Linda A. Hinnov
Professor of Geology
Department of Atmospheric, Oceanic and Earth Sciences
George Mason University

Paleoastrodynamics

At present, high-accuracy Solar System numerical modeling is limited to 50 Ma. Cyclostratigraphy is the only hope for deciding which, if any, model is valid for times prior to 50 Ma. The 405-kyr orbital eccentricity cycle is stable over hundreds of millions of years owing to the great mass of Jupiter. Nonetheless, modest changes to model initial conditions produce 405-kyr cycles with different phases, which can be compared to 405-kyr cycle phasing in cyclostratigraphy constrained by high-precision geochronology. If the 405-kyr phasing problem can be solved then accurate Earth-Mars orbital parameters can be reconstructed with confidence, opening the way for a comprehensive understanding of ancient Solar System dynamics.

Two significant orbital motions of Earth and Mars manifest as modulations in the Earth's orbital eccentricity and obliquity variations. Over the past 50 Ma, these modulations maintained 2:1 secular resonance and a libration state between the Earth and Mars orbits. Prior to 50 Ma, modeling indicates that the two orbits chaotically transitioned through circulation states and 1:1 secular resonance. The precise evolution cannot be determined numerically. Cyclostratigraphy must be consulted to constrain the history.

The plan is to compile Earth's long-term orbital eccentricity and inclination history from cyclostratigraphy. The results will be used to guide Solar System models on the timing and duration of Earth-Mars orbital transitions and resonance states, and to explore the orbital evolution of Jupiter, Saturn and Venus.