270 SOLAR SYSTEM/Moon Table Continued Name Tycho Vendelinus Walter Wargentin Zucchius Latitude 43.4 16.4 33.1 49.6 61.4 S S S S S Longitude 11.1 61.6 1.0 60.2 50.3 W E E W W Diameter, km 102 131 128 84 64 Southern highlands; brightest ray centre Petavius chain Trio with Regiomontanus and Purbach Schickard area; the famous plateau Schiller area; pair with Segner Figure Astronaut Schmitt, of Apollo 17, standing by a huge boulder Schmitt was a professional geologist who had been trained as an astronaut specially for the mission; December 1972, He and his companion, Eugene Cernan, are (so far) the last men to have been to the Moon Courtesy of NASA material within it as clasts – granulites and igneous rocks of anorthosite, gabbronorite and troctolite composition, also minor dunite and pyroxenite A unique Al-rich orthopyroxenite/Al-spinel clast is compatible with pressure at a depth of $20 km within the lunar crust at its source Origin of the Craters It was long believed that the craters were of volcanic origin, similar in type to terrestrial calderæ, but it is now widely accepted that the vast majority are of impact origin, and we have at least a reasonable idea of the sequence of events When the Moon came into existence as a separate body, the heat generated melted the outer layers, and for a time there must have been a magma ocean many kilometres deep Eventually, a crust was formed, thicker on the far side of the Moon than on the Earth-facing side; by cosmic standards it did not take long for the axial rotation to become synchronous At that stage there was a vast amount of debris moving round the Sun, and the newly-formed planets and satellites swept it up Between 4400 and 3900 Figure The minerals of the Moon This is a mosaic of 53 images, obtained in 1992 by the Galileo space craft The exagger ated false colour shows the differences in surface structure Blue to orange indicate volcanic lava showing the dark blue Mare Tranquillitatis (lower left) is rich in titanium Near the bottom of the image, right at Mare Tranquillitatis, is Mare Crisium, pink colours indicating material of the lunar highlands million years ago came the Great Bombardment, when meteorites rained down on the Moon to produce the first major basins such as the Mare Tranquillitatis Then, between 3900 and 3800 million years ago, came the tremendous impact which resulted in the Imbrian basin and affected the whole of the Moon As the Great Bombardment ceased there was widespread vulcanism, with magma pouring out from below the crust and flooding the basins to produce structures such as the Mare Orientale The lava flows ended rather suddenly; as the outpouring slackened, many craters were left undamaged, so that the youngest, such as Tycho and Copernicus, are unflooded On the far hemisphere, with its thicker crust, there was less flooding, which explains the absence of major Maria and the presence of large,