The Moon: The View From Earth Recall the moon exhibits synchronous rotation, where its rotation period on its axis is equal to its revolution period around the Earth. 27.3 days sidereal month Believed to have a slower rotation period, however Earth’s tidal forces on the moon are so strong, it has slowed the moon so it now rotates once each orbit. A moon whose rotation is locked to its planet is said to be tidally coupled. Only 12 people have stood on the moon, but planetary astronomers know it well. Photographs, measurements, and samples paint a picture of an airless, ancient, battered crust, and a world created by a planetary catastrophe.
The Moon: A View From Earth Escape velocity on the moon is too low to keep gas atoms and molecules from escaping into space. Cannot see clouds or other obvious traces of an atmosphere, and shadows near the terminator, the dividing line between daylight and darkness, are sharp and black. No air to scatter light and soften shadows. Clearly, the moon is an airless (therefore, soundless requires medium) world.
Lunar Surface Features Most of the moon is covered by highlands, which are areas of light-colored, mountainous terrain scarred by craters. No folded mountain ranges no plate tectonics. Mountains pushed up by millions of impact craters one on top of the other. Impossible to form a new crater without destroying the equivalent of an old one.
Lunar Surface Features The lowlands of the moon are smooth, dark plains called maria, Latin for “seas”. Galileo believed them to be water originally. Further observations showed they were marked by ridges, faults, smudges, and scattered craters, thus could not be water. Ancient lava flows shortly after formation. Long, winding channels called rilles, are often found near the edges of maria and are further evidence for past lava flows.
Formation of Maria Impacts of heavy meteorites early on broke the moon’s crust, producing deep basins that were filled with lava as it oozed out.
0 Terrain opposite to Mare Imbriumis jumbled by seismic waves from the impact ~ 1000 km (700 mi) Formation of Maria
Impact Cratering The craters covering the moon, and many other bodies in the solar system, were produced by the high-speed impact of meteorites of all sizes known as impact cratering. Debris blasted out of a crater is called ejecta, and it falls back to blanket the surface around the crater. Ejecta shot out along specific direction can form bright rays.
Impact Cratering It is difficult to estimate the true age of any specific crater, however you can find the relative ageof a lunar rock by noting a crater or its rays partially cover other craters clearly the crater on top is younger. Can be calibrated using radioactive ages of lunar samples, which indicates the cratering rate decreased when the moon was young. Combining all of this information, astronomers can estimate the absolute age, in years, of various moon rocks. Maria containing few craters ~ 3-4 billion years. Highlands ~ 4+ billion years.
Impact Cratering Rate of impacts due to interplanetary bombardment decreased rapidly within the first 500 million years after the solar system formation.
The age of moon rocks provide evidence of a late heavy bombardment about 4.1 to 3.8 billion years ago.
The Apollo Missions May 25, 1961 President John F. Kennedy committed the United States to landing a human being on the moon by 1970 in a speech to congress. Later, gave speech at Rice University in 1962.
Challenges Getting There No atmosphere on the moon to disturb the trajectory of the spaceship. Needed to carry enough fuel for: In-flight corrections Descent to lunar surface Re-launch from surface Return trip to Earth Also needed to carry enough food supply to last a week. Solution take 2 spaceships, leave behind unnecessary items. One to make round-trip One to land on the moon’s surface
Challenges Getting There Command module was the long-term living space and command center for the trip. 3 astronauts had to live in it for a week. Had to carry all the life-support equipment, navigation instruments, computers, power packs, and so on for the week. Lunar module was attached to the front of the command module (“Eagle”). Carried only enough fuel and supplies for the short trip to the lunar surface.
History of the Moon Our natural satellite, the moon, is about 1/4 the diameter of Earth. Much of what we know about the moon comes from the Apollo missions. Six Apollo spacecraft landed on the moon between 1969 and 1972. Gravitational attraction at the lunar surface is 1/6 of that experienced on Earth’s surface. Example: 150 lb. person on Earth weighs only 25 lb. on the moon.
The Eagle Has Landed The first manned mission to successfully land on the moon was the Apollo 11mission (July 20, 1969) This mission carried three astronauts: Neil Armstrong, Buzz Aldrin, and Michael Collins. Of those 3, only 2 walked on the moon (Armstrong first, then Aldrin). Collins stayed in the command module. This fulfilled President John F. Kennedy’s mission.
Apollo 17 Landing: Taurus-Littrow Lunar Highlands Apollo 11 Landing: Sea of Tranquility Lunar Maria
380 kg (840 lb) of lunar rocks and soils collected between 1969-1972.
History of the Moon Evidence suggests the moon must have formed from a molten-like state. Heavy rocks sink to bottom, lighter rocks stay at surface. No magnetic field. Small core is believed to exist containing small amounts of metallic iron (Fe). Surface believed to have solidified 4.1 – 4.6 BYA. Then underwent a heavy bombardment period for the next 500 million years.
Origin of the Moon
Most widely accepted theory for the origin of the moon is when the solar system was forming, an object the size of Mars impacted the Earth.
This is known as the Giant Impact Hypothesis.
Impact heated the material enough to melt it.
Tiny particles of debris went into orbit around the Earth; eventually accreted together and formed the moon.