Reconceiling the orbital and physical properties of the martian moons

TL;DR

This paper proposes that Martian moons Phobos and Deimos likely formed from gas-to-solid condensation in an extended gaseous disk, reconciling their orbital and physical properties better than capture or co-accretion scenarios.

Contribution

It introduces a new formation model based on condensation in a gaseous disk, challenging previous theories and aligning spectral and physical properties of the moons.

Findings

Gas-to-solid condensation explains moon properties

Magma phase formation is unlikely for the moons

Capture scenario is less plausible based on spectral data

Abstract

The origin of Phobos and Deimos is still an open question. Currently, none of the three proposed scenarios for their origin (intact capture of two distinct outer solar system small bodies, co-accretion with Mars, and accretion within an impact-generated disk) is able to reconcile their orbital and physical properties. Here, we investigate the expected mineralogical composition and size of the grains from which the moons once accreted assuming they formed within an impact-generated accretion disk. A comparison of our results with the present day spectral properties of the moons allows us to conclude that their building blocks cannot originate from a magma phase, thus preventing their formation in the innermost part of the disk. Instead, gas-to-solid condensation of the building blocks in the outer part of an extended gaseous disk is found as a possible formation mechanism as it does allow reproducing both the spectral and physical properties of the moons. Such a scenario may finally reconcile their orbital and physical properties alleviating the need to invoke an unlikely capture scenario to explain their physical properties.