Nonlinear Sciences – Chaotic Dynamics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dda....39.1402c&link_type=abstract
American Astronomical Society, DDA meeting #39, #14.02
Nonlinear Sciences
Chaotic Dynamics
Scientific paper
Despite recent theoretical advances (Gomes et al. 2005, Chambers 2007) the cause of the Late Heavy Bombardment (a.k.a. Lunar Cataclysm) is still controversial. During the LHB, which ended by 3.8 Gya (with no clear start date; Chapman et al. 2007) multiple large impact basins formed on the Moon, and there is some evidence of bombardment on Earth, Mars and Vesta. While leading theories prefer late depletion of the main asteroid belt, trace element data in lunar soils point to overwhelmingly enstatite chondrite impactors, usually associated with the inner solar system. Bottke et al.(2007) have shown that even high-inclination planet-crossing planetesimals decay too fast to be a viable source of the LHB. However, there exist several stable niches, potentially relevant to the LHB. We show that putative Vulcanoids and Earth-Mars-belt asteroids (Evans and Tabachnik 1999) are not plausible sources of the LHB, and that the apparent complete depletion of those regions is likely due to YORP and Yarkovsky effects, rather than any purely dynamical causes. The region between Mars and the asteroid belt does offer a long-term refuge, the stability of which depends crucially on the long-term behavior of Mars's eccentricity (cf. Chambers 2007). If Mars originally had a more circular orbit (long term e < 0.09), small bodies could survive in this region until chaotic dynamics excites martian eccentricity (Laskar 1989, 2008). This scenario is very similar to the "Planet V" hypothesis (Chambers 2007), only that the planet never formed. The amount of mass required for the LHB is roughly similar to that of the asteroid belt, implying much higher small-body density in the transmartian region. This is still a negligible fraction of the material needed to form the inner planets, and would require that this region was not swept by the nu6 secular resonance, unlike the main belt.
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