pic/puzzle of the day & announcements for nov 3, 2008 quiz #4: wednesday other: office hours...
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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
1. Geology of Mercury & Venus
2. Venusian Atmosphere
3. Earth vs. Venus - This planet is TOO HOT
Today:
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
Mercury in the Sky
•Closest Planet to the Sun•Hard to observe
What time of day is Mercury observable?
Mercury - Early Observations
Giovanni Schiaparelli(1835-1910)
•Closest Planet to the Sun•Hard to observe (imagination required!)
• Mercury Rotates Slowly
•Synchronous?•T?
Mercury - Synchronous Rotation?
1965 - Dyce & PettengillDOPPLER EFFECT
How??
1962 - Radiation from Mercury not so cold
X
Not Synchronous
Mercury - Synchronous Rotation?
1965 - Dyce & PettengillRotation Period = 59 Days(Orbital Period = 88 Days)
1962 - Radiation from Mercury not so cold
X
Not Synchronous
How long is a day on Mercury?
1 day on Mercury = 176 Earth daysLonger 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)
Mercury & Einstein
Observation: Mercury’s Orbit Precesses
General Relativity!Space is curved by Sun’s mass!WHY??
?
Mercury - OverviewPlanet of Extremes
Distance36 million miles (0.39
AU)Closest Planet to Sun
Orbital Period 88 daysRotation Period
59 days 3:2 Resonance - Tides!
Radius 2440 km (0.38 Earth)Smallest Planet (no
Pluto)
Mass3.3 x 1023 kg (0.055
Earth)Least Massive
Density 5.4 g/cm3 Densest except Earth - Iron
Surface T800 F (day), -290 F
(night)Atmosphere Essentially none
Magnetic Field small but present! Surprising - why??Axis Tilt 0 degrees seasons?
Mercury - Spacecraft dataMariner 10: Venus/Mercury flyby (1974)
Flew by 3x before it ran out of fuel!
Imaged 45% of surface
Calculated HIGH density
(4.4g/cm3)Large iron coreSmall Magnetic
Field (1% Earth)
Mercury’s Magnetic Field - Why?Small Magnetic
Field (1% Earth)
2007 - Mercury has a small molten core!
Mercury - Spacecraft dataMessenger - Recent close approach Feb. 1 & Oct. 6, 2008!
Mercury orbit - March 18, 2011
Messenger Terrain
South Pole
Messenger Terrain - Similar to Moon!
QuickTime™ and aH.264 decompressor
are needed to see this picture.
Mercury - Surface FeaturesHeavily Cratered Areas - Old (Heavy
Bombardment)Large smooth Basins - Younger, Lava from Large impacts?
Mercury - Surface Features
Messenger Images
Mercury - Surface Features
-size of Texas-jumbled terrain opposite-caused by large impact
Caloris Basin - largest feature on Mercury
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
Mercury - Unsolved Mysteries
- “Mysterious dark blue material??”
-Ice on Poles?
-size of molten core?