Techniques for galactic dust measurements in the heliosphere

Abstract

Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently, the Ulysses dust detector has identified and measured interstellar dust outside 1.8 AU from the Sun at ecliptic latitudes above 50°. Inside this distance it could not reliably distinguish interstellar from interplanetary dust. Modeling the Ulysses data suggests that up to 30% of dust flux with masses above 10−16 kg at 1 AU is of interstellar origin. From the Hiten satellite in high eccentric orbit about the Earth, there are indications that ISD indeed reaches the Earth's orbit. Two new missions carrying dust detectors, Cassini and Stardust, will greatly increase our observational knowledge. In this paper we briefly review instruments used on these missions and compare their capabilities. The Stardust mission [Brownlee et al., 1996] will analyze the local interstellar dust population by an in situ chemical analyzer and collect ISD between 2 and 3 AU from the Sun. The dust analyzer on the Cassini mission will determine the interstellar dust flux outside Venus' orbit and will provide also some compositional information. Techniques to identify the ISD flux levels at 1 AU are described that can quantify the interstellar dust flux in high Earth orbit (outside the debris belts) and provide chemical composition information of galactic dust.