2011 SC₁₉₁ is a small asteroid and Mars trojan orbiting near the L₅ point of Mars (60 degrees behind Mars on its orbit).^[2][3]

2011 SC₁₉₁ was first observed on 21 March 2003 by the Near-Earth Asteroid Tracking (NEAT) project at Palomar Observatory using the Samuel Oschin telescope and given the provisional designation 2003 GX₂₀. The object was subsequently lost and re-discovered on 31 October 2011 by the Mt. Lemmon Survey.^[4][5] Its orbit is characterized by low eccentricity (0.044), moderate inclination (18.7°) 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 (March 2013) based on 45 observations with a data-arc span of 3,146 days.^[1] 2011 SC₁₉₁ has an absolute magnitude of 19.3 which gives a characteristic diameter of 600 m.^[1]

Recent calculations indicate that it is a stable L₅ Mars trojan with a libration period of 1300 yr and an amplitude of 18°.^[2][3] These values as well as its short-term orbital evolution are similar to those of 5261 Eureka. Its eccentricity oscillates mainly due to secular resonances with the Earth and the oscillation in inclination is likely driven by secular resonances with Jupiter.^[2]

Long-term numerical integrations show that its orbit is very stable on Gyr time-scales (1 Gyr = 1 billion years). As in the case of Eureka, calculations in both directions of time (4.5 Gyr into the past and 4.5 Gyr into the future) indicate that 2011 SC₁₉₁ may be a primordial object, perhaps a survivor of the planetesimal population that formed in the terrestrial planets region early in the history of the Solar System.^[2]

• 5261 Eureka (1990 MB)
• (101429) 1998 VF31
• (121514) 1999 UJ7
• (311999) 2007 NS2
• (385250) 2001 DH47
• 2009 SE
• 2011 SL25
• 2011 SP189
• 2011 UB256
• 2011 UN63
• 2016 CP31
• 2018 EC4
• 2018 FC4
• 2020 VT1

Further reading

• 2011 SC191 Pettarin, E., Vivona, M., McMillan, R. S., Pietschnig, M., Klein, M., Boattini, A., Gibbs, A. R., Ahern, J. D., Beshore, E. C., Garradd, G. J., Grauer, A. D., Hill, R. E., Kowalski, R. A., Larson, S. M., McNaught, R. H., Birtwhistle, P. 2011, Minor Planet Electronic Circular, 2011-T02.
• 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.
• Orbital clustering of Martian Trojans: An asteroid family in the inner solar system? Christou, A. A. 2013, Icarus, Vol. 224, Issue 1, pp. 144–153.

• 2011 SC₁₉₁ data at MPC.
• 2011 SC191 at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 2011 SC191 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters