By Paul Roggemans and Jean-Marie Biets
An overview is presented of the trajectory and orbit of the fireball. The orbit may be associated with an earlier identified fireball stream listed as the January nu Orionids (JNO#267).
A slow-moving fireball occurred on 2019 February 15 over Belgium at 20h09m UT at a perfect clear sky. The event was witnessed by many thousands of people that were out after an exceptional warm 15th of February. Most common descriptions were the slow appearance and a green color reported by many people. Luckily many meteor cameras are active in this region which could capture the event and allow reliable positional measurements.
Already at 20h25m UT, Casper ter Kuile shared a post in the CAMS BeNeLux Facebook group from an AstroForum published within 4 minutes after the appearance of the fireball. Many casual witnesses enjoyed the natural phenomenon. The camera data from all-sky stations and CAMS came early the next morning when the cameras ended the capture of the night.
An overview of the images has been given before: https://www.meteornews.net/2019/02/16/fireball-over-belgium-2019-february-15-20h09m-ut/
2 The trajectory
The fireball started close to the Belgian-French border, south-east of the Belgian city Mons at 90 km height in the atmosphere. The endpoint was just across the Belgian-Dutch border, between the Belgian city Zelzate and the Dutch city Terneuzen. The ground path of the fireball shown in Figure 1 is based on the CAMS network data calculated by Carl Johannink. The cameras of the CAMS network registered the begin of the fireball which wasn’t bright enough for the all-sky cameras. The all-sky data was analyzed and calculated by Pavel Spurný at Ondrejov, Czech Republic. The ground path as obtained from the all-sky cameras differs slightly from the result obtained from the CAMS data. In Figure 2 the path according to CAMS is shown in white, the path according to the all-sky data is shown in yellow. The all-sky cameras registered the fireball from where it got bright enough, then at 78.8 km height in the atmosphere.
Table 1 – The trajectory data of the fireball of 2019 February 15, 20h09m UT, for the all-sky data calculated by Pavel Spurný and the CAMS data calculated by Carl Johannink.
|λb (°)||4.0428 ± 0.0006||4.0708 ± 0.0001|
|φb (°)||50.5319 ± 0.0003||50.3757 ± 0.0001|
|λe (°)||3.8162 ± 0.0006||3.8421 ± 0.0001|
|φe (°)||51.2293 ± 0.0002||51.2324 ± 0.0001|
The all-sky data was worked out in the Czech Republic based on the images from Wilderen, Oostkapelle, Ermelo and Borne. Jean-Marie Biets et al. (2019) concluded in their report that the accuracy of the result is insufficient for further scientific work. The cause mentioned by the authors is the too poor quality of the optics. Pavel Spurný has explained at several occasions at which details amateurs need to pay more attention if they want their data to be of scientific use. For instance, at the IMC in June 2016 at Egmont, the Netherlands, a long evening session was spent entirely to this topic by Dr. Pavel Spurný.
In this case there is no indication that anything survived the transit through the atmosphere, but if this had been the case the close-up of the difference between the ending points projected on the ground between CAMS and the All-sky, shown in Figure 2 gives an idea about the consequences to locate a possible strew field to search for meteorites.
However, it can be much worse for the accuracy. Figure 3 shows the trajectory obtained by the IMO (https://fireballs.imo.net/members/imo_view/event/2019/741?org=imo) based on casual witness reports. This path is so far away from the reality, a huge distance in kilometers, that it is completely of no use. Some people still claim this kind of trajectories are of scientific use, suggesting this is a valid alternative when no camera data is available. Also, for previous fireball events over the BeNeLux these casual reports produced ground plots far away from reality. It can be fun and a nice way to keep people busy about fireballs for outreach and educational purposes. However, these casual witness reports are absolutely no alternative for camera networks. If we want to learn anything about fireball events, we need good quality and well calibrated cameras. For this reason, we never use such casual witness reports. This fireball has also been registered by the FRIPON network, unfortunately no results were yet available at the moment this report was written.
3 The orbit
The orbit based on the BeNeLux CAMS network was calculated by Carl Johannink, the orbit based on the all-sky data was calculated by Dr. Pavel Spurný. The results are listed in Table 2.
