SCI238 Lecture Notes - Lecture 10: Blueshift, Planetary Migration, Oort Cloud
9 Jul 2013
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Document Summary
Mars lacks an ozone layer, so much of the sun"s damaging ultra- violet radiation passes unhindered to the surface. The lunar maria are generally circular because they are essentially flooded craters (and craters are almost always round). Their dark color comes from the dense, iron-rich rock (basalt) that rose up from the lunar mantle as molten lava. The most surprising features of mercury are its many tremendous cliffs evidence of a type of past tectonics quite different from anything we have found on any other terrestrial world. They probably formed when tectonic forces compressed the crust, causing the surface to crum- ple. Because crumpling would have shrunk the portions of the surface it affected, mercury as a whole could not have stayed the same size unless other parts of the surface expanded. Early in its history, mercury"s larger size and greater iron content allowed it to gain more internal heat from accre- tion and differentiation than did the moon.
