Title: On the impact origin of Phobos and Deimos III: resulting composition from different impactors,
Abstract: 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' moons in this framework
is missing. The chemical composition of Phobos and Deimos is unconstrained. The
large uncertainty 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' surface make the determination of their
composition very difficult from 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-,
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 Phobos and Deimos as result of the accretion
and mixing of dust and solids, we find that the derived assemblage (dust rich
in metallic-iron, sulphides and/or carbon, and quenched solids rich in
silicates) can be compatible with the observations. The JAXA's MMX (Martian
Moons eXploration) mission will investigate the physical and chemical
properties of the Maroons, 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.