Lunar Impact Flashes and their Resultant Craters 

Impact craters have been identified on almost every type of celestial body, and are among the most destructive processes. The lunar surface is covered in craters ranging from 2500km in diameter, down to sub-millimetre scale, and >600 lunar impact flash (LIF) events have been observed by ground based telescopes, detecting the generated light. Despite this large volume of data, previously only three freshly formed craters had been both located within LROC imagery, and have the forming LIF documented.Using PyNAPLE (Sheward et al., 2022) - software which locates fresh craters from the selenographic latitude, longitude, and epoch of a LIF - a search was performed upon the 22 most energetic LIFs within literature. For completeness, this included the three LIF events with already identified craters. There were sufficient LROC images to locate six new freshly formed craters, in addition to the three already identified. For these nine events, the likely parent meteoroid stream for each event is identified to constrain the velocity, impact geometry, and impactor properties. From this, the pre-impact kinetic energy could be obtained from an estimation for the luminous efficiency, and the luminous energy released by the LIF. Furthermore, using the crater scaling laws from Melosh (1989), both the predicted crater size from the kinetic energy, and the predicted energy from the observed crater size, could be calculated for each event. From this, it was found that the predicted crater diameter was consistently larger than the observed crater. While there are several factors that could contribute to this, the single most likely factor is the poorly constrained luminous efficiency. Under this assumption, a more accurate value for the luminous efficiency can be calculated using the observed craters. Using a rearrangement of the crater scaling laws, with the kinetic energy equation, and luminous efficiency, η = Elum/Ek where Elum is the energy released by the LIF, and Ek is the kinetic energy. After outlier removal and meteoroid stream identification, this produces an average value of η=0.0171324. While this is slightly larger than the typically used values of between 10−2 and 10−4, the difference is not drastic. References Melosh, H. J. (1989). Impact cratering : a geologic process.Sheward, D. et al (2022). MNRAS, 514(3):4320–4328