SPMN160819 superbolide: reconstructing its atmospheric trajectory by matching ground-based recordings and satellite data

1. Introduction

Extremely bright fireballs are rarely recorded events that provide valuable information for meteor science. From the study of these luminous phases is obtained valuable information about the meteoroids physical properties and their origin in the Solar System. Meter-sized meteoroids are consequence of the continuous decay of asteroids and comets, their main parent bodies [1]. The recovery of new meteorites and the study of the dynamic association with comets, asteroids or planetary bodies gives new clues on the physical processes delivering space rocks to Earth [2, 3].

Fireball monitoring tasks differ from most other types of astronomical observations since these events cannot be predicted either in time or direction. For this reason, it is necessary to monitor the sky with full-time coverage. That is the goal of multiple stations fireball systems. However, given the heterogeneous distribution of such initiatives around the globe, some events are unnoticed, and others partially recorded. This is particularly truth for superbolides produced by m-sized bolides that are hitting the atmosphere few times every year. To increase our data on the atmospheric behaviour and the origin of these elusive superbolides, satellite records can play a crucial role in the reconstruction of the trajectory.

2. Methodology

The astrometric reduction of meteors and fireballs involves a complex and tedious process that generally requires many manual tasks. To streamline the process, we have developed a software called 3D Fireball Trajectory and Orbital Calculator (3D-FireTOC), an automatic Python code for automatic detection, trajectory reconstruction of meteors and heliocentric orbit computation from CCD recordings. This software has been made in the framework of the Spanish Meteor and Fireball Network (SPMN) activities [4]. For the reconstruction of the atmospheric trajectory, we have implemented the method proposed by [5]. The distortion due to the wide-angle lens is modelled by a quadratic expression, which can be solved iteratively by combination of a simplex algorithm and the least squares method [6]. For the astrometric process, we applied corrections by light aberration, refraction, zenith attraction, diurnal aberration and atmospheric extinction.

We implemented the method proposed by [7] for determining fireball fates using α−β criterion. Thanks to the characterization of the atmospheric flight, the pre-atmospheric and final mass can be computed. The orbital parameters are computed from radiant and velocity data and compared with our previous SPMN software and the widely distributed spreadsheet done by Langbroek [8].

3. Case Study: Superbolide SPMN150819

On August 16, 2019, a very bright superbolide catalogued as SPMN160819 event occurred (see Table 1). It was an event of considerable importance due to its magnitude that, unfortunately, was only partially recorded from the Eivissa station of the SPMN network. Given the low resolution of these recordings due to the long range of almost 500 km, we used the peak brightness coordinates measured by the Center for Near Earth Object Studies of NASA to complete the reduction of this event.

Table 1: Stations involved in the fireball detection. *Casual observation points.

From Eivissa video recording, in which the Moon appears at a similar altitude, the superbolide was found to be more luminous than the Moon. It allowed us to quantify its absolute magnitude in −16.5 ± 0.5, in agreement with a detection from space. Due to the enormous distance to the Eivissa station, the superbolide was first detected there when ablation was severe at a height of 48.0 km and ended at 28.5 km. The main astrometry was performed using Eivissa station data, located 480 km from the event, which may explain the low height obtained.

The result for the pre-atmospheric velocity has been 16.6 km/s and the terminal velocity 11.8 km/s. Assuming a mean value of ordinary chondrite’s density of 2.7 g/cm³ [9], the α−β criterion shows that it will probably produce a meteorite. The pre-atmospheric meteoroid mass was estimated to be ~1100 kg with an initial size of ~1 m. The terminal computed mass is ~1 kg, which is in good agreement with previous studied bolides [10]. Table 2 compiles the computed values. Radiant and inferred orbital elements reveal that it was a sporadic event.

                  

Table 2: (Top) Geocentric and heliocentric radiant and velocities. (Bottom) Orbital elements. 

Figure 1: Atmospheric trajectory based on the records from Eivissa (orange), Sardinia (green) and Costa Brava (purple).

4. Conclusions

We reconstructed the trajectory of the SPMN160819 event using the bolide peak brightness obtained from satellite data, a video recording from Eivissa SPMN station, and a casual picture of its persistent trail. The event exemplifies the ability of our software to use Earth-observation satellite data and ground based observations for obtaining the trajectory and orbit of a distant bolide. Even when the number of stations was limited, the atmospheric flight and the terminal mass were computed, indicating that the event was produced by a meteorite-dropper candidate. Unfortunately, our results indicate that any surviving meteorite fell into the Mediterranean Sea.

Acknowledgements

The authors acknowledge financial support from the Spanish Ministry (PGC2018-097374-B-I00, PI: JMTR). We also thank to the casual observers of the event for kindly providing their bolide records: Claudio Porcu and Quico Terradelles i Palau.

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