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Published byBuck McLaughlin Modified over 8 years ago
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The Moon and Mercury
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Distance between Earth and Moon measured accurately using lasers Viewed from Earth, Mercury is never far from the Sun Orbital Properties
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MoonMercuryEarth Radius1700 km1440 km6380 km Mass7.3 × 10 22 kg3.3 × 10 23 kg6.0 × 10 24 kg Density3300 kg/m 3 5400 kg/m 3 5500 kg/m 3 Escape Speed 2.4 km/s4.3 km/s11.2 km/s Physical Properties
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Maria - large dark flat areas, due to lava flow Early observers thought they were oceans Surface Features on the Moon and Mercury
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Many craters (from meteorite impacts) Surface Features on the Moon and Mercury
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Far side of Moon has some craters but no maria Surface Features on the Moon and Mercury
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Mercury cannot be imaged well from Earth; best pictures are from Mariner 10 Surface Features on the Moon and Mercury
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Cratering on Mercury is similar to that on Moon Surface Features on the Moon and Mercury
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Tidally locked to Earth Rotation rate is the same as the time it takes to make one revolution Same side of the Moon always faces Earth Moon’s Rotation Rates
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Thought to be tidally locked to the Sun Disproved in 1965 Mercury’s day and year are in a 3:2 resonance Rotates three times while going around the Sun twice. Mercury’s Rotation Rates
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Lunar Exploration Soviets had first contact with Moon: First spacecraft to fly past Moon: January 1959 First spacecraft to (crash) land on Moon: September 1959 (sigh) First pictures of far side of Moon: October 1959 United States the only country to send people to the Moon: First person on Moon: July 1969 Last person on Moon: December 1972
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Craters 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
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Meteoroid strikes Moon, ejecting material; explosion ejects more material, leaving crater Lunar Cratering and Surface Composition
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Craters come in all sizes, from the very large…
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Regolith: Thick layer of dust left by meteorite impacts Moon is still being bombarded, especially by very small “micrometeoroids”; softens features Lunar Cratering and Surface Composition
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Meteorites also hit Earth; this crater is in Arizona: Most famous in US (hint for exam) Lunar Cratering and Surface Composition
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More than 3 billion years ago, the moon was volcanically active; the rille here was formed then: Lunar Cratering and Surface Composition
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Mercury is less heavily cratered than the Moon Some distinctive features: Scarp (cliff), several hundred kilometers long and up to 3 km high The Surface of Mercury
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Caloris Basin, very large impact feature; weird terrain on opposite side of planet The Surface of Mercury
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“Weird terrain” is thought to result from focusing of seismic waves
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Moon’s density is relatively low, and it has no magnetic field—cannot have sizable iron/nickel core Crust is much thicker than Earth’s Interiors
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Mercury is much denser than the Moon and has a weak magnetic field—not well understood! Interiors
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Current theory of Moon’s origin: Glancing impact (Big Rock) of Mars-sized body on the still-liquid Earth Causing enough material, mostly from the mantle, to be ejected to form the Moon Computer model: The Origin of the Moon
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Time before present: Event: 4.6 billion yrFormation of Moon; heavy bombardment liquefies surface 3.9 billion yrBombardment much less intense; lunar volcanism fills maria 3.2 billion yrVolcanic activity ceases Evolutionary History of the Moon
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Mercury much less well understood: Formed about 4.6 billion years ago Melted due to bombardment, cooled slowly Shrank, crumpling crust Evolutionary History of Mercury
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Assignment R&D Questions –1,2,3,5,7,10,19
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