Climatic variations on Mars: 1. Astronomical theory of insolation

Abstract

This paper describes variations in the solar insolation on Mars that result from oscillations of the orbital eccentricity (0.005 ≲ e ≲ 0.141) and the obliquity (14.9° ≲ θ ≲ 35.5°) of the planet. Changes in the eccentricity and obliquity are produced by gravitation perturbations from the sun and the other planets, and a detailed account of the time evolution of these quantities is given. Particular attention is paid to the obliquity oscillations, which exert a strong influence on the climate of Mars. Changes in the earth's obliquity (Δθ ≈ 2°) are also calculated, and its behavior is contrasted with that of Mars. Equations for the average daily and yearly insolation as a function of latitude are derived, and several numerical examples are presented to illustrate the sensitivity of these quantities to the evolving dynamic parameters. Although the eccentricity produces important north-south seasonal asymmetries, a change in the obliquity causes a strong latitudinal redistribution of the solar insolation. Especially noteworthy is the fact that the yearly insolation at the poles of Mars varies by over 100% between the extremes of the obliquity range.