2011 UB256

 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 October 2011 by the Pan-STARRS 1 telescope system at Haleakala; the Apache Point-Sloan Digital Sky Survey had imaged this object on 31 March 2003 without identifying it as an asteroid. Its orbit is characterized by low eccentricity (0.071), moderate inclination (24.3°) 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 64 observations with a data-arc span of 6265 days. has an absolute magnitude of 19.9 which gives a characteristic diameter of 300 m.

Mars trojan and orbital evolution
Recent calculations indicate that it is a stable Mars trojan. It may not be a member of the so-called Eureka family.

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