith. Additional Earth- and orbital-based observations may be used to further document this target.
C. Shearer1, P. Schultz2, and N. Petro3. 1 Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87122; 2 Department of Geological Sciences, Brown University, Providence, Rhode Island 02912; 3Goddard Space Flight Center, Greenbelt, MD 20771.