MNRAS 000,1{16 (2019) Preprint 12 December 2019 Compiled using MNRAS LATEX style file v3.0 Location, orbit and energy of a meteoroid impacting the Moon during the Lunar Eclipse of January 21, 2019 J.I. Zuluaga,1;3 M. Tangmatitham,2 P. Cuartas-Restrepo;1;3? J. Ospina,3 F. Pichardo,5 S.A. L´opez;3 K. Pe~na,5 J.M. Gaviria-Posada4 1Solar, Earth and Planetary Physics - SEAP, Institute of Physics, University of Antioquia, Calle 70 No. 52-21, Medell´ın, Colombia 2Department of Physics, Michigan Technological University, Houghton, MI, USA 3Sociedad Antioque~na de Astronom´ıa, CAMO & Orion groups, Medell´ın, Colombia 4Observatorio la Loma, V´ıaConcepci´on-San Vicente Ferrer, Colombia 5Sociedad Astron´omica Dominicana, Avenida M´aximo G´omez esquina C´esar Nicol´as Penson, Plaza de la Cultura, Santo Domingo, Rep´ublica Dominicana Accepted XXX. Received YYY; in original form ZZZ ABSTRACT During lunar eclipse of January 21, 2019 a meteoroid impacted the Moon producing a visible light flash. The impact was witnessed by casual observers offering an oppor- tunity to study the phenomenon from multiple geographical locations. We use images and videos collected by observers in 7 countries to estimate the location, impact pa- rameters (speed and incoming direction) and energy of the meteoroid. Using parallax, − +0:30 − +0:07 we achieve determining the impact location at lat. 29:43−0:21, lon. 67:89−0:09 and geo- centric distance as 356553 km. After devising and applying a photo-metric procedure for measuring flash standard magnitudes in multiple RGB images having different ex- posure times, we found that the flash, had an average G-magnitude hGi = 6:7 ± 0:3. We use gravitational ray tracing (GRT) to estimate the orbital properties and likely radiant of the impactor. We find that the meteoroid impacted the moon with a speed +7 of 14−6 km/s (70% C.L.) and at a shallow angle, θ < 38:2 degrees. Assuming a normal error for our estimated flash brightness, educated priors for the luminous efficiency and object density, and using the GRT-computed probability distributions of impact speed and incoming directions, we calculate posterior probability distributions for the kinetic energy (median Kmed = 0:8 kton), body mass (Mmed = 27 kg) and diameter (dmed = 29 cm), and crater size (Dmed = 9 m). If our assumptions are correct, the crater left by the impact could be detectable by prospecting lunar probes. These re- sults arose from a timely collaboration between professional and amateur astronomers which highlight the potential importance of citizen science in astronomy. Key words: Moon, meteorites, meteors, meteoroids, celestial mechanics. 1 INTRODUCTION (Madiedo et al. 2010) in Spain. According to MIDAS, one arXiv:1901.09573v5 [astro-ph.EP] 11 Dec 2019 meteoroid (hereafter L1-21J) impacted the darker side of the In January 21, 2019 the only total lunar eclipse of 2019 took eclipsed moon at 04:41:38 UTC(Madiedo et al. 2019). In the place. Thousands, if not millions of observers, followed the days after the eclipse, the Royal Observatory1 reported a event in America, north Africa and in most of Europe. As second flash just two minutes after L1-21J occurring on the usual, several amateur and professional observatories around western and much brighter limb of the eclipsed moon. To the world streamed the whole eclipse over the internet. the date of writing, however, this second flash has not been A few minutes after the beginning of the total phase of confirmed by other observers, and therefore, it could also be the eclipse, several sources on the internet claimed the ob- attributable to other effects, such as instrumental artefacts servation of a short light flash on the east side of the eclipsed or cosmic rays (see eg. Suggs et al. 2011, Suggs et al. 2014) moon. A few hours after, the flash was fully confirmed by Right after the confirmation by MIDAS of the impact, the Moon Impacts Detection and Analysis System, MIDAS ? Corresponding author: [email protected] 1 https://www.rmg.co.uk © 2019 The Authors 2 Zuluaga et al. several observers around the world reported the independent (∼ 1 hour) is 33%; the probability of observing exactly two detection of the light flash in their own footage. Although or more is 6%, etc. Naturally, most of those impacts will be lunar impacts are relatively common, the impact of Jan- very dim and hard to detect with small equipment. uary 21, 2019 is the first one to be detected simultaneously In recent years, improved optical and electronic astronom- by thousands of observers during a total lunar eclipse. This ical equipment and prospecting lunar satellites, have allowed offers unique opportunities to study this phenomena from the detection of hundreds of \fresh" impacts on the moon us- different geographical locations, and using different instru- ing two methods: 1) a local method, involving the repeated