On the impact origin of Phobos and Deimos III: resulting composition from different impactors

TL;DR

This study explores how different impactors could have contributed to the composition of Phobos and Deimos, using thermodynamic models to predict their chemical makeup and inform future sample analysis by the MMX mission.

Contribution

It provides the first detailed thermodynamic analysis linking impactor types to the moons' potential compositions, aiding interpretation of upcoming sample data.

Findings

Wide range of possible compositions depending on impactor type

Dust rich in metallic-iron, sulphides, or carbon can match observations

Impacts produce distinguishable chemical signatures in dust and solids

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.