(153591) 2001 SN263
(153591) 2001 SN263 is a small near-Earth asteroid discovered by the LINEAR project in 2001. In 2008, scientists using the planetary radar at Arecibo Observatory discovered that the object is orbited by two satellites, when the triple asteroid made a close approach to Earth of 0.066 AU (nearly 10 million kilometers). The largest body is called Alpha and is spheroid in shape, with principal axes of 2.8±.1 km, 2.7±.1 km, and 2.5±.2 km and a density of nearly 1.3±0.6 g cm−3, and the satellites, named Beta and Gamma, are several times smaller in size. Beta is 1.1 km in diameter and Gamma 0.4 km.
The only other unambiguously identified triple asteroid in the near-Earth population is (136617) 1994 CC, which was discovered to be a triple system in 2009.