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Chapter 6 The Earth and Moon

Chapter 6 The Earth and Moon. Distance between Earth and Moon has been measured to accuracy of a few centimeters using lasers (at McDonald Observatory). Orbital Properties. Moon. Mercury. Earth. Radius. 1700 km. 1440 km. 6380 km. Mass. 7.3 × 10^22 kg. 3.3 × 10^23 kg. 6.0 × 10^24 kg.

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Chapter 6 The Earth and Moon

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  1. Chapter 6The Earth and Moon

  2. Distance between Earth and Moon has been measured to accuracy of a few centimeters using lasers (at McDonald Observatory) Orbital Properties

  3. Moon Mercury Earth Radius 1700 km 1440 km 6380 km Mass 7.3 × 10^22 kg 3.3 × 10^23 kg 6.0 × 10^24 kg Density 3300 kg/m3 5400 kg/m3 5500 kg/m3 Escape Speed 2.4 km/s 4.3 km/s 11.2 km/s Physical Properties

  4. Moon has large dark flat areas, due to lava flow, called maria (early observers thought they were oceans) Surface Features on the Moon

  5. Moon also has many craters (from meteorite impacts) Surface Features on the Moon

  6. Surface Features on the Moon Far side of Moon has some craters but no maria

  7. Surface Features on the Moon Cratering on Mercury is similar to that on Moon

  8. Moon is tidally locked to Earth—its rotation rate is the same as the time it takes to make one revolution, so the same side of the Moon always faces Earth Rotation Rates

  9. Soviets had first contact with Moon: • First spacecraft to fly past Moon: January 1959 • First spacecraft to (crash) land on Moon: September 1959 • First pictures of far side of Moon: October 1959 • The United States is (so far) the only country to send people to the Moon: • First person on Moon: July 1969 • Last person on Moon: December 1972 Lunar Exploration

  10. Air molecules have high speeds due to thermal motion. If the average molecular speed is well below the escape velocity, few molecules will escape. • Escape becomes more probable: • For lighter molecules (higher speed for same kinetic energy) • At higher temperatures • For smaller planets (escape speed is less) More Precisely : Why Air Sticks Around

  11. Molecules in a gas have a range of speeds; the fastest (and those that are headed in the right direction) will escape More Precisely : Why Air Sticks Around

  12. Meteoroid strikes Moon, ejecting material; explosion ejects more material, leaving crater Lunar Cratering and Surface Composition

  13. Craters are typically about 10 times as wide as the meteoroid creating them, and twice as deep • Rock is pulverized to a much greater depth • Most lunar craters date to at least 3.9 billion years ago; much less bombardment since then Lunar Cratering and Surface Composition

  14. The Bombardment Era & the Nice Model The era 3.9 billion years ago saw impacts everywhere in the inner SS. The most accepted explanation is called the Nice Model - Jupiter and Saturn switched orbital positions and perturbed the asteroid and comet belts.

  15. Craters come in all sizes, from the very large… Lunar Cratering and Surface Composition

  16. …to the very small Lunar Cratering and Surface Composition

  17. Regolith: Thick layer of dust left by meteorite impacts Lunar Cratering and Surface Composition Moon is still being bombarded, especially by very small “micrometeoroids”; softens features

  18. Meteorites also hit Earth; this crater is in Arizona: Lunar Cratering and Surface Composition

  19. More than 3 billion years ago, the moon was volcanically active; the rille here was formed then: Lunar Cratering and Surface Composition

  20. Recent lunar missions have been smaller, cheaper, and less complex, but still yield fruitful results. Here, images of the Moon’s south pole, from Clementine (cost $70 million): Discovery: The Moon on a Shoestring

  21. Moon’s density is relatively low, and it has no magnetic field—cannot have sizable iron/nickel core Interior Crust is much thicker than Earth’s

  22. Current theory of Moon’s origin: Glancing impact of Mars-sized body on the still-liquid Earth caused enough material, mostly from the mantle, to be ejected to form the Moon Computer model: The Origin of the Moon

  23. Time before present: Event: 4.6 billion yr Formation of Moon; heavy bombardment liquefies surface 3.9 billion yr Bombardment much less intense; lunar volcanism fills maria 3.2 billion yr Volcanic activity ceases Evolutionary History of the Moon

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