HR: 16:30h
AN: P32C-03 INVITED     [PDF]
TI: The Formation of Martian Gullies by Near-Surface Ice Melting During Recent Periods of High Obliquity: Evidence from Gullies Distribution and Orientations
AU: * Mangold, N
EM: mangold@geol.u-psud.fr
AF: Universit\'{e} Paris-Sud, Bat 509 Orsayterre, Orsay, 91405 France
AU: Costard, F
EM: fcostard@geol.u-psud.fr
AF: Universit\'{e} Paris-Sud, Bat 509 Orsayterre, Orsay, 91405 France
AU: Forget, F
EM: forget@lmd.ens.fr
AF: Universit\'{e} P. & M. Curie, Laboratoire de M\'{e}t\'{e}orologie Dynamique, Jussieu, 75005 France
AB: We have performed a detailed statistical analysis of the gullies distribution and orientations as observed in the most recent MOC pictures (M01 to E18). It confirms the distribution of gullies poleward of about 30$^{o}$ of latitude with poleward-facing slopes preferred. This agrees with our calculations showing that the only places on Mars where the daily mean temperature has been above the melting point of water during the past obliquity cycles are the mid and high latitudes above 30$^{o}$, especially on poleward-facing slopes. The fact that poleward-facing slopes receive more sunlight and get warmer at high obliquity in the summer is due to the pole being tilted toward the sun, i.e. in the southern hemisphere around summer solstice, the sun appears most of the time in the southern sky. The distribution also shows a decrease of the number of gullies with the increase of latitude which is likely due to the decrease of the number of steep slopes ($>$25$^{o}$) at high latitudes. Indeed, as observed on the Earth, gullies are initiated by wet landslides called debris flows, which form mainly at steep slopes. Thus, the hypothesis of formation of Martian gullies by recent near-surface ice melting during periods of higher obliquity shows a strong consistency between climate modeling, distribution of Martian gullies and terrestrial analogs.
DE: 5415 Erosion and weathering
DE: 6207 Comparative planetology
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting