NELIOTA: Methods, statistics, and results for meteoroids impacting the Moon

Abstract

Context. This paper contains the results from the first 30 months of the NELIOTA project for impacts of Near-Earth Objects/meteoroids on the lunar surface. Our analysis on the statistics concerning the efficiency of the campaign and the parameters of the projectiles and the impacts is presented. Aims. The parameters of the lunar impact flashes based on simultaneous observations in two wavelength bands are used to estimate the distributions of the masses, sizes and frequency of the impactors. These statistics can be used both in space engineering and science. Methods. The photometric fluxes of the flashes are measured using aperture photometry and their apparent magnitudes are calculated using standard stars. Assuming that the flashes follow a black body law of irradiation, the temperatures can be derived analytically, while the parameters of the projectiles are estimated using fair assumptions on their velocity and luminous efficiency of the impacts. Results. 79 lunar impact flashes have been observed with the 1.2 m Kryoneri telescope in Greece. The masses of the meteoroids range between 0.7 g and 8 kg and their respective sizes between 1-20 cm depending on their assumed density, impact velocity, and luminous efficiency. We find a strong correlation between the observed magnitudes of the flashes and the masses of the meteoroids. Moreover, an empirical relation between the emitted energies of each band has been derived allowing the estimation of the physical parameters of the meteoroids that produce low energy impact flashes. Conclusions. The NELIOTA project has so far the highest detection rate and the faintest limiting magnitude for lunar impacts compared to other ongoing programs. Based on the impact frequency distribution on Moon, we estimate that sporadic meteoroids with typical masses less than 100 g and sizes less than 5 cm enter the mesosphere of the Earth with a rate ∼ 108 meteoroids hr −1 and also impact Moon with a rate of ∼ 8 meteoroids hr −1 .

Meteoroids as One of the Sources for Exosphere Formation on Airless Bodies in the Inner Solar System

“…Early observations, focused on maximising the impact detection rate, were preferentially carried out during meteor showers. These were followed by surveys where observations took place regularly under favourable lunar observing conditions, showing that the occurence of flashes is indeed correlated with showers (Suggs et al 2014;Liakos et al 2020). After the impact of a kg-sized meteoroid near the lunar terminator two dust clouds with typical expansion velocities of 0.1 and 3 km s −1 were observed (Berezhnoy et al 2019).…”

Impacts on the Moon: Analysis methods and size distribution of impactors

“…A.5), duration and the calibrated peak magnitudes in R and I bands. Unfortunately, as it is derived by Xilouris et al (2018) and Liakos et al (2020), the reported magnitudes and errors on the NELIOTA database are approximate, while some selenographic coordinates are possibly reported incorrectly (swapped longitude and latitude).…”

“…In this work, for the flashes with numbers 1-80 we use the published magnitudes and selenographic coordinates (Xilouris et al, 2018;Liakos et al, 2020), while for the rest (81-112) we use the data as reported on the website. As we will see later, we use our method and re-compute the selenographic coordinates (Tab.…”

“…At each iteration, a temperature value is derived from a new set of R and I that are extracted from Gaussian distributions centred on the nominal R and I values of the LIF and standard deviations equal to the magnitude errors given by NELIOTA and/or literature (Liakos et al, 2020). It has been stated that the NELIOTA R and I magnitude values and errors, as presented in the web-page, are an approximation and therefore when possible we use the published ones (Xilouris et al, 2018;Liakos et al, 2020).…”

Analysis of the First Optical Detection of a Meteoroidal Impact on the Lunar Surface Recorded from Brazil

“…Video monitoring for flashes initially took place about 25 years ago (e.g., [6]), and they were first observed in the 1999 Leonids activity [7][8][9]. Lately, observations for flash detection have been conducted systematically [10][11][12].…”