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Anhydrous pyroxene-rich interplanetary dust particles (IDPs) have beenproposed as surface analogs for about two-thirds of all C-complex asteroids.However, this suggestion appears to be inconsistent with the presence ofhydrated silicates on the surfaces of some of these asteroids including Ceres.Here we report the presence of enstatite (pyroxene) on the surface of twoC-type asteroids (Ceres and Eugenia) based on their spectral properties in themid-infrared range. The presence of this component is particularly unexpectedin the case of Ceres because most thermal evolution models predict a surfaceconsisting of hydrated compounds only. The most plausible scenario is thatCeres' surface has been partially contaminated by exogenous enstatite-richmaterial, possibly coming from the Beagle asteroid family. This scenarioquestions a similar origin for Ceres and the remaining C-types, and it possiblysupports recent results obtained by the Dawn mission (NASA) that Ceres may haveformed in the very outer solar system. Concerning the smaller C-types such asEugenia, both their derived surface composition (enstatite and amorphoussilicates) and low density suggest that these bodies accreted from the samebuilding blocks, namely chondritic porous, pyroxene-rich IDPs and volatiles(mostly water ice), and that a significant volume fraction of these bodies hasremained unaffected by hydrothermal activity likely implying a late accretion.In addition, their current heliocentric distance may best explain the presenceor absence of water ice at their surfaces. Finally, we raise the possibilitythat CI chondrites, Tagish Lake-like material, or hydrated IDPs may berepresentative samples of the cores of these bodies.

Different origins or different evolutions? Decoding the spectral diversity among C-type asteroids