Implications Regarding the Energetics Of the Collisional Formation of Kuiper Belt Satellites

Abstract

Recently, it has been discovered that at least 1% of Kuiper Belt Objects (KBOs) are accompanied by large satellites. Here we examine the energetics of KBO satellite formation via collisions, finding collisions require a dynamically excited Kuiper Belt. Further, even under optimistic assumptions (including perfect accretion of the satellites), we find that collisional processes cannot make KBO satellites at the observed frequency of occurrence unless KBO projectiles large enough to generate the observed satellites were \~40 times more numerous in the ancient past, resulting in an increased collision rate with sufficiently large projectiles, or unless the fraction of impact energy estimated to be imparted to ejecta is of order unity. Neither alternative is very palatable. However, an easier to accept alternative also exists: KBO primary and/or KBO satellite surface albedos presently be underestimated by making the canonical assumption of 4% surface albedos; specifically, surface albedos of KBO primaries and/or their satellites could be in the neighborhood of 15% (or higher). This would reduce KBO primary and/or satellite sizes and masses, thereby in turn reducing the required size of the impacting projectiles required to generate KBO satellites, which in turn would increase the impact rate with sufficiently large projectiles to values in line with the observed fraction of KBOs with large satellites. This proposition is expected to be easily testable with by SIRTF and by other means in the next 2 to 3 years.