The first observations to determine the temperature of a lunar impact flash and its evolution

Abstract

We report the first observations on 25 March 2015 of a flash produced by the impact of a meteoroid on the lunar surface and recorded both in the near-infrared and in the visible. These observations provided the temperature of this telescopic lunar impact flash (Madiedo and Ortiz 2016, 2018). Recently, during the refereeing process of our manuscript, Bonanos et al. (2018) used the same technique but with NELIOTA data from February 2017 to produce the first refereed publication of a temperature measurement. The flash exhibited a peak magnitude of 5.1 ± 0.3 in the near-infrared I band and 7.3 ± 0.2 in the visible, and the total duration of the event in these bands was 0.20 and 0.18 s, respectively. The origin of the meteoroid was investigated, and we inferred that the most likely scenario is that the impactor that belonged to the sporadic background. The analysis of this event has provided for the first time an estimation of the emission efficiency in the near-infrared ηI for sporadic meteoroids impacting the Moon. We have determined that this efficiency is around 56 per cent higher than in the visible band and we have found a maximum impact plume temperature of ∼4000 K at the initial phase followed by temperatures of around 3200 K after the peak brightness. The size of the crater produced as a consequence of this impact is also calculated.