Search

The potentially hazardous asteroid (185851) 2000 DP107 was the first binary near-Earth asteroid to be imaged. Radar observations in 2000 provided images at 75m 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 30m 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 hr and is roughly spheroidal with an equivalent diameter of 863m ± 5%. It has a mass of 4.656 ± 0.43 × 1011 kg and a density of 1381 ± 244 kgm.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 × 314 × 268 m (6% uncertainties). Its mass is 0.178 ± 0.021 × 1011 kg and its density is 1047 ± 230 kgm.3. The mutual orbit has a semimajor 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 nongravitational 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.

The potentially hazardous asteroid (185851) 2000 DP107 was the first binary near-Earth asteroid to be imaged. Radar observations in 2000 provided images at 75m 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 30m 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 hr and is roughly spheroidal with an equivalent diameter of 863m ± 5%. It has a mass of 4.656 ± 0.43 × 1011 kg and a density of 1381 ± 244 kgm.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 × 314 × 268 m (6% uncertainties). Its mass is 0.178 ± 0.021 × 1011 kg and its density is 1047 ± 230 kgm.3. The mutual orbit has a semimajor 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 nongravitational 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.

We determine the three-dimensional shape of near-Earth Asteroid (101955) Bennu based on radar images and optical lightcurves. Bennu was observed both in 1999 at its discovery apparition, and in 2005 using the 12.6-cm radar at the Arecibo Observatory and the 3.5-cm radar at the Goldstone tracking station. Data obtained in both apparitions were used to construct a shape model of this object. Observations were also obtained at many other wavelengths to characterize this object, some of which were used to further constrain the shape modeling. The lightcurve data, along with an initial determination of the rotation period derived from them, simplified and improved the shape modeling.Below we briefly describe the observations and shape modeling process. We discuss the shape model and the implications for the possible formation and evolution of this object. We also describe the importance and limitations of the shape model in view of the fact that this object is the target of the OSIRIS-REx spacecraft mission. © 2013 Elsevier Inc.

We observed the near-Earth ASTEROID 2008 EV5 with the Arecibo and Goldstone planetary radars and the Very Long Baseline Array during December 2008. EV5 rotates retrograde and its overall shape is a 400 ± 50 m oblate spheroid. The most prominent surface feature is a ridge parallel to the asteroid's equator that is broken by a concavity about 150. m in diameter. Otherwise the asteroid's surface is notably smooth on decameter scales. EV5's radar and optical albedos are consistent with either rocky or stony-iron composition. The equatorial ridge is similar to structure seen on the rubble-pile near-Earth asteroid (66391) 1999 KW4 and is consistent with YORP spin-up reconfiguring the asteroid in the past. We interpret the concavity as an impact crater. Shaking during the impact and later regolith redistribution may have erased smaller features, explaining the general lack of decameter-scale surface structure. © 2011 Elsevier Inc.