Over time, tides have the following effects on the Earth and the Moon• Slowing the Earth’s rotation - the day is increasing by 0.002 sec/century.•Increasing the size of the Moon’s orbit - its distance from the Earth is increasingby 4 cm/year (≈2 inch/year)• The moon istidally lockedto the Earth -the sameside of the moon is always facing us (moon rotationperiod is the same as its orbital period)
Lunar Surface-lack of atmosphere and water preserves surface featuresMaria– mantle material•“seas” - darker areas resultingfrom earlier lava flow•Basaltic, iron rich, high density(3300 kg/m3).Highlands– crust material•elevated many km above maria•Aluminum rich, low density (2900kg/m3).
Craters•Caused by meteoroid impactsCaused by meteoroid impacts•Pressure to the lunar surface heats the rock andPressure to the lunar surface heats the rock anddeforms the grounddeforms the ground•Explosion pushes rock layers up and outExplosion pushes rock layers up and out•TheTheejecta blanketejecta blanketsurrounds the cratersurrounds the crater•The rate of cratering on the moon is determined fromThe rate of cratering on the moon is determined fromthe known ages of the highland and maria regions.the known ages of the highland and maria regions.•The Moon (and solar system?) experienced a sharpThe Moon (and solar system?) experienced a sharpdrop in the rate of meteoritic bombardment about 3.9drop in the rate of meteoritic bombardment about 3.9billion years ago (end of accretion era)billion years ago (end of accretion era)•The rate of cratering has been roughly constant sinceThe rate of cratering has been roughly constant sincethat timethat time
Formation of the Moon•Mars-sized body hit theMars-sized body hit themolten Earthmolten Earth•Parts of the mantle blew offParts of the mantle blew offand later formed the moonand later formed the moon•Earth had differentiated, soEarth had differentiated, sothe mantle (from which thethe mantle (from which theMoon formed) was alreadyMoon formed) was alreadymetal poor.metal poor.The Moon has an overall composition and density quite difference from theThe Moon has an overall composition and density quite difference from theEarth, but which resembles the material in the Earth’s mantle.This observationEarth, but which resembles the material in the Earth’s mantle.This observationhas led to the Impact Theory for the formation of the Moon.has led to the Impact Theory for the formation of the Moon.
The Terrestrial Planets
Mercury•Mercury is not tidally locked toMercury is not tidally locked tothe sun in the same way as thethe sun in the same way as themoon-earth systemmoon-earth system•Sun’s gravity and Mercury’sSun’s gravity and Mercury’seccentric orbit brought it intoeccentric orbit brought it intosemi-synchronous orbitsemi-synchronous orbit•Mercury presents the sameMercury presents the sameface to the sun every OTHERface to the sun every OTHERtime around (rotational periodtime around (rotational periodis 59 days and orbital period isis 59 days and orbital period is88 days)88 days)•Old surface with no apparent plate tectonicsOld surface with no apparent plate tectonics•Craters flatter and have thinner ejecta rims than lunar craters due toCraters flatter and have thinner ejecta rims than lunar craters due tohigher gravity on Mercury than the moon
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