HR: 0800h
AN: P11B-0120    [Abstracts]
TI: Satellite Capture via Binary Exchange Reactions: Application to Triton
AU: * Agnor, C
EM: cagnor@pmc.ucsc.edu
AF: University of California Santa Cruz, Earth Science Department 1156 High Street, Santa Cruz, CA 95064 United States
AU: Hamilton, D P
EM: hamilton@astro.umd.edu
AF: University of Maryland, Department of Astronomy, College Park, MD 20742-242 United States
AB: The recent observational discovery of satellites orbiting asteroids and Kuiper belt objects has revealed a whole new constituency of solar system objects. Binaries appear to be ubiquitous among the minor planets, representing about 16% of near-Earth asteroids (Margot et al.~2002), at least 2% of asteroids in the main belt (Merline et al.~2002), and a growing number of Kuiper belt objects (currently estimated at about 14%, Noll 2005). Given the existence and prevalence of binaries, 3-body encounters between a binary pair and a third body become an inevitable and frequent occurrence in the dynamical evolution of the solar system. While 3-body encounters have been studied extensively in the context of stellar clusters, their significance in the context of solar system dynamics is only beginning to be examined and appreciated (Funato et al.~2004). We are examining how exchange reactions during planet-binary encounters (i.e.~an encounter in which one member of a binary is expelled and its place taken by the planet) represent a new pathway for the capture of planetary satellites. This new capture mechanism may be relevant to origin and evolution of several small body populations in the solar system (e.g.~the icy and irregular satellites of the giant planets). Using numerical integrations of 3-body encounters and analytic arguments we have developed a simple model to describe this purely gravitational mode of satellite capture. Capture via exchange reaction requires gravitational disruption of the binary and retention of one member by the planet. In general, we have found that exchange capture is efficient when binaries approach the planet to a distance less than the appropriate Roche radius of the system and with sufficiently low encounter velocities. As a first application of this capture mechanism, we have explored the possibility that Neptune's massive retrograde satellite Triton was captured during a gravitational encounter between Neptune and a binary composed of Triton and a third body. We have found that Triton's capture can be realized from a variety of binaries, including ones in which Triton is the more massive member and those resembling the Pluto-Charon pair (i.e.~mass ratio m_Pluto/m_Charon = 8 and semi-major axis to primary radius ratio a_B/R_Pluto = 17.3). We will discuss the encounter dynamics required for capture via this mechanism, relate them to the dynamical environment of Neptune's accretion and putative migration and discuss the conditions in which this mode of satellite capture is favored over others suggested for Triton (e.g.~collisional capture, Goldreich et al.~1989, gas drag capture, McKinnon and Leith 1994).
DE: 5455 Origin and evolution
DE: 6035 Orbital and rotational dynamics
DE: 6261 Triton
SC: Planetary Sciences [P]
MN: Fall Meeting 2005