  Here we report WFPC2 observations of the Quaoar-Weywot Kuiper belt binary.
From these observations we find that Weywot is on an elliptical orbit with
eccentricity of 0.14 {\pm} 0.04, period of 12.438 {\pm} 0.005 days, and a
semi-major axis of 1.45 {\pm} 0.08 {\times} 104 km. The orbit reveals a
surpsingly high Quaoar-Weywot system mass of 1.6{\pm}0.3{\times}10^21 kg. Using
the surface properties of the Uranian and Neptunian satellites as a proxy for
Quaoar's surface, we reanalyze the size estimate from Brown and Trujillo
(2004). We find, from a mean of available published size estimates, a diameter
for Quaoar of 890 {\pm} 70 km. We find Quaoar's density to be \rho = 4.2 {\pm}
1.3 g cm^-3, possibly the highest density in the Kuiper belt.
