2011 SP189

 is a small asteroid and Mars trojan orbiting near the of Mars (60 degrees behind Mars on its orbit).

Discovery, orbit and physical properties
was first observed on 29 September 2011 by the Mount Lemmon Survey. Its orbit is characterized by low eccentricity (0.040), moderate inclination (19.9°) and a semi-major axis of 1.52 AU. Upon discovery, it was classified as Mars-crosser by the Minor Planet Center. Its orbit is well determined as it is currently (January 2021) based on 45 observations with a data-arc span of 2390 days. has an absolute magnitude of 20.9 which gives a characteristic diameter of 300 m.

Mars trojan and orbital evolution
Recent calculations indicate that it is a stable Mars trojan with a libration period of 1300 yr and an amplitude of 20°. These values are similar to those of 5261 Eureka and related objects and it may be a member of the so-called Eureka family.

Mars trojan
 (leading):  (trailing):
 * 5261 Eureka (1990 MB) †