Transcript The Moon
Phases and Appearance Ground Based Observations Moon has light and dark areas on it Light and dark not randomly distributed There are a few bright “craters” with rays What is the origin of the craters? Volcanic or Impact? What are the dark areas – reflectivity similar to basalt on the Earth. Until we physically go there, we won’t know anything. An impact crater is An explosive event similar To a volcanic crater. Ejecta blanket (rays) only Real ground based evidence That craters are due to impact Central Peak = Impact Let’s Go There (42 years ago!) Mercury program: This was a single astronaut program designed at determining if successful earth orbit could be achieved. This program lasted 2 years (1961--1963) and saw 7 flights. Gemini Program These spacecraft were manned by two astronauts. The program was designed to test the endurance of astronauts in space (the longest Gemini mission was 14 days) as well as the ability to rendezvous and dock with another spacecraft. This program lasted 1.5 years (1965--1966) and saw 10 flights. It remains NASA's most aggressive mission. Apollo Program These spacecraft were manned by three astronauts. This was the lunar landing program. The initial launch of Apollo 7 in October 1968 was to check out the spacecraft over a 10 day mission. Two months later, during Christmas of 1968, Apollo 8 went to the moon and achieved a lunar orbit and returned to the Earth. Apollo 8 remains the most symbolic of all our trips into space as, for the first times, photographs of the blue earth rising about another object were seen. Space Ship Earth Where to Safely Land? Lunar Dune Buggy There really is no atmosphere Science Goal Bring Rocks back Age date them Landings in the Lunar Highlands (bright regions) and lunar maria (dark regions) were necessary for this. Altogether 6 successful landings and rock retrieval were enough. 4 Geological Events The moon solidified and cooled 4.4 billion years ago Between 4.4 and 4.2 billion years an intense period of bombardment occurred from the material that was left over from the accretion process. Most of this material was chunks of rock less than 10 km in size. Similar debris reigned down on the surfaces of Mercury, Venus, Earth and Mars. Since the moon is not geologically active, this record of bombardments is maintained on its surface. Formation of Maria At 3.9 billion years there was another period of bombardment which involved a few large (> 100 km) pieces of debris. The earth acted as a gravitational focusing mechanism which caused most of these impacts to occur on the side of the moon always facing the earth (there are no lunar Maria on the far side of the moon). These large impacts produced the lunar Maria. This was a severe shock to the crust of the moon and over time, molten basalt would flow out of the deep fissures and cracks in the crust that were caused by the initial impact. This took 200 million years to occur and is the last geological process which occurred on the moon (3.7 billion years ago) Are we done now? NO, turns out we can’t figure out (until recently) the actual origin of the moon. Simple Density argument. Planetary Formation Process If the Moon formed like the Earth It should have formed out of the same raw material It should have the same bulk density as the Earth Earth = 5.5 g/cc but Moon is 3.3 g/cc Yikes – where the heck did it come from? Three Ideas Formed in place but Earth “stole” the Iron from the forming moon ridiculous Formed near Mars (whose density is 3.3) and found its way here yeah, how? Fission off from the Earth yeah right, how does that work? Okay, all ideas don’t work, why is it there? Fission does work! Note density of Earth’s mantle is 3.3: Moon Formed by Unusual Process Used to be very close to the Earth (1000 times closer than now!) Huge tidal inland lakes (may have helped with development of early life) Tidal force slows down the daily rotation of the Earth and causes the moon to get farther away (current rate is 3.8 cm per year) The moon Next time you look Up at Moon, Remember, it might Be the essential Reason Life could form on The earth