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Mercury = Hermes Mythology • Planet Mercury, Element, Mercredi • God of Commerce, Messenger God, guide to Hades • Winged sandals and staff Mercury’s Orbit • Mercury never seen more than 28° from the sun • Revolves/orbits 0.4 AU from sun in 88 days • Rotates in 59 days (radar) • 3 Rotations to 2 revolutions • Resonance Mercury Differentiation • • • • Small mass high temperature=no air Most dense planet except Earth Iron core – 75% of radius Tiny magnetic field – slow rotation? Liquid core? • Melted - heat of formation & decay of radioactive elements Impact Craters • Heavy bombardment cratered surface • Strange dark rimmed crater • Crater with gullies run to/from Intercrater Plains • More craters than the Lunar Maria 3.5 Billion, but less than Highlands 4.5 Billion years Caloris Basin • Giant impact creates ringed basin • Later flooded by lava • Jumbled terrain on opposite hemisphere of planet • Mariner 10&MESSENGER Volcanism on Mercury • Volcanic vent is kidney shaped depression Lobate Scarps • When Mercury cooled it shrunk & surface wrinkles formed • Which pass through a previously (109 years) existing crater • Smooth plains and intercrater plains (similar to maria) not saturated with craters so must be younger than other areas Messenger on its way back to Mercury • Launched Aug04; loops around sun 15 times, Earth once, Venus twice and Mercury 3 times • Will finally orbit in 2011 Rotation of the Moon • Revolves & rotates on axis in 27.3 days – synodic=29.53d • Always keeping one side facing the Earth • Resonance due to tidal coupling Flooding of Basins by Lava • Lowlands = mare in blue 3.5 billion years old basalt • Heavily cratered highlands in green 4.5 billion years old • Farside of Moon has no Maria due to thicker crust Impact Crater Formation • • • • • Impactor has velocity 10 times rifle bullet Releases energy 10 times equal mass of dynamite Impactor vaporized when temperature reaches millions K Shock wave forms shocked quartz found only in impacts Rebound can launch rocks without destroying them Craters Copernicus and Tycho • • • • Moon is covered by craters of all sizes Highlands are saturated with craters Mare/lowlands have fewer craters so are younger Notice rays, ejecta blankets, secondary craters Largest Impacts - Mare Orientale • Mare = sea in Latin are sites of major impacts • Note: multiringed basin • Which flooded with basalt @ 3.5 billion years ago = volcanism Volcanism - Hadley Rille • 150km long, 1.5km across, 300meters deep • Formed by flowing lava 3.3 billion years ago No Atmosphere to Soften Shadows • No Atmosphere => no erosion by wind water • Escape velocity too low • Maximum temperature of 123C&min of -233C Only Erosion Is Slow Surface Evolution • Regolith is crushed rock/dust; covers surface to depth of a few meters • Erosion by micrometeorites, solar wind etc. • Breccias glued with glass from impacts Formation of the Moon • Fission – Protoearth spun so fast that the moon budded off - but wrong angular momentum • Coaccretion- formed near Earth from nebula - but no iron core and no volatiles • Capture- formed somewhere else- wrong oxygen isotopes + hard to capture + no iron or volatiles • Giant Impact- Earth hit by Mars sized asteroid • • • • • Formation of Moon by Giant Impactor Elapsed time is about a day; moon forms in a year Earth ends up spinning once in 5 hours, moon in low orbit Earth was differentiated so moon is made from mantle material Correct isotope ratio, no iron core, volatiles evaporate Robin Canup’s simulation “Eagle Has Landed” • Apollo 11 lands in Mare Tranquillitatis • Neil Armstrong and Buzz Aldrin • 20 July 1969 “One Small Step” Hammer and Feather • 6 Moon missions &12 astronauts • A week to get there • Apollo 12 and Surveyor 3 Young Drives Moon Rover Last Man on the Moon? Giant Impactor • Painting by Kaufmann • Problem of the low density of the Moon • Solved by Moon being formed from low density mantle material • Is it Science? Testable Prediction = Disprovable Fox TV • Moon Hoax• No stars: Not enough exposure Illuminated astronaut: bright background • Parallel shadows: topography • Flag waving: no atmosphere so waved longer & liked it wrinkled Precession of Mercury’s Orbit • Most of the precession is due to other planets • Part is due to General Relativity No Atmosphere = No Erosion But Ice at Mercury’s & Moon’s Poles? • • • • VLA radar observations see echo from poles which resembles ice Surface temperature 100K to 700K, but inclination of rotation axes 0º South Pole of Moon with craters permanently in shadow in white Hydrogen detected from neutron spectrometer on Lunar Prospector Lunar Impact