(450894) 2008 BT18
In 2008, its minor-planet moon, designated , was discovered by radar astronomers. It measures approximately 200 meters in diameter, or one third of its primary. Orbit and classification. orbits the Sun at a distance of 0.9–3.5 AU once every 3 years and 4 months (1,209 days). Its orbit has an eccentricity of 0.59 and an inclination of 8° with respect to the ecliptic. Published by the Digitized Sky Survey, a first precovery was taken at Palomar Observatory in 1955, extending the asteroid's observation arc by 53 years prior to its discovery. The asteroid has a  low Earth minimum orbit intersection distance of which corresponds to 4.2 lunar distances (LD). On 14 July 2008, it transited Earth within 0.015 AU (5.9 LD). Physical characteristics. has been characterized as a V-type asteroid by astronomers using the SpeX spectrograph at NASA Infrared Telescope Facility, IRTF. Rotation period. A rotational lightcurve for was obtained from photometric observations made by astronomer Alberto Silva Betzler at Salvador, Brazil, in July 2008. The lightcurve gave a rotation period of hours with a brightness variation of 0.04 in magnitude (). Binary system. On 6 and 7 July 2008, research conducted using the Arecibo  Observatory produced evidence that is a synchronous binary asteroid with a minor-planet moon in its orbit. The secondary component, provisionally designated , has a diameter of at least 200 meters, about 33% the size of and up to 1.5 kilometers apart from its primary. The "Collaborative Asteroid Lightcurve Link" assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 650 meters, based on an absolute magnitude of 18.3. There are more than 60 binary near-Earth objects known to exist (2016). Mineralogy. On 26 July 2008, observations at the IRTF using the SpeX-spectrograph showed that  is a basaltic achondrite, suggesting that its parent body was subjected to sufficiently high temperatures to produce a eutectic melt. The body's surface is thought to be dominated by iron-rich orthopyroxenes with little or no olivine. Naming. As of 2017, this minor planet remains unnamed.