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Title: Orbital clustering of Martian Trojans: An asteroid family in the inner solar system?
Authors: Apostolos A. Christou

We report on the discovery of new Martian Trojans within the Minor Planet Centre list of asteroids. Their orbital evolution over 10^8 yr shows characteristic signatures of dynamical longevity (Scholl et al, 2005) while their average orbits resemble that of the largest known Martian Trojan, 5261 Eureka. The group forms a cluster within the region where the most stable Trojans should reside. Based on a combinatorial analysis and a comparison with the Jovian Trojan population, we argue that both this feature and the apparent paucity of km-sized Martian Trojans (Trilling et al, 2006) as compared to expectations from earlier work (Tabachnik and Evans, 1999) is not due to observational bias but instead a natural end result of the collisional comminution (Jutzi et al, 2010) or, alternatively, the rotational fission (Pravec et al, 2010) of a progenitor L5 Trojan of Mars. Under the collisional scenario in particular, the new Martian Trojans are dynamically young, in agreement with our age estimate of this "cluster" of < 2 Gyr based on the earlier work of Scholl et al. This work highlights the Trojan regions of the Terrestrial planets as natural laboratories to study processes important for small body evolution in the solar system and provides the first direct evidence for an orbital cluster of asteroids close to the Earth.

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Title: Three new stable L5 Mars Trojans
Authors: C. de la Fuente Marcos, R. de la Fuente Marcos

Mars was second to Jupiter in being recognised as the host of a population of Trojan minor bodies. Since 1990, 5 asteroids -5261 Eureka, (101429) 1998 VF31, (121514) 1999 UJ7, 2001 DH47 and (311999) 2007 NS2- have been identified as Mars Trojans, 1 L4 and 4 L5. Dynamical and spectroscopic evidence suggests that some Mars Trojans may be remnants of the original planetesimal population that formed in the terrestrial planets region. Here we revisit the long-term dynamical evolution of the previously known Mars Trojans and show that 2011 SC191, 2011 SL25 and 2011 UN63 are also trailing (L5) Mars Trojans. They appear to be as stable as Eureka and may have been Trojans over the age of the Solar system. The fact that 5 Trojans move in similar orbits and one of them is a binary may point to the disruption of a larger body early in the history of the Solar system. Such a catastrophic event may also explain the apparently strong asymmetry in terms of number of objects (1 vs. 7) between the L4 and L5 regions. Future spectroscopic observations should be able to reject or confirm a putative common chemical signature that may lend further support to a collisional scenario.

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