Modelling the 2022 τ-Herculid outburst

Abstract

The $τ$-Herculids (IAU shower number #61 TAH) is a minor meteor shower associated with comet 73P/Schwassmann-Wachmann 3, a Jupiter-Family comet that disintegrated into several fragments in 1995. As a consequence of the nucleus break-up, possible increased meteor rates were predicted for 2022. On May 30-31, observation networks around the world reported two distinct peaks of TAH activity, around solar longitudes 69.02° and 69.42°. This work examines the encounter conditions of the Earth with meteoroids ejected from 73P during the splitting event and on previous perihelion passages. Numerical simulations suggest that the main peak observed in 2022 was caused by meteoroids ejected from the splitting nucleus with four times the typical cometary gas expansion speed. High-resolution measurements performed with the Canadian Automated Meteor Observatory indicate that these meteoroids are fragile, with estimated bulk densities of 250 kg/m$^3$. In contrast with the main peak, the first TAH activity peak in 2022 is best modelled with trails ejected prior to 1960. We find that ordinary cometary activity could have produced other TAH apparitions observed in the past, including in 1930 and 2017. The extension of our model to future years predicts significant returns of the shower in 2033 and 2049.