Identification of meteoroid streams from Apollo asteroids in the Adelaide radar orbit surveys

Abstract

A search is made for asteroid-related meteoroids among the 3759 orbits determined in the two Adelaide radar meteor orbit surveys of the 1960s; these are the only southern hemisphere surveys yet completed. All meteor orbits are compared to the orbits of all known comets and established meteor showers. For the comets comparatively modest numbers of correlated meteors are found. In contrast, a similar comparison with the orbits of all Aten, Apollo and Amor asteroids discovered through 1986 October reveals strong meteor associations for several of the Apollo asteroids. A new and powerful technique is developed which allows the recognition of streams associated with specific parent objects, when large orbit surveys are analyzed. Apart from 3200 Phaethon, the Geminid parent, meteoroid streams are found to be associated with 1566 Icarus, 2101 Adonis, 2201 Oljato, 2212 Hephaistos, 1937 UB (Hermes), 5025 P-L, 1982 TA, and 1984 KB. These all give rise to meteors of velocity at least ∼22 km sec −1. There is also evidence of meteor activity for a few other Apollos; no streams are found for any of the Atens or Amors. Theoretical radiants and velocities are calculated for all asteroids of perihelion distance less than 1.025 AU which approach the Earth to within 0.1 AU, and it is shown that the lack of observed meteor streams for each can be explained in terms of the radiants being inaccessible from the Adelaide site (35°S), the lack of observations at the appropriate time of year, or the expected meteor velocities being below 20 km sec −1 and hence producing little ionization and having a severely reduced probability of detection. It therefore appears that meteoroid streams are a general feature associated with Apollo asteroids.