Mars trojan

The Mars trojans are a group of Trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars. The origin of the Mars trojans is not well understood. One theory suggests that they were primordial objects left over from the formation of Mars that were captured in its Lagrangian points as the Solar System was forming. However, spectral studies of the Mars trojans indicate this may not be the case.[1][2] Another explanation involves asteroids chaotically wandering into the Mars Lagrangian points later in the Solar System's formation. This is also questionable considering the short dynamical lifetimes of these objects.[3][4] The spectra of Eureka and two other Mars trojans indicates an olivine-rich composition.[5] Since olivine-rich objects are rare in the asteroid belt it has been suggested that some of the Mars trojans are captured debris from a large orbit-altering impact on Mars when it encountered a planetary embryo.[6][3]

The L5 group (shown in green) and the L4 group (light blue) of Mars and Jupiter Trojan asteroids shown along with the orbits of Jupiter and the inner planets. Mars is shown in red. The outer orbit is that of Jupiter.
Animation of 1999 UJ7 relative to Sun and Mars 1600-2500
   Sun ·   1999 UJ7 ·   Mars
Animation of 2007 NS2 relative to Sun and Mars 1600-2500
   Sun ·   2007 NS2 ·   Mars

Presently, this group contains seven asteroids confirmed to be stable Mars trojans by long-term numerical simulations but only four of them are accepted by the Minor Planet Center (†)[7] and there is one candidate.[3][4][8][9]

Due to close orbital similarities, most of the smaller members of the L5 group are hypothesized to be fragments of Eureka that were detached after it was spun up by the YORP effect (Eureka's rotational period is 2.69 h). The L4 trojan 1999 UJ7 has a much longer rotational period of ~50 h, apparently due to a chaotic rotation that prevents YORP spinup.[10]

L4 (leading):

L5 (trailing):

Candidates

See also

References
  1. Rivkin, Andrew; Trilling, David; Thomas, Cristina; DeMeo, Fancesca; Spahr, Timoth; Binzel, Richard (2007). "Composition of the L5 Mars Trojans: Neighbors, not siblings". Icarus. 192 (2): 434–441. arXiv:0709.1925. Bibcode:2007Icar..192..434R. doi:10.1016/j.icarus.2007.06.026.
  2. Trilling, David; Rivking, Andrew; Stansberry, John; Spahr, Timothy; Crudo, Richard; Davies, John (2007). "Albedos and diameters of three Mars Trojan asteroids". Icarus. 192 (2): 442–447. arXiv:0709.1921. Bibcode:2007Icar..192..442T. doi:10.1016/j.icarus.2007.08.002.
  3. Scholl, H.; Marzari, F.; Tricarico, P. (2005). "Dynamics of Mars Trojans". Icarus. 175 (2): 397–408. Bibcode:2005Icar..175..397S. doi:10.1016/j.icarus.2005.01.018.
  4. Schwarz, R.; Dvorak, R. (2012). "Trojan capture by terrestrial planets". Celestial Mechanics and Dynamical Astronomy. 113 (1): 23–34. arXiv:1611.07413. Bibcode:2012CeMDA.113...23S. doi:10.1007/s10569-012-9404-4.
  5. Borisov, G.; Christou, A.; Bagnulo, S.; Cellino, A.; Kwiatkowski, T.; Dell'Oro, A. (2017). "he olivine-dominated composition of the Eureka family of Mars Trojan asteroids". Monthly Notices of the Royal Astronomical Society. 466 (1): 489–495. arXiv:1701.07725. Bibcode:2017MNRAS.466..489B. doi:10.1093/mnras/stw3075.
  6. Polishook, D.; Jacobson, S. A.; Morbidelli, A.; Aharonson, O. (2017). "A Martian origin for the Mars Trojan asteroids". Nature Astronomy. 1: 0179. arXiv:1710.00024. Bibcode:2017NatAs...1E.179P. doi:10.1038/s41550-017-0179.
  7. "List Of Martian Trojans". Minor Planet Center. Retrieved 2013-03-04.
  8. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (April 2013). "Three new stable L5 Mars Trojans". Monthly Notices of the Royal Astronomical Society: Letters. 432 (1): L31–L35. arXiv:1303.0124. Bibcode:2013MNRAS.432L..31D. doi:10.1093/mnrasl/slt028.
  9. Christou, A. A. (2013). "Orbital clustering of Martian Trojans: An asteroid family in the inner solar system?". Icarus. 224 (1): 144–153. arXiv:1303.0420. Bibcode:2013Icar..224..144C. doi:10.1016/j.icarus.2013.02.013.
  10. Lovett, R. (2017-10-20). "Sun's light touch explains asteroids flying in formation behind Mars". Science. doi:10.1126/science.aar2794.
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