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Pic/Puzzle of the Day & Announcements for Nov 3, 2008 Quiz #4: Wednesday Other: Office hours today, until 3 (other by appt) Guest Lecture on Mars! (Wednesday/Monday) HW4 solns: Posted later today
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1. Geology of Mercury & Venus 2. Venusian Atmosphere 3. Earth vs. Venus - This planet is TOO HOT Today:
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Mercury - An “Extreme” Planet Closest Planet to the Sun 0.38 AU, 2.5 x closer than Earth sunlight is 6.25 x more intense! Highest Density other than Earth Largest Temperature Swings more than 1000 F! Interesting Rotation Global Magnetic Field
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Mercury in the Sky Closest Planet to the Sun Hard to observe What time of day is Mercury observable?
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Mercury - Early Observations Giovanni Schiaparelli (1835-1910) Closest Planet to the Sun Hard to observe (imagination required!) Mercury Rotates Slowly Synchronous? T?
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Mercury - Synchronous Rotation? 1965 - Dyce & Pettengill DOPPLER EFFECT How?? 1962 - Radiation from Mercury not so cold X Not Synchronous
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Mercury - Synchronous Rotation? 1965 - Dyce & Pettengill Rotation Period = 59 Days (Orbital Period = 88 Days) 1962 - Radiation from Mercury not so cold X Not Synchronous
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How long is a day on Mercury? 1 day on Mercury = 176 Earth days Longer than 1 year! Earth rotates on its axis ~365 times for each revolution around the Sun Mercury rotates on its axis exactly 1.5 times for each revolution around the Sun (3:2 spin-orbit resonance) Rotation Period = 59 Days (Orbital Period = 88 Days)
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Mercury & Einstein Observation: Mercury’s Orbit Precesses General Relativity! Space is curved by Sun’s mass! WHY?? ?
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Mercury - Overview Planet of Extremes Distance36 million miles (0.39 AU)Closest Planet to Sun Orbital Period88 days Rotation Period59 days3:2 Resonance - Tides! Radius2440 km (0.38 Earth) Smallest Planet (no Pluto) Mass 3.3 x 10 23 kg (0.055 Earth) Least Massive Density5.4 g/cm 3 Densest except Earth - Iron Surface T 800 F (day), -290 F (night) AtmosphereEssentially none Magnetic Fieldsmall but present!Surprising - why?? Axis Tilt0 degreesseasons?
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Mercury - Spacecraft data Mariner 10: Venus/Mercury flyby (1974) Flew by 3x before it ran out of fuel! Imaged 45% of surface Calculated HIGH density (4.4g/cm 3 ) Large iron core Small Magnetic Field (1% Earth)
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Mercury’s Magnetic Field - Why? Small Magnetic Field (1% Earth) 2007 - Mercury has a small molten core!
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Mercury - Spacecraft data Messenger - Recent close approach Feb. 1 & Oct. 6, 2008! Mercury orbit - March 18, 2011
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Messenger Terrain South Pole
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Messenger Terrain - Similar to Moon!
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Mercury - Surface Features Heavily Cratered Areas - Old (Heavy Bombardment) Large smooth Basins - Younger, Lava from Large impacts?
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Mercury - Surface Features Messenger Images
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Mercury - Surface Features -size of Texas -jumbled terrain opposite -caused by large impact Caloris Basin - largest feature on Mercury
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Mercury - Surface Features -3 km high -100s of km across -contraction from cooling (planet shrank by ~20km!) -closed off volcanic vents Scarps: Large cliffs caused by contraction of surface
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Mercury - Unsolved Mysteries - “Mysterious dark blue material??” -Ice on Poles? -size of molten core?
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