Michael Redmond Notes

Chapter 7

Earth and the Terrestrial Planets

Mercury

•
•
•

Craters
Smooth plains
Cliffs

Venus

•
•

Volcanoes
Few Craters

Mars

•
•
•

Some Craters
Volcanoes
Riverbeds

Moon

•
•

Craters
Smooth plains

Earth

•
•
•
•

Volcanoes
Craters
Mountains
Riverbeds

SECTION 7.1

Earth as a planet

Earth’s interior

•
•
•

Core: highest density; Nickel, Iron
Mantle: Moderate density; Silicon
Crust: Lowest density

Differentiation

•
•

Lithosphere

•
•

A planet’s outer layer of cool, rigid rock is called the lithosphere
It floats on the warmer, softer, rock underneath

Strength of Rock

•

Rock stretches when pulled slowly but breaks when pulled rapidly

Convection: Hot rock rises and cool rock falls. One convection cycle takes 100 million years on earth.

Sources of internal heat

•
•
•

Gravitational potential energy of accreting planetesimals
Differentiation
Radioactivity

Heating of interior over time

•
•

Accretion and differentiation when planets were young
Radioactive decay is most important heat source today

Cooling of interior over time

•

Convection

Surface area to volume ratio

•
•
•

Heat content depends on volume
Loss of heat through radiation depends on surface area
Larger objects have a smaller ratio and cool slower

Earth’s Magnetosphere

•
•

Protects us from charged particles from the Sun
The charged particles can create aurorae

How do we know?

•
•
•
•

P Waves, push matter back and forth
S Waves, shake matter side to side
P Waves go through the Earth’s core but S Waves do not
We conclude that earth’s core must have a liquid outer layer

Geological Processes

Gravity pulls high density material to the center of the Earth.
Lower density rises to the surface

•
•
•
•

Impact cratering – asteroids or comets
Volcanism – Eruption of molten rock to the surface
Tectonics –
Erosion

Impact Cratering

•
•

Most cratering happened soon after the solar system formed
Craters are about 10 times larger than the meteor.

Volcanism

•
•

When molten rock (magma) finds a path through the lithosphere to the surface
Molten rock is called lava after it reaches the surface

Tectonics

•
•

Convection of mantle creates stresses in the crust called tectonic forces
Compression forces make mountain ranges

Erosion

•

Weather – driven process that break down or transport rock

Processes that cause erosion

•
•
•

Glaciers
Rivers
Wind

Earth atmosphere affect the planet

•
•
•
•

Erosion
Radiation protection
Greenhouse
Makes sky blue

Radiation Protection

•
•

All X-Ray light is absorbed very high in the atmosphere
Ultraviolet is absorbed by the Ozone (O3)

Greenhouse Effect

•

Keeps earth warm by trapping heat with carbon in the atmosphere

•
•

Let sunlight through but trap from escaping
Keeps water liquid

Greenhouse Gas

•
•

Why is the sky blue?

•
•

Atmosphere scatters blue light more
Sunset is red because the more atmosphere the light goes through blue light is already scattered
and red gets to you

SECTION 7.2

The moon and Mercury: Dead

Moon

•
•

Some volcanic activity 3 billion years ago must have flowed. Flooded craters
Lunar Maria

Mercury

•

Craters are more spread apart

Tectonics of Mercury

Any gas that absorbs infrared
(CO2), (H2O),(CH4)

•

Long cliff indicate Mercury shrank early in its history

Mars vs. Earth

•
•
•
•
•

50% Earth radius , 10% Earth mass
Axis tilt about the same as Earth
Similar rotation period
Thin CO2 atmosphere: little greenhouse
Dry Ice (CO2) poles

Seasons

•
•

More extreme on the south because of the more elliptical orbit
Seasonal winds create huge dust storms

Water?

•
•
•
•

Why did Mars change?

•
•
•
•

Venus

• Impact Craters, but fewer than other planets
• Volcanoes, many
• Tectonic stress, canyons
• Little erosion
ü Doesn’t appear to have plate tectonics

Why so hot?

