Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p52a0363l&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P52A-0363
Other
3344 Paleoclimatology, 3346 Planetary Meteorology (5445, 5739), 5450 Orbital And Rotational Dynamics, 5462 Polar Regions, 6225 Mars
Scientific paper
Since the first images of polar regions of Mars revealed alternating bright-dark layers there has been speculation that their formation is tied to the orbital forcing of climate, but uncertainties of more than two orders of magnitude remained in the deposition time scale. We have analyzed the profile of radiance extracted from MOC image M00-02100. The layers evident in this image are representative of one long trough in the northern cap located near 279°W 86°N from which several other MOC images were acquired and show a consistent stratigraphy over a strike of more than 100 km. A very apparent feature in this profile is the presence of three nearly identical cycles (N1,N2,N3), on top of which are some higher frequency variations. As the time scale for the accumulation of these layers is very poorly constrained, we have searched for the best fit with the insolation variations deduced from a new solution for the orbital and spin evolution of Mars, including all 9 main planets, the Moon as a separate object, Earth and solar oblateness, and the effect of general relativity. The obliquity and precession of Mars axis were computed using initial conditions deduced from the Pathfinder mission. The main uncertainty in the obliquity solution arises from the initial precession frequency (p=-7.576 +/- 0.035 arcsec/year) (Folkner et al., 1997). Despite Mars obliquity is chaotic, the chaotic behavior of the solution becomes only significant beyond 10Ma, and we found that all solutions within the precession uncertainty lead to a large increase of obliquity after 5 Ma. We have used this constraint to exclude the possibility that the observed cycles (N1,N2,N3) are related to the large ≈ 2.4 Ma eccentricity modulation, and assume that they are more closely related to the climatic precesion and obliquity cylces. We thus obtain for the best fit, an average deposition rate of 0.05 cm/yr for the most recent 250 m thick deposit of the North ice polar cap. Ref. Laskar, J., Levrard, B., Mustard, J.F. : 2002, Orbital forcing of the martian polar layered deposits, Nature, in press
Laskar Jacques
Levrard Benjamin
Mustard John F.
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