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et al. ; Asteroid (2) Pallas is the largest main-belt object not yet visited by a spacecraft, making its surface geology largely unknown and limiting our understanding of its origin and collisional evolution. Previous ground-based observational campaigns returned different estimates of its bulk density that are inconsistent with one another, one measurement1 being compatible within error bars with the icy Ceres (2.16 ± 0.01 g cm−3)2 and the other3 compatible within error bars with the rocky Vesta (3.46 ± 0.03 g cm−3)4. Here we report high-angular-resolution observations of Pallas performed with the extreme adaptive optics-fed SPHERE imager5 on the Very Large Telescope. Pallas records a violent collisional history, with numerous craters larger than 30 km in diameter populating its surface and two large impact basins that could be related to a family-forming impact. Monte Carlo simulations of the collisional evolution of the main belt correlate this cratering record to the high average impact velocity of ~11.5 km s−1 on Pallas—compared with an average of ~5.8 km s−1 for the asteroid belt—induced by Pallas's high orbital inclination (i = 34.8°) and orbital eccentricity (e = 0.23). Compositionally, Pallas's derived bulk density of 2.89 ± 0.08 g cm−3 (1σ uncertainty) is fully compatible with a CM chondrite-like body, as suggested by its spectral reflectance in the 3 μm wavelength region6. A bright spot observed on its surface may indicate an enrichment in salts during an early phase of aqueous alteration, compatible with Pallas's relatively high albedo of 12–17% (refs. 7,8), although alternative origins are conceivable. ; Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.C-0074 (principal investigator: P.V.). This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with NASA. M.M. was supported by the National Aeronautics and Space Administration under grant number 80NSSC18K0849 issued through the Planetary Astronomy Program. This work was supported by the French Direction Générale de l'Armement (DGA) and Aix-Marseille Université (AMU). P.V., A.D. and B.C. were supported by CNRS/INSU/PNP. J.H., J.D. and P.S. were supported by the grant 18-09470S of the Czech Science Foundation and by the Charles University Research Programme number UNCE/SCI/023. M.Brož was supported by the grant 18-04514J of the Czech Science Foundation. E.J. is a F.R.S.-FNRS Senior Research Associate. The work of T.S.-R. was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 730890. ; Peer reviewed

Context. CM-like asteroids (Ch and Cgh classes) are a major population within the broader C-complex, encompassing about 10% of the mass of the main asteroid belt. Their internal structure has been predicted to be homogeneous, based on their compositional similarity as inferred from spectroscopy and numerical modeling of their early thermal evolution. Aims. Here we aim to test this hypothesis by deriving the density of the CM-like asteroid (41) Daphne from detailed modeling of its shape and the orbit of its small satellite. Methods. We observed Daphne and its satellite within our imaging survey with the Very Large Telescope extreme adaptive-optics SPHERE/ZIMPOL camera and complemented this data set with earlier Keck/NIRC2 and VLT/NACO observations. We analyzed the dynamics of the satellite with our Genoid meta-heuristic algorithm. Combining our high-angular resolution images with optical lightcurves and stellar occultations, we determine the spin period, orientation, and 3D shape, using our ADAM shape modeling algorithm. Results. The satellite orbits Daphne on an equatorial, quasi-circular, prograde orbit, like the satellites of many other large main-belt asteroids. The shape model of Daphne reveals several large flat areas that could be large impact craters. The mass determined from this orbit combined with the volume computed from the shape model implies a density for Daphne of 1.77 +/- 0.26 g cm(-3) (3 sigma). This density is consistent with a primordial CM-like homogeneous internal structure with some level of macroporosity (approximate to 17%). Conclusions. Based on our analysis of the density of Daphne and 75 other Ch/Cgh-type asteroids gathered from the literature, we conclude that the primordial internal structure of the CM parent bodies was homogeneous. ; ESO programs [281.C-5011, 099.D-0098, 199.C-0074(A)]; W.M. Keck Foundation; Paris Observatory; National Science Foundation; NASA; CNRS/INSU/PNP; Czech Science Foundation [18-09470S]; European Union's Horizon 2020 Research and Innovation Programme [687378]; Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) [FRFC 2.5.594.09]; University of Liege; Canadian Space Agency; National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program [NCC 5-538]; NASA [09-NEOO009-0001]; National Science Foundation [0506716, 0907766] ; Open access journal. ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.