Over the past decade, more than 100 binary asteroids have been discovered. There is a large variety of systems, ranging from widely spaced "double planet" pairs in the Kuiper Belt, large synchronous binaries in the main belt, small (likely collisional debris) satellites of main-belt asteroids (e.g. Dactyl about Ida), to a large number of "asynchronous binaries" among Near-Earth asteroids and small (<10 km diameter) asteroids in the inner main belt. It is this latter class of binaries, comprising about half of all those discovered, that we propose to concentrate upon. The reason for our focus on these bodies is that we can derive detailed physical parameters for these systems through radar (for NEAs) and/or lightcurves showing eclipse phenomena between the components, thus we have the necessary information (sizes and shapes of components, orbital and rotational periods, etc.) for detailed physical analysis, and we see similarities (and some differences) among the systems that allow us to infer details of the origin of these systems and their evolution into their present dynamical states. Most of these systems are "partially asynchronous", in that the primary spins with a short period, much less than the satellite orbital period, and the satellite tends to be synchronized with the orbital period. Thus, the configuration is analogous to the Earth-Moon system, where the satellite is synchronized, but not the primary. We do see a small number of systems where the satellite is not synchronized, and a few others where the system is fully synchronized, with the primary also locked to the orbit period, like the Pluto-Charon system. This range of evolutionary states provides clues to the mechanisms and time scales of evolution into the synchronous states. In all cases, we find the total angular momentum of the combined system is near the critical spin angular momentum if all of the mass were contained in a single body rather than a binary. This suggests that these systems originated by some form of fission or mass shedding of single bodies spun up to a critical spin rate. The likely cause of this spin-up is radiation torque from the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. A tabulation of these binary systems and an initial examination of angular momentum content and other physical parameters, by Pravec and Harris (Icarus 190, 250-259, 2007), was recently published with reprint available.
Thus, the goals of the proposed workshop are as follow:
To accomplish these goals, we propose to convene a 3-4 day workshop of ~20 participants, to include radar and optical (photometric) observers, and theoreticians specializing in orbital dynamics, solid body properties (mainly "rubble", or unconsolidated solid material), and computer simulations of hydrodynamic processes. Much work has been done in the past by such specialists in considering "catastrophic disruption" of asteroids by collision processes. Much of the same expertise is applicable to the somewhat more gentle processes envisaged by the slow evolution by YORP effect (although we anticipate that "landsliding" events may be as abrupt as collisions and result in similar dynamical processes).
Because our space is very limited and we desire to maintain a narrow focus on topic, attendance is by invitation only. The list of current invitees is here. If you would like to attend and you are not on the current list, please send a request to Alan Harris (with copy to Marcello Fulchignoni). Be sure to include a specific proposal of your contribution, at least a title and preferably an abstract. If you are on the current list of invitees and have not yet responded with a topic title and abstract, please do so soon. In addition to an abstract, if you have a web site or recent preprint that is relevant, please provide a URL so we can link it for other attendees to see.