(21601) 1998 XO89, provisional designation 1998 XO89, is a Jupiter trojan from the Greek camp, approximately 55 kilometers (34 miles) in diameter. It was discovered on 15 December 1998, by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Lab's ETS near Socorro, New Mexico. The dark Jovian asteroid has a rotation period of 12.7 hours and belongs to the . It has not been named since its numbering in February 2001.