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International audience; We analyzed multiple asteroid systems observations collected with SPIFFI/SINFONI, a spectro-imager equipped with an adaptive optics system (AO) mounted on one of the Very Large Telescope. Our goal is to constrain the formation mechanisms of these systems by comparative spectroscopy analysis. H K spectro-images (from 1.45 to 2.45 um) of the similarly-sized Trojan asteroid (617) Patroclus-Menoetius taken on June 16 2009 revealed that the two components separated by ~0.35' have identical reflectance spectra within 8% with a flux ratio of 0.95 in agreement with their expected size ratio (Mueller et al. Icarus 2010). Careful analysis of H K observations of the triple asteroids (45) Eugenia (2010-08-27) and (87) Sylvia (2010-07-27) showed the presence of the outermost moons of these systems. The innermost moons, which are closer and fainter, are not detected. The position of the Petit-Prince, moon of (45) Eugenia, is in agreement with our dynamical model based on our genetic algorithm assuming a purely Keplerian orbit (see Vachier et al. A&A 2013) developed including 43 AO observations collected from Nov. 1998 to Aug. 2010. After extracting the spectra of the moons using different algorithms, we noticed a reddening of the moons in comparison with their primary with a slope ratio of ~1.7 and ~1.0 for Eugenia and Sylvia respectively. This is a surprising result since no significant differences between the moon and primary of the M-type (22) Kalliope (Laver et al. Icarus, 2009) and the C-type (379) Huenna (DeMeo et al. Icarus 2011) have been reported so far. It is difficult to explain the source of the difference in spectral reflectance between the components of the C-type (45) Eugenia and X type (87) Sylvia systems without having a clear understanding of surface alteration processes on low-albedo asteroids. Lantz et al. (A&A 2013) favored space weathering to explain the bluing effect of Ch/Cgh asteroids as compared with CM meteorites. Assuming that we detected the same effects on these asteroids, it will imply that the primary surface is younger that the satellite one. Future efforts in laboratory simulations and sample return missions should focus on determining the composition and alteration of carbonaceous asteroids.

International audience; Since their discovery less than 10 years ago, ~200 known multiple asteroid systems have been studied with a combination of observing techniques, including adaptive optics, lightcurve photometry, and mid-infrared spectrophotometry. Those observations show that ~15 large (D>100km) asteroids that are known to possess km-sized satellite(s) (22 Kalliope, 45 Eugenia, 87 Sylvia, 93 Minerva, 216 Kleopatra, ...) share common orbital characteristics, implying a common formation scenario: e.g. catastrophic disruption or ejection after an oblique impact. More than 70 smaller (10-15km) binary asteroid systems have been detected through anomalies in their lightcurves and are believed to have formed by fission due to the YORP effect. By comparison with meteorite analog densities, mid-IR data reveal that these systems have a significant porosity (larger than 30%) implying a rubble-pile interior. We will review these key results and discuss their implications for the interior of asteroids in the light of recent space mission results. Future explorations using new ground-based facilities and space mission concepts will be also discussed. This work is supported by the NSF grant AAG-0807468 and NASA grant NNX11AD62G

International audience; (45) Eugenia and its satellites are one of the few triple asteroid systems discovered. Eugenia's shape is far from spherical, with a theoretical J2 estimated to 0.19 assuming an homogenous distribution of mass in its interiour. We have adapted the numerical model we developped for Pluto's system to Eugenia's case, adding the second harmonics of Eugenia's gravity field. Previous study by [4] found a lower value of the coefficient J2. We present here our results after fitting the satellites observations to our model using new observations of the system done in 2010 . We confirm that the value of J2 is about three times lower than its theoretical value. We find a similar pole direction for Eugenia and similar orbital elements for Petit-Prince.