16. Planetary Processes

Geologic Processes

Geological Processes• Tectonics

– Rocks bend and break (folding and faulting).• Volcanism

– Materials melt, explode and freeze.• Erosion and surface processes

– Surfaces flatten out: mountains crumble and holes are filled in.§ Mass wasting (gravity action)§ Wind action§ Water action

• Impact Cratering (external)– Bodies from space hit the ground, making a hole.

Tectonics -Folding• When rocks are squashed they will compress

and bend away from the direction of maximum pressure

Wrinkle Ridges on the Moon

• Cooling rocks contract, the shrinkage causes folding and ridges form

Tectonics -Faulting1. Extension Faults -crust moves apart, makes a larger area.

1. Compression Faults -crust moves together, makes smaller area.

1. Strike-slip Faults -crust moves sideways, no gain or loss of area

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What is true of convection that stresses a planet's crust?

A. Mountains may form where the crust is pushed together.

B. Cracks and valleys may form where the crust is pulled apart.

C. Convection has no effect on a planet's crust.

D. A and B

Volcanism

• Materials melt, erupt and explode, then freeze and coat the surface

Generic Volcano Structure

Volcanic Processes• Rocks melt and explode.• 2 components: lava, gasses• Lavas - variable viscosity,depending on chemistry

• Low viscosity range of viscosity High viscosity (runny lava) (gooey, sticky lava)

Low gas content High gas Result: Result: Low broad shapes range of volcanoes Tall cone shapes Volcanic Shield Cinder Stratovolcanoes

Floods Volcanoes cones

Volcanic Floods -VERY low Viscosity

Hawaiian Effusive eruption

Shield Volcano

Olympus Mons Martian Shield Volcano

• Note the broad shield shape and the central cauldera

Volcanic Processes• Rocks melt and explode.• 2 components: lava, gasses• Lavas - variable viscosity,depending on chemistry

• Low viscosity range of viscosity High viscosity (runny lava) (gooey, sticky lava)

Low gas content High gas Result: Result: Low broad shapes range of volcanoes Tall cone shapes Volcanic Shield Cinder Stratovolcanoes

Floods Volcanoes cones

Explosive Stratovolcanos

• Occur only on Eartha product of plate tectonics

Soufrière Hills, Monserrat 1995 Southern half of island evacuated and capital city lost

Alternative Materials

sulfur volcanoes, Io

carbonatites, East Africa, Earth

Water eruption plume, Enceladus

Erosion and Surface Processes Gravity pulls everything into a smooth sphere. Thus,

surfaces flatten out: mountains crumble and holes are filled in.

The processes that carry out erosion each show characteristic patterns that we can see on Earth and on different worlds:

§ Mass wasting (gravity action)- land slides

§ Wind action- sand dunes, wind streaks

§ Liquid action- river channels, ocean shores, glacial erosion

Sand Dunes in the Sahara (imaged by the Space Shuttle)

Ice/tar dunes on Titan

Water Channels on Mars

Ethane Channels on Titan

Impact Cratering• Bodies from space hit the ground, making a hole.

(the only external process -it comes to the planet from the outside)

• The size of the hole depends on the energy of the impact. – A small, slow-moving, ice-ball makes a small hole.– A massive, fast moving, rock makes a large hole.

Imbrium BasinMoon

Crater Dating• Solar System debris falls onto planets at a regular

rate, making craters.• The number of holes on a surface is a measure of

how long it has been exposed to impacts.• Impact craters can be destroyed by the three

internal processes (tectonics, volcanism, erosion)

• Surfaces with few craters have active processes destroying the craters. (called YOUNG surfaces)

• Surfaces with lots of craters have no active processes & are undisturbed. (OLD surfaces)

Which Surface is Older?

A

B

Which World is More Active?(Be able to explain your choice)

Earth Moon

Planetary Atmospheres

Atmospheric Basics

• Our goals for learning• What is an atmosphere?

• How do you obtain an atmosphere?

What is an atmosphere?

An atmosphere is a layer of gas that surrounds a world

How do you obtain an atmosphere?– Gain volatiles by comet impacts

– outgassing during differentiation

– Ongoing outgassing by volcanoes

Keeping an Atmosphere• Atmosphere is kept by the world’s gravity and

temperatures– Low mass (small) worlds = low gravity = little atm.– High mass(large) worlds = high gravity = thick atm.– Low temperatures = slow gases = more atm.– High temperatures =excited gases = atm.loss

• Gravity and pressure– Air pressure depends on how much weight of

gas is there ie. The atmospheric thickness.

What have we learned?• What is an atmosphere?

– A layer of gas that surrounds a world

• How do you obtain an atmosphere?– comet impacts plus outgassing by differentiation,

or volcanoes.– How much atmosphere is retained depends on

the world’s gravity and temperatures

Atmospheric Processes 1

• Our goals for learning

• What are the key processes?

• What creates wind and weather?

• How does the greenhouse effect warm a planet?

Atmospheric Processes

• Atmospheric circulation (convection)– Convection cells move gas from equator to pole and

back. • Coriolis Effect

– Gas dragged sideways by the rotation rate of the world.

• Greenhouse Effect– Infrared energy is re-reflected back to the ground by

CO2

Air MovementGas molecules move from high density to lower density

Atmospheric Pressure

Gas pressure depends on both density and temperature.

Adding air molecules increases the pressure in a balloon.

Heating the air also increases the pressure.(molecules more energetic)

Atmospheric Circulation (convection)

• Heated air rises at equator

• Cooler air descends at poles

Maximum Sun warming

Coriolis Effect

Coriolis Effect breaks upGlobal Circulation

• On Earth the large circulation cell breaks up into 3 smaller ones, moving diagonally

• Other worlds have more or fewer circulation cells depending on their rotation rate

Coriolis Effect

Winds blow N or S Winds blow W or EWinds are diagonal

Venus EarthMars

Jupiter, Saturn Neptune, Uranus(?)

Greenhouse Effect

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If there was no greenhouse effect, Earth...

A. would be warmer than it is today.

B. would have a thicker atmosphere.

C. would be colder than freezing.

D. would have no protection from ultraviolet radiation.

What have we learned?• What creates wind and weather?

– Atmospheric heating and Coriolis effect.

– Solar warming creates convection cells.– The coriolis effect drags winds sideways and breaks up

the cells– The faster a planet spins, the more E-W gas movement

there is• How does the greenhouse effect warm a planet?

– Atmospheric molecules allow visible sunlight to warm a planet’s surface but absorb infrared photons, trapping the heat.