Prediction of the 2001 Leonid activity and an assessment of the spacecraft impact hazard

Abstract

Different maxima in the Leonid activity observed in the same year can be identified as due to dust particles ejected during different perihelion passages of the parent comet, 55P/Tempel–Tuttle. This is because the ecliptic intersections of trajectories of particles that were ejected during different comet apparitions lie well separated in the ecliptic plane. For November 2001, we determine the ecliptic intersection points of particles originating from various apparitions of 55P/Tempel–Tuttle and thus predict the times of maximum Leonid activity. By comparing this year9s configuration with the past, we also give an estimate of the flux that might be expected in 2001. As light flashes due to Leonid impacts on the Moon can be detected on Earth, we give the times of closest approaches of dust trails to the Moon. By comparing the predicted Leonid meteoroid flux on the Earth9s atmosphere with the flux of sporadic meteoroids, we estimate that the hazard of a Leonid impact on a spacecraft in low–Earth orbit is low. However, the densest part of the Leonid trails will not reach Earth, but will cross the geo–stationary orbit (GEO) ring. The impact risk will reach its maximum for GEO satellites at longitudes between 35° and 160° W between 17.00 and 20.00 UT on 18 November 2001. While the overall risk of major damage is still relatively low, this period undoubtedly represents the greatest impact risk to spacecraft since the beginning of the space–age.