Transcript The moon
The moon As seen through a telescope General features • The Moon (and other bodies) were originally thought to have an atmosphere • And living beings (selenites on the Moon) • Therefore, it was assumed that water and land existed • Easy to see on the Moon • Names of features go back to 17th C Lunar oceans • Mare (singular), maria (plural) – Dark – Smooth – Low – Often circular – Often large (Imbrium ~1100 km) – Therefore, they had to be water Highlands • • • • • Lighter in color (reflectivity/albedo) Rough High (as much as 25,000 ft) Irregular in shape Thought to be the continental areas Minor features • Craters – Microscopic to few hundreds of km – Many clearly visible by naked eye – Seen by Galileo – Named after scientists, philosophers of antiquity (and others) • Valleys – In the highlands – Not common Minor features • Rilles – Sinuous • Like empty river beds – Straight • Long linear valleys • Rays – Bright streaks radial to craters – Small to large Minor features • Regolith – Lunar soil – Gravelly – Difficult to see real bed rock Gross features – Earth –Density 5.5 –Gravity 1 –Escape V. 11.2 –(Km/sec) Moon 3.34 1/6 2.4 First (Serious) Study of Moon • • • • 1962 Shoemaker and Hackmann Shoemaker – geologist Hackmann – geographer Assumption – Maria formed by enormous impacts – Law of superposition holds for the Moon – Mare material is basalt lava Law of superposition • Simple case – sedimentary rocks Cross-section of sedimentary rocks A B C C is the oldest A is the youngest Application to impact Before impact A surface rim ejecta B ejecta is younger than that on which it lies two impacts C 1 2 the ejecta blanket from 1 lies on top of the ejecta blanket from 2. 1 is therefore younger S and H chose • Mare Imbrium – Northeast part of the near side – Large circular mare – Surrounded by mountains Maria on the near-side of the Moon Immediate vicinity of Mare Imbrium Procedure • Isolate the area including M Imbrium • And the surrounding region – Specifically – Copernicus – Eratosthenes • Determine the sequence of events Time • Absolute – Specify the age in time units – Example: the Onondaga limestone was formed 380 million years ago • Relative – Specify the age in non-time units – Example: the Edwardian age in England – The Elizabethan age Argument • M. Imbrium was formed by impact • Created ejecta blanket • If Copernicus was older, it would have been buried • But Copernicus is visible • Therefore, Copernicus is younger than the impact that formed M. Imbrium • Further, M. Imbrium is filled with lava • Therefore, the lava came after the impact that formed M. Imbrium • Copernicus is situated on some of the mare material • Therefore, Copernicus is younger that the lava Chronology of the Moon • Sequence of events • The time units are named (relative time) • Names are taken from the feature in question • Thus, the crater Copernicus was created in Copernican time (note the different spelling)