Stability Analysis Of The Martian Obliquity During The Noachian Period

Details Stability Analysis Of The Martian Obliquity During The Noachian Period Stability Analysis Of The Martian Obliquity During The Noachian Period

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.5101b&link_type=abstract

American Astronomical Society, DPS meeting #42, #51.01; Bulletin of the American Astronomical Society, Vol. 42, p.1069

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The obliquity of Mars is currently chaotic on a 100 Myr time scale, and it undergoes large-amplitude oscillations over 125 kyr. These cause long-term insolation differences across Mars' surface and appropriate changes in its climate.
The obliquity oscillations result from secular forcing by the other planets, which depend on the orbital properties of the latter. However, the secular architecture of the solar system was very different during Mars' Noachian era, before the Late Heavy Bombardment (LHB). The latter was probably caused by a dynamical instability of the giant planets leading to a violent evolution of mutual scattering ending with their current orbits. During the 500-600 Myr preceding the LHB the orbits of the giant planets were nearly circular, changing the forcing on Mars' obliquity.
Here numerical simulations of Mars' obliquity evolution for a solar system configuration prior to the LHB are presented. These include the expected orbits of the giant planets and a range of possible terrestrial planet orbits. Generally, for less excited terrestrial planet orbits and circular giant planets, it is found that one of the sources of chaos currently affecting Mars' obliquity has disappeared. The current resonances affecting the obliquity are generally narrower and shifted to higher obliquity by 10 deg. When the Angular Momentum Deficit (AMD) of the terrestrial planets, which measures the deviation of the system from circular and coplanar orbits, before the LHB is less than 70% of the current value, there is a significant range of initial obliquities which would have been stable, and where the short-term oscillation amplitude is lower than 20 deg. An unchanged AMD for the terrestrial planets before and after the LHB would have resulted in overlapping resonances, which are partially responsible for the chaotic evolution observed today. However, these resonances would have been located at a higher range of obliquities.

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