Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons

Pascal Rosenblatt (1) , Sébastien Charnoz (2, 3) , Kevin M. Dunseath (4) , Mariko Terao-Dunseath (4) , Antony Trinh (1) , Ryuki Hyodo (3, 5) , Hidenori Genda (6) , Stéven Toupin (1)

1 ROB - Royal Observatory of Belgium = Observatoire Royal de Belgique
2 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
3 IPGP - Institut de Physique du Globe de Paris
4 IPR - Institut de Physique de Rennes
5 Kobe University
6 ELSI - Earth-Life Science Institute [Tokyo]

Phobos and Deimos, the two small satellites of Mars, are thought either to be asteroids captured by the planet or to have formed in a disc of debris surrounding Mars following a giant impact. Both scenarios, however, have been unable to account for the current Mars system. Here we use numerical simulations to suggest that Phobos and Deimos accreted from the outer portion of a debris disc formed after a giant impact on Mars. Larger moons are formed from the denser inner disc and migrate outwards due to gravitational interactions with it. The resulting orbital resonances spread outwards and gather the dispersed debris, facilitating accretion into two satellites of sizes similar to Phobos and Deimos. The larger inner moons fall back to Mars after about 5 million years due to the tidal pull of the planet, after which the two outer satellites evolve into Phobos- and Deimos-like orbits. Our results clarify why Mars has two small satellites instead of one large moon. Our model predicts that Phobos and Deimos are composed of a mixture of material from Mars and the impactor.

Mots clés: Collisions

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Physique [physics]

Pascal Rosenblatt, Sébastien Charnoz, Kevin M. Dunseath, Mariko Terao-Dunseath, Antony Trinh, et al.. Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons. Nature Geoscience, 2016, 9 (8), pp.581. ⟨10.1038/ngeo2742⟩. ⟨hal-01350105⟩