2006AJ....132.1624J

Planet-crossing object 2005 UD is dynamically similar to purported Geminid meteor-stream parent 3200 Phaethon, suggesting an association between the two. We present new physical observations taken to characterize 2005 UD when at 1.6 AU from the Sun. Assuming equal albedos, 2005 UD is about 4 times smaller than 3200 Phaethon, with a diameter of ∼1.3±0.1 km. The body shows periodic brightness variations of 0.4 mag that are compatible with an aspherical nucleus in rotation with a period near 5.2 hr. At optical wavelengths, 2005 UD is similar to or slightly bluer than the Sun. This property is relatively uncommon among near-Earth objects but is shared by Phaethon, strengthening the association between the two. No evidence for ongoing mass loss at rates as small as 0.01 kg/s is found in the surface brightness profile, and we conclude that the fraction of the surface that is losing mass is not greater than 10^–4. Overall, we conclude that the dynamical similarities between 2005 UD and 3200 Phaethon are matched by physical similarities between these bodies, except that the former contains only about 2% of the mass of the latter. Phaethon, 2005 UD, and the Geminid meteoroids may be fragments produced by the breakup of a precursor object.