ments and independent methods from those used by lunar observation of the same portions of the lunar surface at dif- flash surveys (see Section2). ferent times, from prospecting satellites; and 2) a remote Here, we present a scientific analysis of the L1-21J event method, which relies on the observation of the short visible using observations gathered, independently, by amateur and light flashes produced during the impacts. professional astronomers, in Colombia, the Dominican Re- The NASA Lunar Reconnaissance Orbiter (LRO) has suc- public, USA, Canary Islands, Cape Verde, Czech Republic, cessfully tested the first method2. During a 6 years mission Austria, and Germany (see section3). First, we briefly re- (Keller et al. 2016) the LRO has taken high-resolution im- view what is known about impacts by small meteoroids on ages (down to 1 meter per pixel) of 70% of the Moon sur- the Moon (Section2). Then, we describe the instruments face, with almost 3% of the surface observed at least two and data we gather and analyse for this work (Section2). times. During that time, the spacecraft has detected signa- One of the most interesting characteristic of our approach, tures of hundreds of fresh impacts. The present resolution of is the numerical reconstruction of the meteoroid trajectory, LRO allows the detection craters as small as 10 m (Speyerer which is required to estimate the speed and the incident an- et al. 2016). LRO fresh impact signatures have been used for gle. For this purpose we use the novel Gravitational Ray calibrating the Moon cratering flux and to test theoretical Tracing (GRT) technique (Section5). Photometric analysis estimations of meteoroid fluxes on the Earth-Moon system of our footage provide us estimations of the total energy in- (Keller et al. 2016). volved in the impact (Section6); from there we can estimate Particularly famous are two impacts that were first ob- the posterior probability distribution (ppd) of the mass and served from the Earth and afterwards, their associated crater size of the impactor (Section7). The precise location of the discovered by LRO. The first one was a extremely bright im- impact and the crater diameter left by the event are also pact happening on March 17, 2013 (Suggs et al. 2014); the estimated. second one happened on September 11, 2013 and it was first identified by the MIDAS system Madiedo et al. 2014 and then observed by LRO (see below). In the last two decades, several observing systems were 2 OBSERVATION OF MOON IMPACTS designed and built to monitor the Moon, looking-for flash Impacts on the Earth-Moon system are relatively common events (Ortiz et al. 2000, 2002, 2006; Suggs et al. 2014; Ortiz (Sigismondi & Imponente 2000a,b; Neukum et al. 2001; et al. 2015; Madiedo et al. 2015a,b; Yanagisawa & Kisaichi Ivanov 2001, 2006; Gallant et al. 2009; Moorhead et al. 2017; 2002). The first lunar-flash monitoring program, MIDAS, Drolshagen et al. 2017 and Silber et al. 2018 and references was established almost two decades ago in Spain (Madiedo there in). Drolshagen et al.(2017) for instance (see their et al. 2010). During that time, MIDAS has detected a signif- Figure 5) estimate that ∼ 104 − 105 small, low-mass me- icant number of flashes on the Moon, and the data collected teoroids (. 0:1 m diameter, . 1 kg mass) enter into the have been used to study the population properties of ma- Earth's atmosphere per year (∼ 1 − 10 impact per hour). jor meteor showers (Madiedo et al. 2014; Ortiz et al. 2015; The Earth/Moon ratio of meteoroid fluxes is estimated to Madiedo et al. 2015a,b). MIDAS was the first of such moni- be 1.38 (Ivanov 2006). Therefore, the rate of impacts on the tor system confirming the L1-21J event. In 2006, the NASA Moon is on a similar order of magnitude. However, since our Marshall Space Flight Centre started their own monitoring satellite lacks a dense atmosphere, the effects of those im- program3. To the date, the NASA's system has indepen- pacts on its surface are more dramatic and easier to detect. dently detected hundreds of events and helped to constrain With the exception of the event described in the chroni- the rate of meteors falling onto the Moon and, in general, cles of Gervase of Canterbury in 1178 (Hartung 1993) (whose the density and flux of meteoroids around the Earth-Moon nature is still debated), the visual observation of impacts on system (Suggs et al. 2011, 2014). More recently, the NEO the Moon is not very common. Those impacts could be ob- Lunar Impacts and Optical TrAnsients, NELIOTA saw the served under three favourable conditions: 1) in the days close first light (Xilouris et al. 2018). To date, and after just a few to the new moon when the dark side is illuminated by the months of operations, at least 55 flashes have been observed planet shine, 2) far from the dark limb, close to first or last by the NELIOTA program.