Anticipation of the Ulysses Interstellar Dust findings



It has long been thought that dust particles making up the zodiacal cloud come predominantly from sources within the solar system such as short-period comets, asteroids, and Jupiter's moons. However, data received recently from the Ulysses spacecraft calls this assumption into question, indicating that most of the dust particles encountered beyond the asteroid belt are of interstellar origin [Grun et al., 1993]. The particles were found to be entering the solar system at high speed (v≥26 km/s) from the general direction of the galactic center, approximately the same ecliptic direction from which the interstellar gas wind originates.

These results do not surprise me. In my 1983 Ph.D. dissertation and in subsequent papers I had stated reasons for believing that interstellar dust has recently entered the solar system in large quantities specifically from the direction of the galactic center. I will take a moment to explain some of the reasons that led me to this conclusion because they may be helpful to the interpretation of the Ulysses findings.