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RE: Mars Trojan
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Mars Trojans may be part of a planet that was destroyed long ago

In 2013, Apostolos Christou at the Armagh Observatory and Planetarium in the UK, was studying a Mars Trojan nicknamed Eureka when he spotted a group of asteroids accompanying it. They all seemed to occupy the same area in Mars's orbital path, which was strong circumstantial evidence that they shared a common ancestor.
Previous research on Eureka showed it is rich in a mineral called olivine, which typically forms within the mantles of large rocky bodies, such as Earth and the other terrestrial planets. This implies the asteroid was once part of a bigger object, maybe even a planet, that has long since been destroyed. But asteroids like this are quite rare.
To find out if Eureka's fellow Trojans also contained olivine, Christou studied the spectrum of sunlight that two of them reflected and found they did. This suggests that mantle material existed near Mars when it was forming.

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Title: The olivine-dominated composition of the Eureka family of Mars Trojan asteroids
Author: G. Borisov, A. Christou, S. Bagnulo, A. Cellino, T. Kwiatkowski, A. Dell'Oro

We have used the XSHOOTER echelle spectrograph on the European Southern Obseratory (ESO) Very Large Telescope (VLT) to obtain UVB-VIS-NIR (ultraviolet-blue (UVB), visible (VIS) and near-infrared (NIR)) reflectance spectra of two members of the Eureka family of L5 Mars Trojans, in order to test a genetic relationship to Eureka. In addition to obtaining spectra, we also carried out VRI photometry of one of the VLT targets using the 2-m telescope at the Bulgarian National Astronomical Observatory - Rozhen and the two-channel focal reducer. We found that these asteroids belong to the olivine-dominated A, or Sa, taxonomic class. As Eureka itself is also an olivine-dominated asteroid, it is likely that all family asteroids share a common origin and composition. We discuss the significance of these results in terms of the origin of the martian Trojan population.

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Asteroid (5261) Eureka was discovered by David H. Levy and Henry Holt at Palomar Observatory on June 20, 1990, and turned out to be the first known trojan asteroid of Mars.[1] It trails Mars (at the L5 point) at a distance varying by only 0.3 AU during each revolution (with a secular trend superimposed, changing the distance from 1.5-1.8 AU around 1850 to 1.3-1.6 AU around 2400). Minimum distances from the Earth, Venus, and Jupiter, are 0.5, 0.8, and 3.5 AU, respectively.

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Title: An optimal Mars Trojan asteroid search strategy
Authors: M. Todd, P. Tanga, D.M. Coward, M.G. Zadnik

Trojan asteroids are minor planets that share the orbit of a planet about the Sun and librate around the L4 or L5 Lagrangian points of stability. Although only three Mars Trojans have been discovered, models suggest that at least ten times this number should exist with diameters >= 1 km. We derive a model that constrains optimal sky search areas and present a strategy for the most efficient use of telescope survey time that maximises the probability of detecting Mars Trojans. We show that the Gaia space mission could detect any Mars Trojans larger than 1 km in diameter, provided the relative motion perpendicular to Gaia's CCD array is less than 0.40 arcsec per second.

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Asteroid (5261) Eureka
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Asteroid (5261) Eureka was discovered by Palomar Observatory on June 20, 1990, and turned out to be the first known Lagrangian asteroid of Mars.

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Title: Albedos and diameters of three Mars Trojan asteroids
Authors: D. E. Trilling (1), A. S. Rivkin (2), J. A. Stansberry (1), T. B. Spahr (3), R. A. Crudo (1,4), J. K. Davies (5) ((1) Arizona, (2) JHU/APL, (3) Harvard/Smithsonian, (4) Connecticut, (5) UK Astronomy Technology Centre)

We observed the Mars Trojan asteroids (5261) Eureka and (101429) 1998 VF31 and the candidate Mars Trojan 2001 FR127 at 11.2 and 18.1 microns using Michelle on the Gemini North telescope. We derive diameters of 1.28, 0.78, and <0.52 km, respectively, with corresponding geometric visible albedos of 0.39, 0.32, and >0.14. The albedos for Eureka and 1998 VF31 are consistent with the taxonomic classes and compositions (S(I)/angritic and S(VII)/achrondritic, respectively) and implied histories presented in a companion paper by Rivkin et al. Eureka's surface likely has a relatively high thermal inertia, implying a thin regolith that is consistent with predictions and the small size that we derive.

