Transneptunian Binaries: Statistics of Orbital Properties
William M. Grundy
, K. S. Noll
, M. W. Buie
, S. D. Benecchi
, H. G. Roe
, S. B. Porter
, F. Nimmo
, J. A. Stansberry
, D. C. Stephens
, H. F. Levison
We present new mutual orbits of transneptunian binary systems (TNBs) from Hubble Space Telescope and Keck 2 laser guide star adaptive optics observations. Combining our new orbit solutions with previously published orbits yields a growing sample of mutual orbits for which the period P, semimajor axis a, and eccentricity e are known (23 and counting).
The observed distribution of orbital properties reveals several interesting characteristics. The most loosely-bound TNB systems only occupy dynamically cold heliocentric orbits, implying a link between the mechanism that excited the heliocentric orbits and the stripping of loose binaries (although it remains possible that differences already existed before the excitation of the heliocentric orbits). The existence of a number of TNBs with near-circular mutual orbits suggests that small transneptunian bodies could be highly dissipative, in order for them to have become tidally circularized within 4.5 Gyr. Many TNB systems undergo Kozai oscillations of their eccentricities and inclinations. The amplitudes of these oscillations can be quite large for some of the more highly inclined systems. However, we see no evidence for any paucity of highly inclined systems, as might be expected if the highest amplitude eccentricity oscillations resulted in stripping of satellites or particularly rapid tidal dissipation and coalescence.
Of our binary mutual orbits, sky-plane orientation ambiguities are now resolved for 8, of which 6 are prograde and 2 are retrograde, consistent with a random distribution of orbital orientations, but not with models predicting a strong preference for retrograde orbits, as would be expected if dynamical friction from a sea of small bodies gradually tightened transiently captured binaries. Likewise, the existence of 2 retrograde orbits seems inconsistent with the uniformly prograde orbits expected if TNBs accreted via the streaming instability mechanism.
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42nd DPS Program published in BAAS volume 42 #4, 2010.
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