During the 2011 opposition, the last opposition of 2009 BD that was observed, 2009 BD approached on June 2, 2011 within 0.00231 AU (346,000 km) of the Earth, which is less than 1 lunar distance. For comparison, the distance to the Moon is about 0.0026 AU (384,400 km).
JPL[2] and MPC[1] give different parameters for the orbit of 2009 BD, affecting whether the orbit type should be considered an Apollo asteroid or an Amor asteroid. JPL includes non-gravitational acceleration parameters in the orbital solution.
Physical characteristics
Because 2009 BD is a very small multi-opposition near-Earth object, the effect of radiation pressure on the orbit caused by light from the Sun was able to be detected.[4] The radiation-related acceleration allowed the Area to Mass Ratio (AMR) to be estimated at (2.97 ± 0.33) × 10−4 m2/kg. Assuming an albedo of 0.12, a typical average for asteroids in the inner solar system, this AMR corresponds to a density of about 640 kg/m3. This density is consistent with the density of very porous rock. For comparison, the asteroid 2006 RH120 has a measured density of about 400 kg/m3, and the density of the asteroid 253 Mathilde as measured by the NEAR-Shoemaker space probe was 1300 kg/m3. In contrast, the density of the man-made near-Earth object 6Q0B44E is 15 kg/m3.
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