Challenges in Forming Phobos and Deimos Directly from a Splitting of an Ancestral Single Moon

Abstract The origin and evolution of Martian moons have been intensively debated in recent years. It is proposed that Phobos Deimos may originate directly from the splitting an ancestral moon orbiting at around synchronous orbit. At this hypothetical splitting, apocenter inner (presumed as Phobos) pericenter outer Deimos) would coincide, that, their semimajor axes reside inside outside orbit with nonzero eccentricities, respectively. However, successive orbital two not studied. Here, we perform direct N -body integrations moons, including oblateness J 2 4 terms. We show while they precess, likely collide within ∼10 yr impact velocity v imp ∼ 100–300 m s −1 (∼10–30 times moons’ escape velocity) isotropic direction. occurs respectively, where timescale periodic alignment regulated by precession. By performing additional simulations, such a high-velocity results disruptive outcome, forming debris ring orbit, which several small accrete. Such evolutionary path eventually form different system one see today. Therefore, it seems unlikely are split single moon.