## Five New and Three Improved Mutual Orbits of Transneptunian
Binaries.

#### W. M. Grundy, K. S. Noll, F. Nimmo, H. G. Roe, M. W. Buie,
S. B. Porter, S. D. Benecchi, D. C. Stephens, H. F. Levison,
and J. A. Stansberry.

Icarus, 213, 678-692 (2011).

### ABSTRACT

We present three improved and five new mutual orbits of transneptunian
binary systems (58534) Logos-Zoe, (66652) Borasisi-Pabu, (88611)
Teharonhiawako-Sawiskera, (123509) 2000 WK183, (149780) Altjira,
2001 QY297, 2003 QW111, and 2003 QY90 based on Hubble Space Telescope
and Keck II laser guide star adaptive optics observations. Combining
the five new orbit solutions with 17 previously known orbits yields
a sample of 22 mutual orbits for which the period P, semimajor axis
a, and eccentricity e have been determined. These orbits have mutual
periods ranging from 5 to over 800 days, semimajor axes ranging from
1600 to 37,000 km, eccentricities ranging from 0 to 0.8, and system
masses ranging from 2 × 1017 to 2 × 1022 kg. Based on the relative
brightnesses of primaries and secondaries, most of these systems consist
of near equal-sized pairs, although a few of the most massive systems are
more lopsided. The observed distribution of orbital properties suggests
that the most loosely-bound transneptunian binary systems are only found
on dynamically cold heliocentric orbits. Of the 22 known binary mutual
orbits, orientation ambiguities are now resolved for 9, of which 7 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. To the extent that other perturbations are
not dominant, the binary systems undergo Kozai oscillations of their
eccentricities and inclinations with periods of the order of tens of
thousands to millions of years, some with strikingly high amplitudes.

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