•
•
•

Venus Atmosphere

•
•

Runaway Greenhouse Effect

•
•

Shows ancient riverbeds
Ice
Volcanoes 180 million years ago
2004 a rover found evidence of a liquid flowed on Mars

Size
Greenhouse effect
Magnetic field protected early Maritain atmosphere
Interior cooling because Mars is small

Greenhouse effect keeps its surface
Thick carbon dioxide atmosphere
Earth escapes this fate because carbon is in mostly rocks

Reflective clouds contain droplets of sulfuric acid
The upper atmosphere has fast winds that remain unexplained

Greater heat more evaporation, more evaporation faster greenhouse effect
No plate tectonics / No carbon cycle

SECTION 7.5

Earth as a Living Planet

Why unique features of Earth are important for life?

• Surface liquid water
• Atmospheric oxygen
• Plate tectonics
• Climate stability
ü Earths distance from the Sun make the greenhouse effect moderate so liquid water is possible
ü Photosynthesis makes oxygen
ü Plate tectonics is an important step in the carbon cycle

Continental Motion

•
•

Can be measured with a GPS
Seafloor is recycled through a process known as subduction
Ø One plate goes below the other

Carbon dioxide cycle

•
•
•
•

Long term climate change

•
•
•

What makes a planet habitable?

•
•

Atmospheric CO2 dissolves in rain water
Rain erodes minerals that flow into the ocean
Minerals combine with carbon to make rocks on the ocean floor
Volcanoes put CO2 back

Changes in the axis tilt might lead to ice age
Wide ice tends to lower global temperature by increasing Earths reflectivity
CO2 from outgassing will build up greenhouse effect to warm again

Located at an optimal distance from the Sun for liquid water to exist
Large enough to be geologically active

Chapter 8

Jovian Planets

What are Jovian planets made of?

Jupiter and Saturn

•
•

Uranus and Neptune

•
•

Jovian planet formation

•
•
•

•

Interior of Jovian Planets

•
•
•
•

Inside Jupiter

•
•
•
•
•

Jupiter’s atmosphere

•
•
•

Mostly H, He gasses
Jupiter and Saturn H, He / Neptune, Uranus H compounds

Mostly H compounds: H2O, CH4, NH3
Some H, He and rock

Beyond the frost line, planetesimals could accumulate ice
Cores are very similar
Planets formed early captures the most H, He gasses. Solar winds stop the accumulation of
gas
Forms in a denser part of the nebula forms first

No solid surface
Layers under high pressure and temperature
Core made of Hydrogen compounds
The layers are different for different planets

High pressure inside of Jupiter causes the phase of H to change with depth
H acts like a metal at great depths
The core is thought to be mad of rock metals and H compounds
Models suggest that cores of Jovian planets have similar composition
Neptune and Uranus have no metallic H so no magnetic field

H compounds in Jupiter condense to form clouds
Different cloud layers correspond to the freezing temp of compounds
Ammonium sulfide clouds (NH4, SH) reflect red/brown

Saturn

•

Layers are deeper in

Neptune and Uranus

•

Methane gas reflects blue light

ü All Jovian planets have strong winds and storms

Section 8.2

Moons of Jovian Planets

Medium and large Moons

•
•
•

Small moons

•
•

Enough self gravity to be a sphere
Have substantial amounts of ice
Circular orbits in the same direction of the planet rotation

Far more numerous
Not enough gravity to be spherical

ü IO is the most volcanically active body in the solar system

Europa’s Ocean: Waterworld?

•
•

Ganymede

•
•

Callisto

•
•

Tidal stresses crack Europa’s surface ice
Interior also warmed by tidal heating

Largest moon in the solar system
Clear evidence of geologic activity

Cratered ice ball
No tidal heating

Titan

•
•
•
•

Medium moons of Saturn

•

Medium moons of Uranus

•

Neptune’s Moon Triton

•
•

Rocky Planets vs. Icy Moons

•
•

Saturn’s Rings

•
•
•
•

Why do the Jovian Planets have rings

•
•
•
•
•

Only moon with a thick atmosphere
Mostly nitrogen, argon, methane, ethane
Liquid methane, “rocks” made of ice
Titan’s surface revealed dark, smooth regions that maybe lakes of liquid methane

Almost all show evidence of past Volcanism

Varying amounts of geologic activity

Similar to Pluto but larger
Evidence of past geological activity

Rock melts at higher temp
Only large rocky planets have enough heat for activity

Made up of numerous, tiny individual particles
Orbit Saturn’s equator
Some small moons create gaps within rings
Very thin

All Jovian planets have rings
Form from dust from impacts on moons orbiting those planets
Because they have small moons close-in
Impacts are random
Saturn’s rings may be an accident

Chapter 9