Climate Simulations of Mars at Low Obliquity
L.Lange, F.Forget, R.Vandemeulebrouck, E.Millour, A.Spiga, A.Bierjon, A.Delavois, J.Naar, Laboratoire de
Météorologie Dynamique, Institut Pierre-Simon Laplace (LMD/IPSL), Sorbonne Université, Centre National de
la Recherche Scientifique (CNRS), École Polytechnique, École Normale Supérieure (ENS), Paris, France
lucas.lange@lmd.ipsl.fr

Introduction:
In some high latitude craters, intriguing moraines
are interpreted to have been formed by by CO2 ice
glacier flows [1]. These glaciers might when Mars
obliquity was low and the local climate was colder
[1]. The obliquity of Mars Mars obliquity reached
values ~15° nearly 800,000 years ago , and probably
less than a few degrees during the Amazonian era
[2]. The climate of Mars at such low obliquities has
been little studied, but it suggests that the atmosphere could totally collapse into CO2 glaciers,
leaving behind a residual atmosphere of only Ar and
N2, but 20 times less dense than today [3,4,5]. We
present here preliminary results of our climate simulations of Mars at low obliquity using the LMD
Mars Global Climate Model [6].
Planetary Evolution Model:
Low obliquity periods last generally tens of thousands of years [Laskar]. It is therefore impossible to
study such long-period with the classic GCM. We
therefore built a new tool called « Planetary Evolution Model » to simulate the evolution of the climate
over long time-steps. This model has been validated
by comparing its results with the ones of LMD GCM
long-runs made at low obliquity (e.g., Fig. 1).
Slope parametrization in the GCM:
The LMD GCM used for the current Mars climate
study {Forget1999} cannot be used directly to study the
formation and evolution of CO2 glaciers on slopped terrain. Indeed, the typical resolution is about 300 km in
longitude and 220 km in latitude. However, the moraines
observed in {KRESLAVSKY2011} are rather of the order
of one km. We introduced in the LMD GCM a detailed

parametrization of the topography distribution at
kilometer scale. This parameterization enables to
model the microclimate on local slopes and thus the
formation of CO2/H2O glaciers. This parametrization has been tested and validated using the current
observations of ice deposits on pole facing slopes
(Vincendon).

Simulation parameters:
Two set of simulations are presented below. In
the first one, the opacity of the atmosphere is fixed,
and we only consider two tracers in the atmosphere:
one called CO2 and the other one called noCO2. Water is not modeled here. Based on the work of
[CO2ice], we assume that the CO2 ice thickness can
not excessed 10 m on slopes, and must flows if this
thickness is reached. This simulation is noted S1.
In the second one, the opacity of the atmosphere

follows the nominal dust scenario provided with the
MCD (milour, Montabone). The main tracers are
CO2, dust, and water. The same conditions for
glacial flow than those described for S1 are used.
Values of albedo, emissivity for CO2 and H2O
ices, as well as ice tables are set to the current values
used in the LMD GCM. The obliquity of the simulations is set arbitrary to 5°.
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