The Asteroid Belt: Doubts about the Particle Concentration Measured with the Asteroid/Meteoroid Detector on Pioneer 10

Comment on the composition of soberman particulates in the asteroid belt

“…In order to explain the disc.rePahcy between the i. nterplanetary light brightness as measured and as calculated from the Pioneer 10 results, Soberman et al [1974b] hypothesized thht the interplanetar•y particulates are no• diffusely reflecting spheres butt rather are irregularly shaped r specularly reflecting, and rapidly rotating particulates having a very low average geometric albedo of the order ofp•v = 0.01 and a strong specular component corresponding to a momentary maximum albedo oe• = 0.2. We have shown [AUer, 1974] that the concentration of particulates in the asteroid belt reported by Soberman et al [1974a ] is at least a factor of 48 too high .to be consistent with earlier gegenschein observations, provided one assumes a constant particle albedo oe = 0.2. While the factor of 48 was based on a gegenschein brightness of 260 Sx0 units [Weinberg, 1964], a careful survey from Pioneer 10 recently gave 200 Sx0 units [Hanner et al, 1974i, andZook andSoberman [1974] preliminarily reported an even lower value of 90 S•0 units.…”

The Dawn of Dust Astronomy

“…Because of too low preset threshold sensitivity, however, the instrument was very noisy and no single trajectory could be uniquely identified (Auer, 1974). Due to this inability to determine meteoroid trajectories of the Pioneer AMD instrument, the proposed twin AMD instrument was removed from the preliminary Voyager payload.…”

“…The first dust analyzers used in space were compositional analyzers. Early laboratory studies of impact ionization already used a TOF impact mass spectrometer to analyze the ions released during a hypervelocity impact (Auer andSitte, 1968, Hansen, 1968). The mass resolutions of the spectra obtained in the laboratory were low (M/DM ~ 30), mostly because of electronic limitations.…”