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!

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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?