Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.1203w&link_type=abstract
American Astronomical Society, DPS meeting #40, #12.03; Bulletin of the American Astronomical Society, Vol. 40, p.405
Astronomy and Astrophysics
Astronomy
Scientific paper
The Moon's formative period is thought to have ended 4.4Gyr ago, however the largest impact basins on the Moon were probably formed some 500-600 Myr later during a particularly intense cratering epic (known informally as the Late Heavy Bombardment - or LHB). The LHB impactor population is commonly thought to have come from the asteroid belt or the outer Solar System, suggesting that the LHB was a System-wide phenomenon affecting all of the terrestrial planets. Here we consider an alternative explanation: that the LHB impactors may have originally been bound to the Earth, orbiting in a region of stability between 20 and 50 R⊕ beyond the young Moon. We suppose here that the outer material was debris produced by the Moon-forming collision and captured into stable near- circular orbits beyond the Moon, possibly through gas drag in an impact-generated nebula surrounding the Earth. Only 0.1 Mmoon of material is needed in this region to produce the largest basins on the lunar surface, assuming 1% impact efficiency. For this material to be a viable candidate population responsible for the LHB, orbits in the region 20 and 50 R⊕ must be dynamically stable for timescales >10-100 Myr, long enough for the Moon to tidally evolve into this region from 5 - 10 R⊕ where it was born. Here we show the results of several 1-Myr integrations of 500 massless moonlets orbiting in the region 20 and 50 R⊕, with the Moon at different distances from the Earth. Naturally there is some dynamical excitation and erosion of the particle disk, but many of the particles remain on stable low-eccentricity trajectories for the length of the integrations suggesting that a circumplanetary population of moonlets beyond the Moon could have been responsible for the LHB affecting the Earth-Moon system.
Carlisle A. W.
Williams Darren M.
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