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Laboratoire des sciences de la Terre (URA 726 ENS Lyon et UCB Lyon I), Ecole Normale Supérieure de Lyon, 46 allée d’Italie, 69364 Lyon cedex 07, France
Impact craters are the only universal drills to probe planetary lithospheres. The relationship of the lithospheric thickness/crater diameter ratio and the morphology of the outer parts of the crater are controlled by the rheology of the target. These relationships indicate the following: (1) The lithosphere is thicker on silicated bodies than on icy bodies of the same size. (2) The lithosphere is thicker on small planetary bodies than on larger ones. (3) There is a secular lithospheric thickening and a planetary cooling for silicated and icy bodies. (4) Because of the thickness and the continuity of the lithosphere of one-plate planets, local mechanical disturbances may be transmitted over a long distance and may affect the entire planet. (5) Thermal properties of the lithospheres of satellites are incompatible with the chondritic abundance of radioactive nucleids. This indicates that the origin of satellites is more complex than the accretion-collision of chondritic/icy planetesimal swarms. (6) There is no direct relation between plate tectonics and lithospheric thickness. Some planets have (or have had) the same lithospheric thickness as the Earth, but have not developed plate tectonics. This indicates that plate tectonic development is controlled by parameters other than lithospheric thickness.
