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Journal Articles The Astronomical Journal Year : 2017

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

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P. Vernazza
P. Beck
  • Function : Author
J. Emery
R. Brunetto
M. Marsset
L. Jorda
F. Borondics
  • Function : Author

Abstract

Anhydrous pyroxene-rich interplanetary dust particles (IDPs) have been proposed as surface analogs for about two-thirds of all C-complex asteroids. However, this suggestion appears to beinconsistent with the presence of hydrated silicates on the surfaces of some of these asteroids, including Ceres. Here, we report the presence of enstatite (pyroxene) on the surface of two C-type asteroids (Ceres and Eugenia) based on their spectral properties in the mid-infrared range. The presence of this component is particularly unexpected in the case of Ceres, becausemost thermal evolution models predict a surface consisting of hydrated compounds only. The most plausible scenario is that Ceres' surface has been partially contaminated by exogenous enstatite-rich material, possibly coming from the Beagle asteroid family. This scenario questions a similar origin for Ceres and the remaining C-types, and it possibly supports recent results obtained by the Dawn mission (NASA) that Ceres may have formed in the very outer solar system. Concerning the smaller D∼200 km C-types such as Eugenia, both their derived surface composition (enstatite and amorphous silicates) and low density (<1.5 g cm −3) suggest that these bodies accreted from the same building blocks, namely chondritic porous, pyroxene-rich IDPs and volatiles (mostly water ice), and that a significant volume fraction of these bodies has remained unaffected by hydrothermal activity likely implying a late accretion. In addition, their current heliocentric distance may best explain the presence or absence of water ice at their surfaces. Finally, we raise the possibility that CI chondrites, Tagish-Lake-like material, or hydrated IDPs may be representative samples of the cores of these bodies.
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hal-01790534 , version 1 (13-05-2018)

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P. Vernazza, J. Castillo-Rogez, P. Beck, J. Emery, R. Brunetto, et al.. DIifferent origins or different evolutions? Decoding the spectral diversity among C-type asteroids. The Astronomical Journal, 2017, 153 (2), ⟨10.3847/1538-3881/153/2/72⟩. ⟨hal-01790534⟩
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