2 The Lunar Surface Maria Highlands low density rocky slag formed on top of molten Moonheavily crateredMaria17% of Lunar surfaceHuge lava flows from volcanoesBasalts - similar to volcanic rock on Earthbut no waterfewer volatile (= easily melted) elements.Much less iron.
4 Craters as Chronometers The number of craters on a surface can be used to estimate its age: older surfaces have been exposed to impacts for longer and show more craters
5 Complications Any changes in the impactor population over time Secondary impacts formed by ejecta from a single large impactSaturation: when a surface is so heavily cratered that a new crater can form only at the expense of an older oneThere is a need for measured surface ages in order to calibrate the crater counting
13 Ages of lunar featuresHeavily cratered highlands: billion years oldLarge basins: 3.9 – 4.1 billion years oldMaria flooding: 3.0 – 3.9 billion years oldCompared to the Earth, the typical lunar surface is very ancient
15 Late heavy bombardment? A proposed interval about 3.8 to 4 billion years ago in which the moon and the inner solar system were subjected to heavy asteroid bombardmentTime of the formation of impact basins?
20 The Interior of the Moon Most maria are on near side.Center of mass offset 2 km towards Earth.EarthCrust is 107 km thick on far side.Crust ~ 0 km thick on near side.From Modern Astrophysics, by Carroll & Ostlie.3476 kmGeologically inactive.No magnetic field no molten core.