  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 2 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 1,600 to 37,000 km, eccentricities ranging from 0 to 0.8, and
system masses ranging from 2 x 10^17 to 2 x 10^22 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 or-bits, orientation
ambiguities are now resolved for 9, of which 7 are prograde and 2 are
retro-grade, 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.

Earth and Planetary Astrophysics