Moon Watch: Continuous Monitoring of the Lunar Surface to Constrain Current Impact Flux

Though very large impacts are rare on the Moon today, there is evidence that small impacts occur regularly across the lunar surface. The LRO Camera (LROC) has measured an impact flux higher than anticipated and observed secondary cratering processes that churn the top two cm of regolith significantly faster than previous models. These measurements altered our understanding of the current impactor flux with potentially significant ramifications for understanding lunar surface model ages and robotic/human landing safety hazards. A method for continuing to track current lunar impact flux is to monitor for impact flashes. When a hypervelocity projectile impacts a target, a light flash is produced at the moment of first contact. Time-resolved light intensity curves can be used to search for flashes and determine the starting conditions of the observed impacts. It is possible to monitor impact flashes from Earth, but these observations are complicated by atmospheric interference, the ability of the instrumentation to spatially resolve events at great distances, and limitations in observable area to the nearside and during certain lunar phases. Placing an impact flash monitoring station in cis-lunar space could mitigate many of these limitations and provide estimates for current impact flux and distribution.

Moon Watch is a mission concept to monitor flashes from lunar orbit that includes two main techniques: flash detection and measurement using a high-speed multi-band radiometer and flash locality determination using a combination of wide-field and high-resolution cameras. The radiometer provides continuous monitoring by staring at the surface of the Moon. When a flash occurs, the rapid rise in intensity will trigger the cameras. A wide-view camera would cover the full lunar disk and used to track general location where the impact occurs; it could be accommodated alongside the radiometer on a small satellite. If a larger platform is available, additional high-resolution images may be taken to provide operationally useful locations to orbiting cameras for follow-up observations. These images would require a narrow-angle high-speed camera (or, perhaps an array of narrow-angle cameras).