Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dda....37.1301c&link_type=abstract
American Astronomical Society, DDA meeting #37, #13.01; Bulletin of the American Astronomical Society, Vol. 38, p.674
Astronomy and Astrophysics
Astronomy
Scientific paper
To study the fate of possibly-resonant debris in the early Earth-Moon system, we constructed a numerical integrator capable of simulating all aspects of the system's tidal evolution. We confirm (Canup et al. 1999) that bodies in exterior resonances are unstable, but find that tadpole orbits are generally long-lived, with eccentricities that decrease during outward evolution. Our integrations start with the Moon on a circular orbit at 5 Earth-radii with 11 degree inclination wrt Earth's equator. We also assume that the Lunar eccentricity tides dominated over dissipation in early Earth. When tides cause the Moon to spiral out to a distance of about 38-39 R_E, all the trojans escape due to an apparent resonance with the Sun. We identify this perturbation as the evection resonance (i.e. trojan orbital pericenters precessing once per year). Depending on the exact initial conditions the difference between the lifetimes of various trojans can be as large as 10% (with no significant asymmetry between L4 and L5) thus yielding two 'escape events' separated in time by up to hundred million years.
A Q value of 90 for early Earth would result in the trojan escape to be about 3.9 Byr ago, coincident with the epoch of the "Lunar Cataclysm" (Tera et al 1974). We thus propose that the cataclysm was caused by fragments of the two ecaping Lunar trojans, which tidally disrupted and then collided with the Moon and Earth. The time spread of impacts from each of the two escape events would have been very brief (years for direct impacts, Myrs for impacts by bodies that escaped into heliocentric orbit). Uncertainties in the formation times of Lunar basins are sufficiently large that two distinct intense episodes may be consistent with the available cosmochemical chronology data.
Cuk Matija
Gallant Joseph
Gladman Brett J.
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