Dynamical sequestration of the Moon-forming impactor in co-orbital resonance with Earth

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2016-09, Vol.275, p.239-248
• Main Authors: Kortenkamp, Stephen J., Hartmann, William K.
• Format: Article
• Language: English
• Subjects: Computer simulation; Delay; Earth; Impactors; Mathematical models; Moon; Orbital resonances (celestial mechanics); Planetary dynamics; Planetary formation; Terrestrial planets; Venus (planet)
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2016.04.007

•We explore Earth's co-orbital resonance as a potential source of the Moon-forming impactor.•Mars-mass co-orbital companions of Earth at 1 AU can persist for up to 250 Million years.•Escaping companions can impact Earth, with an average impact time of 101 Million years.•Several models resulted in formation of a super-Earth, with at least Earth and Venus colliding.•Configurations that remained stable included unusual hierarchical coorbital systems. Recent concerns about the giant impact hypothesis for the origin of the Moon, and an associated “isotope crisis” may be assuaged if the impactor was a local object that formed near Earth. We investigated a scenario that may meet this criterion, with protoplanets assumed to originate in 1:1 co-orbital resonance with Earth. Using N-body numerical simulations we explored the dynamical consequences of placing Mars-mass companions in various co-orbital configurations with a proto-Earth of 0.9Earth-masses (M⊕). We modeled 162 different configurations, some with just the four terrestrial planets and others that included the four giant planets. In both the 4- and 8-planet models we found that a single Mars-mass companion typically remained a stable co-orbital of Earth for the entire 250million year (Myr) duration of our simulations (59 of 68 unique simulations). In an effort to destabilize such a system we carried out an additional 94 simulations that included a second Mars-mass co-orbital companion. Even with two Mars-mass companions sharing Earth's orbit about two-thirds of these models (66) also remained stable for the entire 250Myr duration of the simulations. Of the 28 2-companion models that eventually became unstable 24 impacts were observed between Earth and an escaping co-orbital companion. The average delay we observed for an impact of a Mars-mass companion with Earth was 102Myr, and the longest delay was 221Myr. In 40% of the 8-planet models that became unstable (10 out of 25) Earth collided with the nearly equal mass Venus to form a super-Earth (loosely defined here as mass ≥1.7M⊕). These impacts were typically the final giant impact in the system and often occurred after Earth and/or Venus has accreted one or more of the other large objects. Several of the stable configurations involved unusual 3-planet hierarchical co-orbital systems.