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Title: Composition of the L5 Mars Trojans: Neighbours, not Siblings
Authors: Andrew S. Rivkin, David E. Trilling, Cristina A. Thomas, Francesca DeMeo, Timothy B. Spahr, Richard P. Binzel

Mars is the only terrestrial planet known to have Trojan (co-orbiting) asteroids, with a confirmed population of at least 4 objects. The origin of these objects is not known; while several have orbits that are stable on solar-system timescales, work by Rivkin et al. (2003) showed they have compositions that suggest separate origins from one another. We have obtained infrared (0.8-2.5 micron) spectroscopy of the two largest L5 Mars Trojans, and confirm and extend the results of Rivkin et al. (2003). We suggest that the differentiated angrite meteorites are good spectral analogues for 5261 Eureka, the largest Mars Trojan. Meteorite analogues for 101429 1998 VF31 are more varied and include primitive achondrites and mesosiderites.

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Title: Dynamical Lifetimes of Mars Trojans
Authors: Scholl, H.; Marzari, F.; Tricarico, P.

Several authors investigated within the last ten years the stability of known Mars Trojans. A maximum of five Trojans were quoted to librate around L5 and one around L4. Recent orbital data yield less Mars Trojans. According to our computations using orbital elements of Bowell's catalogue (march 2004), only three of the known asteroids, (5261) Eureka, 1998 VF31 and 2001 DH47 appear to librate around L5 over at least 1 Myr. Other previously quoted Mars Trojans are no more in the Trojan region, presumably due to an orbital improvement. We investigated the dynamical lifetime of the longest observed Trojan, Eureka, by two methods: i) by applying Laskar's frequency analysis and ii) by integrating the orbit of Eureka surrounded by a cloud of clones over several Gyrs. The Yarkovski effect is also taken into account in some integrations. The dynamical lifetime of Eureka is found to be of the order of 2-3 Gyrs. Spectroscopic and photometric results by Rivkin et al. (2003) suggest that Eureka is a highly differentiated kilometre-sized body. Its parent body was a much larger body. The physical properties of Eureka and its comparatively short dynamical lifetime rise the question for its origin.

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Another possible Martian Trojan has been discovered.
Ephemeris:
2001 DH47 a,e,i = 1.52, 0.03, 24 q = 1.4708
Date TT R. A. (2000) Decl. Delta r Elong. Phase V
2007 07 29 21 20.65 +04 04.3 0.590 1.567 154.0 16.5 19.6
2007 08 08 21 10.03 -01 57.3 0.567 1.569 165.6 9.2 19.3
2007 08 18 20 58.87 -08 44.2 0.568 1.572 167.2 8.2 19.2
2007 08 28 20 49.62 -15 20.7 0.595 1.573 156.3 15.0 19.6
2007 09 07 20 44.18 -21 01.1 0.644 1.575 143.9 22.2 20.0
2007 09 17 20 43.57 -25 25.6 0.711 1.576 132.5 28.0 20.4
2007 09 27 20 47.96 -28 35.1 0.791 1.576 122.6 32.4 20.7
2007 10 07 20 56.82 -30 40.0 0.878 1.577 114.1 35.4 21.1
2007 10 17 21 09.46 -31 51.4 0.970 1.576 106.5 37.3 21.3
2007 10 27 21 25.12 -32 18.9 1.064 1.576 99.9 38.4 21.6
2007 11 06 21 43.06 -32 09.9 1.158 1.575 93.9 38.9 21.8

2007 11 16 22 02.71 -31 29.9 1.250 1.573 88.5 38.9 21.9


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A new space rock has been found that devotedly travels around with Mars as it orbits the Sun, bringing the total number of such 'groupies' to four. But astronomers say it was Mars not its tiny companions that originally insinuated itself into the rock group billions of years ago.
The asteroid, called 2007 NS2, was discovered by astronomers at the La Sagra Observatory in southern Spain on 16 July. Based on its brightness, it is estimated to be about 1 kilometre across.

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Ed ~ The rock was discovered on the 14th

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