This is a CBET telegram on a new meteor shower from comet 46P/Wirtanen. This comet was the initial destination for ESA's Rosetta mission before a launch delay changed the destination to 67P.
CBET 5324:
P. Jenniskens, SETI Institute and NASA Ames Research Center, reports that a predicted earth encounter with 1974 ejecta from comet 46P (cf. Vaubaillon et al. 2023, A.Ap, in press; website URL /https://arxiv.org/abs/2312.02636) was detected as a new meteor shower in the southern hemisphere on 2023 Dec. 12. Prior to this detection, comet 46P was not known as the parent body of a meteor shower. Vaubaillon et al. used several different dynamical models to predict a radiant near the stars lambda^1 and lambda^2 Scl with coordinates in the range R.A. = 7.3 to 9.2 deg, Decl. = -38.5 to -43.0 deg, and geocentric velocity 9.8 to 10.3 km/s, with a time of maximum expected in the range Dec. 12d09h to Dec. 13d06h UTC, with most models in the range Dec. 12d09h.5 to 11h.6 UTC. The proposed name for the new shower was lambda-Sculptorids (with code LSC). Leading up to the predicted peak, CAMS Chile detected a meteor from R.A. = 4.6 +/- 0.5 deg, Decl. = -36.4 +/- 0.9 deg, with geocentric velocity 8.6 +/- 0.1 km/s at solar longitude 259.402 deg (equinox J2000.0); corresponding orbital elements were a = 4.1 AU, q = 0.968 AU, e = 0.766, i = 7.6 deg, Peri. = 343.7 deg, and Node = 79.4 deg.
The first indication of a meteor outburst was reported by H. Sugimoto (cf. website URL https://www.iprmo.org/flash/gem-2023.html), who detected a sharp increase in radio forward meteor reflections from 41 stations starting at solar longitude 259.7 deg (Dec. 12d09h UTC). Rates peaked at solar longitude 259.9 deg (Dec. 12d13h UTC). For an assumed meteor-magnitude distribution index, the calculated equivalent peak visual zenith hourly rate (ZHR) was given as 120 meteors/hr. Subsequently, J. Scott (University of Otago, New Zealand), from calculations by D. Vida (Global Meteor Network), reported the detection of a cluster of 8 meteors from low-light video triangulations with a radiant centered on R.A. = 7.9 +/- 1.1, Decl. = -38.8+/- 0.3 deg and geocentric velocity 10.2 +/- 0.4 km/s (standard error given) during the solar longitude interval 259.76-259.96 deg, centered on 259.86 +/- 0.02 deg (see map at website URL http://cams.seti.org/FDL/index-NZ.html for the date 2023 Dec. 13). Corresponding median orbital elements are a = 2.93 AU, q = 0.9846 +/- 0.0002 AU, e = 0.662 +/- 0.084, i = 9.6 +/- 0.9 deg, Peri. = 0.1 +/- 1.4 deg, Node = 79.89 +/- 0.07 deg (standard deviations given here). This confirms that the observed peak of radio forward reflections was due to the meteors of comet 46P, but the actual peak ZHR for a visual observer was likely lower.
Copyright 2023 CBAT - 2023-December-13 (CBET 5324) - Daniel W.E. Green
