From the LANL preprint server at
http://xxx.lanl.gov/abs/astro-ph/0407362

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Astrophysics, abstract
astro-ph/0407362
From: Keith Noll [view email]
Date: Fri, 16 Jul 2004 18:27:39 GMT (110kb)

The Orbit and Albedo of Transneptunian Binary 1997 CQ29
Authors: Keith S. Noll, Denise C. Stephens, Will M. Grundy, David J.
Osip, Ian Griffin
Comments: accepted for publication in the Astronomical Journal,
November 2004 18 pages, 5 figuers

We have measured the separations and position angles of the two
components of the binary transneptunian object 1997 CQ29 at eight
epochs. From these data we are able to constrain the orbit and mass
of this binary system. The best fitting orbit has an orbital period
of P = 312+/-3 days. The orbital eccentricity is e = 0.45+/-0.03 and
the semimajor axis is a = 8,010+/-80 km. The mass of the system is
surprisingly low at 0.42+/-0.02 x 10^18 kg. To account for the
observed brightness consistent with the low mass and a range of
plausible densities, the geometric albedo must be very high; for an
assumed density of 1000 kg m^-3 we find a red geometric albedo of
p_R = 0.37, an order of magnitude higher than has been generally
assumed for transneptunian objects. If objects with comparably high
albedos are common in the Kuiper belt, estimates of the mass of the
belt must be significantly reduced. The semimajor axis of 1997
CQ29's orbit is 2.8% of the Hill radius of the primary, a value
strikingly similar to this same ratio in other transneptunian
binaries, main-belt binaries, and regular satellite systems.