Open AccessObliquity variations due to climate friction on Mars: Darwin versus layered models
Author(s) -
Spada Giorgio,
Alfonsi Laura
Publication year - 1998
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/98je02495
Subject(s) - mars exploration program , geology , flattening , lithosphere , mantle (geology) , tidal acceleration , viscoelasticity , geophysics , planet , physics , paleontology , astrobiology , astrophysics , thermodynamics , astronomy , tectonics
In response to periodic variations in the obliquity, giant CO 2 ice caps may form in the polar regions of Mars. The delayed response of the equatorial bulge of Mars to these periodic loads may introduce a secular term in the time evolution of the obliquity. Up to now, the variations in the flattening of Mars induced by the polar ice caps have been estimated using the Darwin model, which simply consists of a uniform sphere with Newtonian rheology. For Earth‐like viscosities of ∼3×10 21 Pa s the Darwin model maximizes the friction and predicts a secular obliquity variation comparable to the currently observed value (∼24°). Our main purpose here is to address the role of two well‐recognized features of Mars (a thick lithosphere and a core) on the response of its equatorial bulge and thus on the secular changes of obliquity driven by climate friction. This is done using a layered model with Maxwell viscoelastic rheology. We show that for a wide range of admissible mantle viscosities the obliquity variation is sensibly smaller (by a factor of ∼2) than the one predicted by the Darwin model. On the basis of this finding, we can rule out the possibility that the present‐day obliquity of Mars totally results from climate friction.