Extrasolar Micrometeors Radiating from the Vicinity of the Local Interstellar Bubble

Abstract

Over 12,000 micrometeor detections obtained mainly during 1997 November 15-20 and over a similar period in 1998 with the Arecibo UHF (430 MHz) radar have been processed so far. Out of this particular sample, nearly 3000 particles show measurable decelerations from which particle sizes can be estimated and extra-atmospheric velocities obtained by direct numerical integration through an appropriate MSIS model atmosphere. From this subsample, 143 objects that either had distinct 1 AU heliocentric hyperbolic orbits or were on elliptical orbits of high eccentricity with semimajor axes greater than 5 AU were found to have originally hyperbolic orbits at distances between 50 and 100 AU. Original extrasolar orbits, velocities, and radiants have been calculated by a Cowell-method, numerical integration back 10 yr into the past, when these particles first encountered the solar system at greater than 50 AU. The perturbation calculations included solar radiation pressure, solar wind magnetic field deflections, and the gravitational influence of Jupiter, Saturn, Uranus, and Neptune. The original extrasolar particle sample was parsed down in several ways to make a final list of interstellar particle (ISP) candidates. In Galactic coordinates relative to an assumed LSR (α = 18h,δ = 30°, v = 20 km s-1), most of the remaining 108 ISP radiants form an extended cluster that appears to be coming from the region of the Local Bubble or the Local Cavity. In a new LSR determined by the mean ISP velocities, many of the particles appear to radiate from a region stretching from the Vela supernova to the vicinity of the Geminga pulsar. The Geminga supernova is a more likely source or transport agent of the Arecibo ISPs because of its greater age and relatively small distance from the Sun. The likelihood of a nearby supernova as an ISP source or at least an ISP transport mechanism is discussed is some detail. It is suggested that the Arecibo ISPs are samples at 1 AU of the particles detected earlier by the Pioneer 10 and 11 spacecraft between 5 and 18 AU.