The Solar System
Terrestrial Planets
Earth
• Average distance from
the Sun: 1.00 AU
• Radius: 6,378 km
• Mass: 5.97 × 1024 kg
• Avg. density: 5.52 g/cm3
• Composition: rocks,
metals
• Average surface
temperature: 290 K
• Satellites: 1
Earth’s Structure
• Core – highest-density
material, mostly Ni & Fe
• Mantle – moderate
density, mostly Si, O, etc.
• Crust – lowest-density
rock, granite & basalt
Structure
Internal Heat
Formation
• Caused by accretion and
collisions during formation
• Also due to radioactive
material
• Differentiation
Geological Activity
• Convection and Cooling
Magnetic Field
• Caused by the motion
of charged particles in
Earth’s molten outer
core
• Magnetosphere
protects us from solar
wind
Shaping Earth’s Surface
• Cratering
• Volcanism
• Tectonics
• Erosion
Earth’s Atmosphere
• 77% N2, 21% O2
• Protection
– X-rays are absorbed high
up in the atmosphere
– Ozone absorbs UV
– Visible light gets through
no problem
Earth’s Atmosphere
Scattering
• Blue light is scattered more
easily than red light
• Sky is blue because sunlight
gets scattered to your eye
from all directions
• Sun look red at sunrise/set
because blue light gets
scattered away
5800 K
Greenhouse Effect
 T  k
Visible Light
300 K
CH4
IR Light
H2O CO2
Ground
Geologically Dead Objects
The Moon
• Average distance from
the Earth: 384,000 km
• Radius: 1,700 km
• Mass: 7.3 × 1022 kg
• Avg. density: 3.35 g/cm3
• Period: 29.5 days
Geological Features
Lunar Maria
Micrometeorites
Mercury
• Average distance from the
Sun: 0.39 AU
• Radius: 2,440 km
= 0.38REarth
• Mass: 0.055 MEarth
• Avg. density: 5.43 g/cm3
• Composition: rocks, metals
• Average surface
temperature: 700 K day, 100
K night
• Satellites: 0
• 88 day orbit, 59 day rotation
Geological Features
One giant crater called “Caloris Basin”
Mars
• Average distance from
the Sun: 1.52 AU
• Radius: 3,397 km
= 0.53REarth
• Mass: 0.11 MEarth
• Avg. density: 3.93 g/cm3
• Composition: rocks,
metals
• Average surface
temperature: 225 K
• Satellites: 2
Mars vs. Earth
Similarities
• Day is about 25 hours long
• Polar caps
• Axis tilted about the same
Differences
• More extreme seasons in
southern hemisphere
• Polar caps contain CO2
• Only about 1% of Earth’s
atmosphere, which is CO2
• Much colder
Perhaps it was more similar long ago
Martian Geology
Martian Geology
• Polar ice caps
• Higher elevation of
southern hemisphere
• Lack of craters in
northern hemisphere
• Tharsis Bulge, Valles
Marineris
Martian Geology
• Olympus Mons
– The largest volcano in
the solar system
– Base covers an area
equal to Arizona
– 26 km above average
surface level, 3x the size
of Mt. Everest
Water on Mars
• Today the surface
temperature and
pressure to too low for
liquid water
• Polar caps
• Ground water
• Evidence of ancient H2O
– Dried Riverbeds
• Maybe not
– Signs of erosion
What happened?
Venus
• Average distance from
the Sun: 0.72 AU
• Radius: 6,51 km
= 0.95REarth
• Mass: 0.82 MEarth
• Avg. density: 5.24 g/cm3
• Composition: rocks,
metals
• Average surface
temperature: 740 K
• Satellites: 0
Venusian Geology
• Craters, volcanoes,
tectonics somewhat
similar to Earth
• Coronae – bulges made
by hot, rising plumes of
mantle
• No plate tectonics
Venusian Atmosphere
• Atmosphere about 90x as thick as Earths
• Made up of about 96% carbon dioxide, but
virtually no water
• Why should the atmosphere be different
from Earth’s?
Why are the atmosphere’s different?
Earth
• Water rained into oceans
• CO2 dissolved into water
and then formed into
carbonate rocks
– Including the rocks, Earth has
about as much carbon dioxide
as Venus
Venus
• Lacking water
– Explains why there is more
carbon dioxide in the
atmosphere: cannot dissolve
and become rock
• Where did the water go?
– UV light breaks up molecule
Runaway Greenhouse Effect
Life
What is necessary?
A few examples
• Liquid Water
• Atmospheric Oxygen
• Climate Stability
• Planetary Size
– Must be large enough so
it doesn’t cool too
quickly, preventing
tectonics
• Distance from Sun
– Liquid Water
The CO2 Cycle
Global Climate Change
Global Climate Change