Ultrasonic velocities of icy powdered rock with implications for seismic resource exploration on the moon

Abstract

Although water ice has been detected by satellite observations near the lunar poles, it is unknown if this ice is simply frost on the Moon's surface or if larger ice deposits exist in the subsurface. If ice is present within the subsurface, it is unknown if this ice exists as loose ice grains or as a cement that binds regolith grains together. To create an economically viable extraction and production plan for lunar water ice resources, we must characterize near-surface ice concentration and distribution at small (<10 m) spatial and depth scales. Geophysical methods that can be deployed on the Moon's surface, such as seismic surveying, could supply some of this information for future lunar mine planning. To improve our understanding of how seismic surveying may detect and characterize subsurface lunar ice, we performed laboratory ultrasonic velocity measurements of lunar regolith simulant with variable amounts of granular and cementing ice. These measurements were performed under variable confining pressure (0.005–0.08 MPa) and constant low temperature (−26 °C). We used these measurements to calibrate a rock physics model to predict seismic velocity as a function of porosity, pressure, ice concentration and ice texture. Our results show that seismic velocity increases with ice concentration, and this increase is roughly 20 times higher for cementing ice than for granular ice. Our model can be used in future studies to predict how effective seismic methods may be for detecting and characterizing subsurface lunar ice deposits with varying ice properties and geologic complexity.