Lunar impact flashes: analysis methods

Lunar impact flashes: analysis methods

Munaibari⁽¹⁾, R. Larson⁽²⁾, C. Avdellidou⁽¹⁾, M. Delbo⁽¹⁾, J. Vaubaillon⁽³⁾, P. Hayne⁽²⁾, D. Sheward⁽⁴⁾, A. Cook⁽⁴⁾

(1)Laboratoire Lagrange, Observatoire de la Côte d’Azur, UCA, France

(2)University of Colorado, USA

(3)IMCCE, Observatoire de Paris, France

(4)Aberystwyth University, UK

contact: chrysa.avdellidou@oca.eu

Abstract

We present our complete method to analyse lunar impact flashes; from the identification of the selenographic coordinates to the estimation of masses and sizes of the meteoroids. For this work we used archival data from the ESA-funded NELIOTA survey and we report an updated catalogue of the impact coordinates and link to meteoroid streams. This project is in the framework of our project Flash!, which aims to detect impacts in real time during the observations, identify the lunar coordinates and attempt the discovery of the fresh craters using LRO data. The scientific problem is to establish a link between the diameter of the meteoroid impactor and the diameter of the impact crater quantifying this scaling with live impact observations.

Selenographic coordinates and link to meteor streams

In this work, we exploit the publicly available datafrom NELIOTA (1,2), an ESA-funded survey at the National Observatory ofAthens (NOA). The first step is to identify the impact coordinates on the Moon. Using the method described by Larson et al. EPSC 2019 we have discovered that several impact locations given by the NELIOTA team are inaccurate and in some cases are off by 10s of degrees.

The importance ofaccurately locating the position of an impact flashcomes for the fact that it is needed to perform theprocess of linking the impactor to its source and this is crucial to identify the originof the impactor. In this work we evolve from our previous studies (3) and we investigate also the possibility an impactor to originate from the sporadic population and not only from meteoroid streams.

 

Masses and Sizes of the meteoroids

According to previous studies (2,3), an impact flashis treated as a black body whose spectral energy distribution is described by Planck’s law. Using the flash magnitudes in R and I bands we estimate temperature values as described with details in (3).

The mass of an impactor can be derived from its kinetic energy (KE). To calculate the impact KE it is necessary to measure the luminous energy E_Lum from the telescopic observations, which is just asmall fraction, η, of the KE.

In order to be able to estimate the kinetic energyof an impactor, it is essential to know the velocityat which it impacted onto the lunar surface. Thisvelocity is obtained by linking the impactor to its source, either a known meteoroid stream or the sporadic background population. In the case of streams, the velocity of their meteoroids is known.Once the link is established, the velocity of an impactor is easily computed by finding the differencebetween the velocity of the meteor shower’s particles and that of the Moon at the time of the impact.

Assuming a spherical shape for the impactors andwith the estimation of their masses we can now estimate their sizes. In this work, we utilised th e bulk densities that have been reported (4) for the fragments of some ofthe shower streams by assigning impactors with thebulk density of the meteor showers we found to betheir plausible sources. Finally, we construct the size frequency distribution with a slope of -2.48 as shown in Fig.1 and is comparable with the NASA survey (5).

 

 

 

Acknowledgements

This work was supported by the ProgrammeNational de Planetologie  (PNP), France  of CNRS/INSU, co-funded by CNES, France and bythe program "Flash!" supported by Crédits Scientifiques Incitatifs (CSI), France of the UniversitéNice Sophia Antipolis. This work has made use ofdata from the European Space Agency (ESA) NELIOTA project. We thank the EUR Spectrum for supporting Mr. Munaibari with a 3-month UCA Master Scholarship to perform this masterthesis.

References

[1] E. Xirouris, et al. A&A,619, A141 (2018).

[2] A. Z. Bonanos, et al.  A&A, 612 (2018)

[3] C. Avdellidou & J. Vaubaillon. MNRAS, 484(4):5212–5222 (2019).

[4] P. B. Babadzhanov & G. I. Kokhirova., A&A, 495:353–358(2009).

[5] R. Suggs et al. Icarus, 238, 23 (2014).