  Potentially hazardous asteroid (185851) 2000 DP107 was the first binary
near-Earth asteroid to be imaged. Radar observations in 2000 provided images at
75 m resolution that revealed the shape, orbit, and spin-up formation mechanism
of the binary. The asteroid made a more favorable flyby of the Earth in 2008,
yielding images at 30 m resolution. We used these data to obtain shape models
for the two components and to improve the estimates of the mutual orbit,
component masses, and spin periods. The primary has a sidereal spin period of
2.7745 +/- 0.0007 h and is roughly spheroidal with an equivalent diameter of
863 m +/- 5 %. It has a mass of 4.656 +/- 0.43 x 10^11 kg and a density of 1381
+/- 244 kg m^{-3}. It exhibits an equatorial ridge similar to the (66391) 1999
KW4 primary, however the equatorial ridge in this case is not as regular and
has a ~300 m diameter concavity on one side. The secondary has a sidereal spin
period of 1.77 +/- 0.02 days commensurate with the orbital period. The
secondary is slightly elongated and has overall dimensions of 377 x 314 x 268 m
(6 % uncertainties). Its mass is 0.178 +/- 0.021 x 10^{11} kg and its density
is 1047 +/- 230 kg m^{-3}. The mutual orbit has a semi-major axis of 2.659 +/-
0.08 km, an eccentricity of 0.019 +/- 0.01, and a period of 1.7556 +/- 0.0015
days. The normalized total angular momentum of this system exceeds the amount
required for the expected spin-up formation mechanism. An increase of angular
momentum from non-gravitational forces after binary formation is a possible
explanation. The two components have similar radar reflectivity, suggesting a
similar composition consistent with formation by spin-up. The secondary appears
to exhibit a larger circular polarization ratio than the primary, suggesting a
rougher surface or subsurface at radar wavelength scales.
