21900 Orus /ˈɔːrəs/ is a Jupiter trojan asteroid from the Greek camp, approximately 53 kilometers (33 miles) in diameter, and a target of the Lucy mission to be visited in November 2028.

[7] It was discovered on 9 November 1999, by Japanese amateur astronomer Takao Kobayashi at his private Ōizumi Observatory in Gunma Prefecture, Japan, and later named Orus after a slain Achaean warrior from the Iliad.

The flyby is scheduled for 11 November 2028, and will approach the asteroid to a distance of 1,000 km (620 mi) at a relative velocity of 7.1 km/s (16,000 mph).

[9] Orus is characterized as a D-type and C-type asteroid by the Lucy mission team and by Pan-STARRS photometric survey, respectively.

[7][10] In 2016, Mottola published a revised rotation period of 13.48617±0.00007 h, from ground-based observations taken over five apparitions in support of the Lucy mission.