Radar Imaging and Characterization of Binary Near-Earth Asteroid (185851) 2000 DP107

TL;DR

This study used radar imaging from 2000 and 2008 to model the shape, orbit, and physical properties of the binary near-Earth asteroid (185851) 2000 DP107, revealing details about its formation, composition, and dynamics.

Contribution

The paper provides detailed shape models, mass, density, and orbital parameters of the binary asteroid based on radar data, improving understanding of its formation and physical characteristics.

Findings

Primary has a spin period of 2.7745 hours and a diameter of 863 m.

Secondary has a spin period of 1.77 days and dimensions of 377 x 314 x 268 m.

Mutual orbit semi-major axis is 2.659 km with low eccentricity.

Abstract

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.