The Origins and Geological Histories of Deimos and Phobos: Hypotheses and Open Questions

Igneous processes in the small bodies of the Solar System II: Small satellites and dwarf planets

“…Their respective average radii are 6.12 km 78 and 10.7 km, 79 and their respective average bulk densities are ≈1.48 and 1.876 g cm −3 . 80 The latter value of 1.876 g cm −3 is an adjustment with respect to previous Viking measurements in which both satellites were assessed having essentially the same density of 1.9–2.0 ± 0.6 g cm −3 . 81 , 82 , 83 Their irregular shapes and their spectroscopic characteristics are similar to those of D-type asteroids, 84 , 85 or Amalthea, 44 which are mostly located in the outer AB and in the outer Solar System.…”

“… 97 For this reason, moons formed from an earlier and primordial circum-Martian accretion disk (i.e., not formed by impact) would have had even less chance to survive. 80 At last, an additional hypothesis based on the splitting of a progenitor moon into two has been also suggested. 98 , 99 …”

The importance of Phobos simulants: a review on our current knowledge

“…After years of exploring Mars, the origin and evolution of Phobos and Deimos remain unknown. Understanding their origin may provide constraints on the formation and early dynamical environment of Mars (see, e.g., Ramsley and Head, 2021). To explain the origin of the Martian Moon system, several hypothesis have been presented: the recycling hypothesis, the hypothesis that Phobos and Deimos were once a single large Moon that later split, the hypothesis in which the moons are captured small bodies from the asteroid belt or outer Solar System (capture scenario), or the hypothesis in which they are reaccreted impact ejecta from Mars (in situ formation or giant impact scenario).…”