A New Paradigm for Seismic Exploration of the Moon , Mars , and Beyond

Introduction: Understanding the origin and evolution of planets remains a major challenge since direct interrogation of planetary interiors other than Earth is either limited or not (yet) available. Seismic analyses provide the most detailed picture of present-day internal elastic structure and sources of seismic energy, but collecting seismic data represents a unique logistical challenge which has been successful broadly only on Earth and in a limited capacity on the Moon. Here we propose a new approach to deployments of planetary seismic instrumentation in the form of Small Aperture Seismic Arrays (SASAs), which builds on well-developed strategies utilized in a broad range of seismic source and structural studies of Earth (e.g., [1]). We submit that the SASA approach should be strongly considered in the design of future missions which include seismic instrumentation. Deployments of SASAs will lead to profound enhancement of seismic signal quality well beyond improvements in seismic instrumentation alone. SASAs can thus produce fundamentally better seismic datasets for use in constraining sources of seismicity and the internal structure of planets. In this abstract, we focus on new strategies for lunar seismic exploration, but note the natural extensions of this approach to Mars and other planetary bodies. Lunar Seismic Data: Data from the Apollo Passive Seismic Experiment (APSE) are well studied (e.g., [2,3]) and have provided first-order information regarding the distribution and style of lunar seismic sources, the radial distribution of seismic wavespeeds, and estimates of crustal thickness variations (e.g., [4-6]). Based on these results and the obvious need for more information about the lunar interior, a compelling case has been made for deploying a new seismic network on the Moon (e.g., [7,8]). A profound challenge inherent in APSE data, however , comes in the form of high amplitude ringing of seismic energy that persists following the first arrival (i.e., coda energy). This coda, which can approach 10 minutes in length and even longer for some events, precludes confident analysis of distinct seismic phases that arrive close in time to the first arrival. These later arrivals are therefore extremely difficult to observe, yet they contain the essential information needed to further define and constrain the elastic structure of the interior. The ringing is likely due to inherent structural characteristics of the Moon, including weak attenuation in the lunar interior and substantial scattering in highly fragmented regolith, dessicated crust, and lithospheric