Martian paleoclimates
1er octobre 2002
On Earth, the coring of the ice polar caps allowed to recover the signature of the climate evolution over more than 400 000 years with great precision, and to establish their correlation with the variation of the insolation on Earth’s surface resulting from planetary perturbations (Petit et al., Nature, 399, 429, (1999)). On Mars, it is still impossible to core the ice caps as it was successfully done on Earth. Nevertheless, the pictures of the crevasses of the martian ice caps taken by the Mars Global Surveyor high resolution camera show enough details to allow for the first time to correlate the insolation variations on the martian surface with the observed stratification of the ice caps.
Since the first image of the Viking spacecrafts revealed the stratification of the martian ice caps, it was assumed that the observed layers result from climatic variations on the planet surface, but the quality of the pictures was not sufficient to allow for a precise correlation between the observed data and the computation of the insolation variation on the martian surface. The mechanism governing the accumulation of these ice layers are also very uncertain and many orders of magnitude still remained in the estimated accumulation rates of the layers. The high resolution pictures of the Mars Global Surveyor camera present now enough details to allow for a refined study of these layers (Figure 1).
Figure1. Image of the martian
North polar cap taken by the wide field camera of Mars
Orbital Camera (MOC). The crevasses on the ice caps are
layered with white and darker bands visible on the images
taken by the high resolution camera. Here,the image
M00-2100 was taken on April 13, 1999. The precise origin
of these layers is still uncertain, but it is very likely
that they result from the strong climatic variations on
Mars surface, the darker bands corresponding to higher
density of dust.
Image : NASA/JPL/Malin Space Science Systems
Figure1. Image of the martian
North polar cap taken by the wide field camera of Mars
Orbital Camera (MOC). The crevasses on the ice caps are
layered with white and darker bands visible on the images
taken by the high resolution camera. Here,the image
M00-2100 was taken on April 13, 1999. The precise origin
of these layers is still uncertain, but it is very likely
that they result from the strong climatic variations on
Mars surface, the darker bands corresponding to higher
density of dust.
Image : NASA/JPL/Malin Space Science Systems As for the Earth, the planetary perturbations lead to long period variations of the martian orbital elements and tilt of the spin axis (also called obliquity). On Earth, the obliquity variations are of 1.3 degrees around its mean value (23.3 degrees), but according to Milankovitch theory of paleoclimates, these variations are sufficient to induce large variations of the summer insolation in high latitudes on the Earth surface (at the limit of the ice caps) that are at the origin of the ice ages of the quaternary. On Mars, the orbital and obliquity variations are much larger than on the Earth (Figure 2). The group of the Institute of Celestial Mechanics (Paris Observatory), in collaboration with a researcher from Brown University, was able to establish for the first time a correlation between the observed variations of the luminosity of the ice cap layers and the computed variations of the insolation on the martian surface, resulting from planetary perturbations. These results allow to propose that the more recent 250 m of the ice cap were accumulated in 500 000 years, corresponding to a mean deposition rate of 0.05 cm/year.
Figure2. Variations of Mars
obliquity (angle between the planet equator and orbital
plane), eccentricty, and summer insolation at the north
pole surface, computed over 10 million years. These
variations result from the gravitational planetary
perturbations exerted by the other planets of the solar
system.
Figure2. Variations of Mars
obliquity (angle between the planet equator and orbital
plane), eccentricty, and summer insolation at the north
pole surface, computed over 10 million years. These
variations result from the gravitational planetary
perturbations exerted by the other planets of the solar
system. Jacques Laskar , Benjamin Levrard (Observatoire de Paris, France), John Mustard (Brown University, USA).
Reference : J. Laskar, B. Levrard, J. Mustard, " Orbital forcing of the martian layered deposits", Nature, 26 septembre 2002
Contact
Jacques Laskar (Observatoire de Paris, IMCCE)
Dernière modification le 4 mars 2013