A Technique for measuring the interstellar component of cosmic dust

Abstract

That there is an interstellar (IS) component in cosmic dust has been demonstrated by Pioneers 8 and 9 (Wolf, Rhee, and Berg, 1975). The Pioneer spacecrafts distinguished the IS from interplanetary (IP) dust by measuring particle velocity and direction. Unfortunately, detectors that are capable of measuring a particle’s velocity and direction are so restricted in their sensitive area and/or solid angle that their event rate is very low. Pioneers 8 and 9, for example, detected 1-5 IS particles out of 20 events in 7 spacecraft-years of operation (Wolf, Rhee, and Berg, 1976). More events can be obtained, however, if one uses a detector that only measures the direction of travel. The direction alone can be sufficient to distinguish between IS and IP dust—at least on a statistical basis. For example, if most IP dust travels in directions near the ecliptic plane, then an IS flux from out of the plane should be detectable. This paper will examine the use of direction alone in detecting IS particles.