Short note on what appears to have been a 2024 outburst of epsilon-Ursae-Minorids (IAU#1044)

By: Peter Jenniskens (SETI Institute), Carl Johannink (CAMS BeNeLux), Nick Moskovitz (Lowell Observatory), and Andy Howell (CAMS Florida)

Abstract: A meteor outburst with a radiant in Ursa Minor was detected by low-light level video cameras of the Global Meteor Network and by Belarusian and Ukranian meteor camera networks on September 23–25, 2024. Here, we report on the results from the CAMS network and discuss the possible association with the epsilon-Ursae-Minorids outburst observed in 2019. If this is the same stream, a return of the shower is expected in 2025, and again in 2030/2031.

Introduction

On October 1, 2024, Vida & Segon (2024) and Harachka et al. (2024) independently reported on the detection of  a possible new shower with a radiant in Ursa Minor. The shower was rich in bright meteors. A possible parent body was proposed as asteroid 2021 HK12. According to Vida & Segon, this was not a return of the epsilon-Ursae-Minorids (IAU#1044), detected as an outburst in 2019 by Sato (2020), even though the time of maximum and entry speed were much the same. Here, we briefly look into whether or not both showers can be related.

Methods

The CAMS camera network detected this event as a compact shower with 1 triangulation in CAMS Florida, 9 triangulations in CAMS BeNeLux and 6 triangulations in LO-CAMS. Because both CAMS BeNeLux and LO-CAMS deploy many RMS cameras among the CAMS Watec cameras, these results are not fully independent. Only three of the meteors are independent triangulations from the Global Meteor Network results (Vida & Segon, 2024). All were triangulated with the CAMS software.

Results

The shower activity ranged from 2024 September 22 – 25, corresponding to solar longitude 180.0 to 182.5º (Equinox J2000.0), with most activity (N = 10) during 180.9–182.2º .  Median orbital elements are given in Table 1, and are in good agreement with earlier reported results.

Table 1 – The median orbital elements (Equinox J2000.0) of the 2024 shower with a radiant in Ursa Minor.

		2024 Vida & Segon (2024)	2024 Harachka et al. (2024)	2024 CAMS	EPU: 2019 (Sato 2020)	EPU: 2019 (Shiba 2022)	2021 HK12
	λʘ (°)	181.8 ± 0.4	181.93 ± 0.12	181.44 ± 0.70	182	181.9	187.08
	αg (°)	238.27 ± 5.4	238.37 ± 1.32	241.3 ± 3.6	252	255.0	243.8
	δg (°)	+77.26 ± 1.2	+77.35 ± 0.15	+77.3 ± 1.2	+83	+82.6	+72.1
	vg (km/s)	32.0 ± 1.2	31.08 ± 1.12	31.9 ± 1.4	33	33.6	28.1
	λ – λʘ (°)	296.63	-.-	296.1 ± 4.0	276.3	-.-	-.-
	β (°)	+75.72	-.-	+76.2 ± 1.0	+73.5	-.-	-.-
	a (AU)	2.34 ± 0.16	2.73 ± 0.41	3.51	2.5	2.756	3.286
	q (AU)	0.994 ± 0.03	0.996 ± 0.001	0.997 ± 0.002	1.00	1.003	1.038
	e	0.68 ± 0.03	0.629 ± 0.055	0.717 ± 0.068	0.61	0.636	0.684
	ω (°)	169 ± 2	168.74 ± 0.68	169.8 ± 1.8	178.3	178.7	168.8
	Ω (°)	181.8 ± 0.4	181.93 ± 0.12	181.4 ± 0.7	182.0	181.9	187.1
	i (°)	53.9 ± 2.4	52.8 ± 1.4	53.7 ± 2.0	57.6	57.8	47.0
	Π (°)	350.8	350.7	351.2 ± 1.7	360.3	360.6	355.9
	Tj	-.-	-.-	2.18 ± 0.37	-.-	-.-	2.37
	N	31	4	16	13	10	-.-

 

Discussion

The epsilon-Ursae-Minorid shower is not included in the Atlas of Jenniskens (2023). That appears to be an omission. Looking back at the past 2007–2020 SonotaCo, EDMOND, and CAMS data shows a distinct shower between solar longitudes 178 and 184 degrees, centered on a radiant at ecliptic coordinates 271.7, +73.9 degrees and Vg = 33.6 km/s. The number of meteors per year, starting in 2007 are: 4, 0, 0, 0, 1, 0 11, 1, 1, 2, 1, 1, 32, 1. Hence, the epsilon-Ursae-Minorids shower appears to be episodic and was in outburst in (2007,) 2013, and 2019. A periodicity of 6.0 ± 0.4 years is suggested. The year 2024 would fit in this sequence if the periodicity is about 5.7 years (semi-major axis a ~ 3.19 AU), or if the concentration of dust along the orbit is wide enough dispersed to give activity at Earth in both 2024 and 2025.

The 2024 outburst was at a sun-centered ecliptic radiant of 296.1 ±4.0 , +76.2 ± 1.0 degrees  around 181.4º (Table 1). In 2007, the radiant was at about 270.6, +74.1 degrees around solar longitude ~180.5º, while the radiant was centered at 264.1, +73.9 degrees around 181.1º in 2013, and at 271.9, +73.8 degrees around 181.5º in 2019. That observed variation in ecliptic longitude of past shower radiants suggests that the 2024 outburst can be a return of the epsilon-Ursae-Minorids.

Asteroid 2021 HK12, identified by Vida & Segon (2024) as a possible parent body, appears to be a fair match to the stream. The longitude of perihelion is in between that of the epsilon-Ursae-Minorids and the 2024 shower. The asteroid has a Tisserand parameter with respect to Jupiter in the Jupiter-family comet range and has a semi-major axis of 3.286 AU (corresponding to an orbital period P = 5.96 years).

The observed meteoroids must have been ejected some time ago given the significant difference in inclination between the current parent body orbit and that of the stream. If so, then the dust is likely not that of recent dust ejecta, but rather dust from older ejecta accumulated in the 2:1 mean-motion resonance with Jupiter. That would predict a more regular pattern of outbursts with the period of the resonance (6 y). In that case, we may expect to see this shower again in 2025. And if it does, the shower is likely to return also in 2030 and/or 2031.

Acknowledgements: While only three of the CAMS networks captured this September 2024 outburst, the detection was made possible by the concerted effort of all CAMS network and station operators as well as by efforts from Dave Samuels and Steve Rau, who continue to maintain the CAMS networks.

References

Harachka Y., Mikulich A., Morozov K., Angelsky A. (2024). Possible new meteor shower in Ursa Minor. eMeteornews 9, 395–396.

Jenniskens P. (2023). Atlas of Earth’s Meteor Showers, Amsterdam: Elsevier, 838 pp.

Sato M. (2020). Epsilon Ursae Minorid shower 2019. CBET 4860. D. W. E. Green (ed.), 1pp.

Shiba Y. (2022). Jupiter family meteor showers by SonotaCo network observations. JIMO 50, 38–61.

Vida D., Segon D. (2024). New meteor shower M2024-S1 in Ursa minor. CBET 5452. D. W. E. Green (ed.), 1 pp.