6

Planetary Geology

Planets Rock!

6

Goals

• What determines why planets look the way they do.

• What are the 4 main process that affect a planet’s surface.

• How does planetary interior affect planetary atmospheres?

6

Why are planets different?

• Different planets look different.

• What determines this?• To understand the outside,

you must understand the insides.

6

Concept Test

• The cores of the terrestrial worlds are made mostly of metal because ______. a. the terrestrial worlds as a whole are made

mostly of metal.b. the core contained lots of radioactive

elements that decayed into metals.c. over billions of years, convection gradually

brought dense metals downward to the core.

d. metals sunk to the centers a long time ago when the interiors were molten throughout.

e. None of the above.

6

Internal Heat• Why is heat the

driver of geological processes?

• What is heat?• Think of temperature

on an atomic scale.• Where do you expect

change?

6

Accretion• Planets form out of

primordial cloud of gas and dust.

• Atoms to dust to grains to rocks to asteroids to planetesimals to planets.

6

Differentiation

• Accreted material is all mixed.• Friction generates heat.

6

Lithosphere – Radius at which rock is too cool to flow by convection.

6

Concept Test

• Given this description of planetary interiors, we expect:a. Smaller planets should cool off faster than

bigger ones.b. Larger planets should have thinner

lithospheres than smaller planets.c. There should be fewer signs of geological

activity on the surfaces of smaller planets compared to larger ones.

d. All of the above.e. None of the above.

6

How do we know?• How do we know what is really going

on inside planets?1. Look for signs of surface activity. Has

anything changed recently?2. Look for magnetic fields around planet.

1. Fluid core2. Convection of fluid3. Rapid rotation

6

Comparative Planetology• 4 main surface altering processes

– Cratering (exogenic)– Volcanism (endogenic)– Tectonics (endogenic)– Erosion (endogenic)

• In order for endogenic processes to occur, energy must be available.

• Small planets (and moons, and asteroids) generally have little internal heat, and, therefore, little endogenic activity.

• Exogenic processes affect everything.

6

Volcanoes

6

Volcanoes

6

Tectonics

6

6Figure 9.13B

6

Plate Tectonics

6

Erosion

6

Alluvial Fan

6

Craters

6

New Surface vs. Old• Impacts happen over time.• Can date a surface by the number of

craters on its surface. Date since last geologic activity.

• Pot holes on road:– Many holes = old road.– Few holes = new road

• Resurfacing = energy– One or more endogenic

processes.• Another clue to insides.

6

Why is Earth so Different?• Why do we have oceans of water?• Why doe we have an atmosphere

with:– so little carbon dioxide?– so much O2 and N2?

6

Atmosphere Origins

• Outgassing• Volcanoes.• CO2 and H2O

main gases.• Mt. St. Helens

6

Concept Test

• For which terrestrial planets is the main atmospheric gas one of the two main gases produced by outgassing?a. Only Moon & Mercuryb. All five planetsc. Only Venus, Earth and Marsd. Only Earthe. Only Venus and Mars

6

The Terrestrial PlanetsWorld Atmos.

Compsn.Surface Pressure

Ave Surface Temp.

Winds, Weather

Clouds, Hazes

Mercury He, Na, O 10-14 bar Day: 800FNight: -280F

none none

Venus 96% CO23.5% N2

90 bars 880F Slow winds, acid rain

Sulfuric acid clouds

Earth 77% N221% O2H2O

1 bar 60F Winds, hurricanes, rain, snow

H2O clouds, pollution

Moon He, Na, Ar 10-14 bar Day:260FNight: -280F

none none

Mars 95% CO22.7% N2

0.007bar -60F Winds, dust storm

H2O and CO2 clouds, dust

6

Goldilocks Planet

• Delicate balance: Earth is just right.– No oceans without

greenhouse gasses.– Without oceans too

many greenhouse gasses.

– Without oceans no life.

– Without life, no ozone.

– No ozone, no life.• How does Earth

maintain this balance?

6

Carbon Cycle

Tectonics are crucial!

6

Nature’s Thermostat

• Carbon Cycle has negative feedback.• Increasing temperatures lead to

feedback that decreases temperatures, etc.

• Positive and negative feedbacks have nothing to do with desirability of outcome.

6

Too Cool

Less Rain

Less CO2 dissolves in oceans.

More CO2 builds up in atmosphere

Increased greenhouse

Heats Up.

6

Too Warm

More Rain

More CO2 dissolves in oceans.

Less CO2 builds up in atmosphere

Decreased greenhouse

Cool Down.

6

Cycles

6

Human Input

• Affecting CO2 cycle.

• Moving C from ground to air at increased rate.

• No increase in rate of C from air to ground.

6

Mars Today

6

Positive Feedback• Fossil Fuels – Increase CO2 to

atmosphere.• Deforestation – decrease CO2 from

atmosphere• Increase CO2 – Increase greenhouse

effect• Increase temp – Melting glaciers, ice

sheets, polar caps• Less ice – lower planetary albedo• Lower albedo – Earth absorbs more

light• More absorption – Increasing surface

temperatures.

6

Homework #6

• Due Monday January 30:• Read Bennett Chapter 6.• Do: Chapter 6 Quiz