LRO-LAMP detection of geologically young craters within lunar permanently shaded regions

The upper 25-100 nm of the lunar regolith within the permanently shaded regions (PSRs) of the Moon has been demonstrated to have significantly higher surface porosity than the average lunar regolith by observations that the Lyman-α albedo measured by the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) is lower in the PSRs than the surrounding region. We find that two areas within the lunar south polar PSRs have significantly brighter Lyman-α albedos and correlate with the ejecta blankets of two small craters (<2 km diameter). This higher albedo is likely due to the ejecta blankets having significantly lower surface porosity than the surrounding PSRs. Furthermore, the ejecta blankets have much higher Circular Polarization Ratios (CPR), as measured by LRO Mini-RF, indicating increased surface roughness compared to the surrounding terrain. These combined observations suggest the detection of two craters that are very young on geologic timescales. From these observations we derive age limits for the two craters of 7-420 million years (Myr) based on dust transport processes and the radar brightness of the disconnected halos of the ejecta blankets.