On the long term evolution of the spin of the Earth.
Abstract
Laskar and Robutel (1993Natur.361..608L) have globally analyzed the stability of the planetary obliquities in a conservative framework. Here the same model is extended by adding dissipative effects in the EarthMoon system: the body tides and the friction between the core and the mantle. Some constraints on the poorly known coefficients of dissipation are determined with the help of paleogeological observations. One consequence is that the scenario proposed by Williams (1993, EarthScience review, 34, 1) for the past history of the Earth's obliquity seems unlikely. A synthesis of 500 numerical integrations of the EarthMoon system with orbital perturbations for the next 5Gyr is presented. It is shown that the time scale of the dissipative effects is long enough to induce an adiabaticlike evolution of the obliquity which is driven in the chaotic zone within 1.5 to 4.5Gyr. A statistical study of possible evolutions conducted with a tidal dissipation coefficient dt of 600 seconds demonstrated that 68.4% of the trajectories attained an obliquity larger than 81 degrees, with a maximum of 89.5 degrees.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 1997
 Bibcode:
 1997A&A...318..975N
 Keywords:

 EARTH;
 CHAOS;
 INSTABILITIES;
 CELESTIAL MECHANICS