On the Impact Origin of Phobos and Deimos. III. Resulting Composition from Different Impactors

Francesco C. Pignatale1, Sébastien Charnoz1,2, Pascal Rosenblatt3,4, Ryuki Hyodo5, Tomoki Nakamura6, and Hidenori Genda5

Astrophysical Journal 853, 118 Link to Article [DOI: 10.3847/1538-4357/aaa23e]
1Institut de Physique du Globe de Paris (IPGP), 1 rue Jussieu, F-75005, Paris, France
2Institut de Physique du Globe/Universite Paris Diderot/CEA/CNRS, F-75005 Paris, France
3Royal Observatory of Belgium, Avenue circulaire 3, B-1180 Uccle, Belgium
4Now at ACRI-ST, 260 route du pin-montard-BP 234, F-06904 Sophia-Antipolis Cedex, France
5Earth-Life Science Institute/Tokyo Institute of Technology, 152-8550 Tokyo, Japan
6Tohoku University, 980-8578 Miyagi, Japan

The origin of Phobos and Deimos in a giant impact-generated disk is gaining larger attention. Although this scenario has been the subject of many studies, an evaluation of the chemical composition of the Mars’s moons in this framework is missing. The chemical composition of Phobos and Deimos is unconstrained. The large uncertainties about the origin of the mid-infrared features; the lack of absorption bands in the visible and near-infrared spectra; and the effects of secondary processes on the moons’ surfaces make the determination of their composition very difficult using remote sensing data. Simulations suggest a formation of a disk made of gas and melt with their composition linked to the nature of the impactor and Mars. Using thermodynamic equilibrium, we investigate the composition of dust (condensates from gas) and solids (from a cooling melt) that result from different types of Mars impactors (Mars-, CI-, CV-, EH-, and comet-like). Our calculations show a wide range of possible chemical compositions and noticeable differences between dust and solids, depending on the considered impactors. Assuming that Phobos and Deimos resulted from the accretion and mixing of dust and solids, we find that the derived assemblage (dust-rich in metallic iron, sulfides and/or carbon, and quenched solids rich in silicates) can be compatible with the observations. The JAXA’s Martian Moons eXploration (MMX) mission will investigate the physical and chemical properties of Phobos and Deimos, especially sampling from Phobos, before returning to Earth. Our results could be then used to disentangle the origin and chemical composition of the pristine body that hit Mars and suggest guidelines for helping in the analysis of the returned samples.

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