Table 2 – The trajectory data of the fireball of 2019 February 15, 20h09m UT, for the all-sky data calculated by Pavel Spurný and the CAMS data calculated by Carl Johannink.
|αꝏ (°)||101.76 ± 0.05||99.11 ± 0.01|
|δꝏ (°)||-7.38 ± 0.02||-6.64 ± 0.01|
|vꝏ km/s||15.61 ± 0.03||15.64 ± 0.00|
|a (AU)||1.987 ± 0.003||2.1|
|e (AU)||0.5209 ± 0.0007||0.5472 ± 0.0003|
|q (AU)||0.9520 ± 0.0002||0.9542 ± 0.00003|
|i (°)||11.44 ± 0.02||11.227 ± 0.009|
|ω (°)||25.56 ± 0.06||25.233 ± 0.01|
|Ω (°)||146.5987 ± 0.0000||146.5914 ± 0.0000|
First, no meteor shower association could be made. The meteor shower association tool which combines three orbit similarity criteria used for the case studies of meteor streams based on orbit data (Roggemans, 2019) resulted in a positive match for both the CAMS and the all-sky data orbits compared with all orbits listed in the IAU Meteor Data Center (https://www.ta3.sk/IAUC22DB/MDC2007/index.php). For the CAMS orbit a similarity with acceptable discrimination values was found with a shower named January nu Orionids (JNO#267), with D-criteria DSH = 0.19, DD = 0.078 and DH = 0.169. For the all-sky data the association with this shower had DSH = 0.19, DD = 0.075 and DH = 0.17.
This shower has been identified by Dr. A. K. Terentjeva (1989) in a study of complexes of large meteor bodies. The data for this meteor shower has been listed in Table 3. The large difference in radiant position may mask possible shower association but is normal for ecliptical or nearly ecliptical fireball showers with slow moving meteors. In her original publication Dr. A. K. Terentjeva identified this shower as the Mu-Orionids active between 1 January until 4 February. However, this activity period is only indicative and does not exclude orbital associations beyond this period. The IAU working list mentions 2003 AC23 as possible asteroidal parent body. Both the pre-atmospheric velocity vꝏ (= 16.4 km/s) and the geocentric velocity vg (= 12 km/s) agree very well with the CAMS data.
The all-sky data had a second match with DSH = 0.18, DD = 0.093 and DH = 0.18. with the meteor shower chi2 Orionids (CHO#990) based on 24 orbits and listed in the IAU working list of meteor showers pro tempore. This shower just scores beyond the upper limit for DD (= 0.105) with 0.112 for the CAMS orbit. The shower orbit is listed in Table 3. The activity of this shower is more than one month later than our fireball and may represent a similarity by pure chance. The large difference in the ascending node and argument of perihelion is not a problem if we look at the length of perihelion Π.
Table 3 – The orbital elements for the January nu Orionids (JNO#267) and the chi2 Orionids (CHO#990).
Unfortunately, the reference listed as “Amaral et al., 2018, WGN to be sub.” Seems not to exist as never anything was submitted for publication. This way no sources can be checked. It is somehow a mystery how this information got into the IAU Meteor Data Center and who decided about the shower name and data verification.
The trajectory and orbit for the fireball of 2019 February 15, 20h09m UT could be calculated based on CAMS BeNeLux data and all-sky data. The orbit may be associated with an earlier identified fireball stream listed as January nu Orionids (JNO#267) another possible association with chi2 Orionids (CHO#990) is less likely and uncertain because the references cannot be verified.
The authors thank Pavel Spurný and Carl Johannink for their calculations on this fireball images.
Biets J.-M., Johannink C. and Spurný P. (2019). “De vuurbol van 15 februari 2019”. Radiant, 41, 22–25.
Roggemans p., Johannink C. and Cambell-Burns P. (2019). “October Ursae Majorids (OCU#333)”. eMetN, 4, 55–64.
Terentjeva A. K. (1989). “Fireball streams”. WGN, Journal of the International Meteor Organization, 17, 242–245.