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

Greenhouse Effect

Ground

Visible Light IR L

ight

H2O CO2 CH4

300 K

kT

5800 K

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