The Resultant Craters from Lunar Impact Flashes

Abstract

IntroductionImpacts are one of the most destructive processes in the solar system, and impact craters have been identified on almost every type of solar system body. The lunar surface is covered in craters ranging from 2500 km in diameter, down to sub-millimetre scale. Lunar impact flashes (LIF) are caused by incandescence during an impact, and can be observed by ground based telescopes. Over 650 LIFs have been observed within literature [1,2,3], but despite this large volume of data, only 3 freshly formed craters with documented LIF have been located previous to this work. Such craters are important, as they serve as ground truth data for both the refinement of the luminous efficiency, η, typically taken as between 10-2 and 10-4, and for analysing which crater scaling law is most accurate at the scale of the observed craters. MethodPyNAPLE is software we developed to locate the resultant crater within Lunar epoch, of an observed LIF [4]. Using the >650 LIFs available in literature, we applied constraints to filter out the unconfirmed events, and to prioritise the higher energy events, which had the highest probability of being detected with PyNAPLE. In total, this left 22 LIFs to be processed with PyNAPLE. ResultsAfter processing the 22 LIF events, there were sufficient LROC images to locate the freshly formed craters for six new events, as well as the three already identified within literature[4,5,6]. For one of these events, two candidate craters were found. Additionally, two unlinked craters were located during the search, however comparing the formation window of these craters to the database of LIFs, no candidate formation events were identified. A selection of six of these craters is shown in Fig. 1. Figure 1: Six of the craters located from LIF observations by PyNAPLE. Analysis & DiscussionFor each of the 9 craters with known formation event, the likely parent meteoroid stream for each event can be obtained by comparing the LIF location to the meteoroid streams that were active and visible to the impacting location at the time of impact. Identification of the parent stream gives an approximate value for the impactors velocity, impacting angle, and projectile density.Using the calibrated brightness of each flash, a value for the luminous energy, Elum, can be obtained for each event. Using an estimate for η, the total kinetic energy of the impactor for each event can also be caluculated, KE = Elum / η.The crater scaling laws are several equations which all attempt to relate the kinetic energy of an impactor to the rim-to-rim diameter of the formed crater. As they were mostly derived from explosive tests, their accuracy at the