Tidal dissipation of binaries in asteroid pairs

Abstract

Tidal dissipation in a celestial body can be used to probe its internal structure. Tides govern the orbital evolution of binary systems and therefore constraints on the interior of binary system members can be derived by knowing the age and tidal state of the binary system. For asteroids, age estimates are challenging due to a lack of direct observation of their surface. However, the age of asteroid pairs formed by rotational fission of a parent body can be derived from dynamical modeling, and as such can be used to constrain the age of binary systems existing within asteroid pairs. We study 13 binary asteroid systems existing in asteroid pairs by modeling their tidal locking and eccentricity damping timescales from tidal dissipation in the primaries and secondaries. We consider the impact of thermal torques on these timescales from the YORP and BYORP effects. The resulting constraints on the tidal dissipation ratio Q/k2 are compared to monolithic and rubble pile asteroid theories, showing that all secondaries are consistent with rubble piles with regolith layers greater than 3 m and suggest that Q/k2 for rubble piles increases with radius. A particular case is the first bound secondary of asteroid (3749) Balam, whose Q/k2 is constrained to be between 2.7 ×104 and 1.4 ×106, consistent with a rubble-pile with a regolith thickness between 30 m and 100 m.