2011 SP189 was first observed on 29 September 2011 by the Mount Lemmon Survey.[5] Its orbit is characterized by low eccentricity (0.040), moderate inclination (19.9°) and a semi-major axis of 1.52 AU.[5] 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.[1]2011 SP189 has an absolute magnitude of 20.9 which gives a characteristic diameter of 300 m.[1]
Mars trojan and orbital evolution
Recent calculations indicate that it is a stable L5Mars trojan with a libration period of 1300 yr and an amplitude of 20°.[2] These values are similar to those of 5261 Eureka and related objects and it may be a member of the so-called Eureka family.
Three new stable L5 Mars Trojans de la Fuente Marcos, C., de la Fuente Marcos, R. 2013, Monthly Notices of the Royal Astronomical Society: Letters, Vol. 432, Issue 1, pp. 31–35.