On the bulk density of the M-type asteroid 16 Psyche

Abstract

Recent estimates of the bulk density of the largest M-type asteroid 16 Psyche (1.4 and 1.8 g/cm3) seem to be too low for asteroids of this type. The interpretation of such low densities for the asteroid 16 Psyche with its increased metal content led to estimates of its macroporosity of 70%. In the present paper, it has been shown that the extremely low density estimates are caused primarily by the usage of a very high value of the IRAS diameter of the asteroid (D = 264 km, which corresponds to an IRAS albedo of 0.10). The application of the more accurate polarimetric albedo (0.170) and diameter (213 km) of Psyche results in a bulk density of the asteroid of 3.3 ± 0.7 g/cm3. For a moderate asteroid macroporosity of 30-40%, this density even agrees with the 50% metal content and, therefore, removes both the contradiction with the radar data and the problems of the very low density and unlikely high porosity of the asteroid 16 Psyche. © Pleiades Publishing, Inc., 2006.