Chapter 13 - Terrestrial Planets

Differentiation

layered from surface to core

Crust

topmost low-density rocky outer layer

Crust Thickness

70km

Mantle

between the crust and core, composed of dense rock

Core

high-density, metallic composition

Old Surfaces vs. Young surfaces

Old surfaces get more crater marks than younger surfaces

Why is there Old and Young Surfaces?

Internal heat - sourced in remnant of planet formation process (accretion) or by differentiation or by internal radioactive decay

What happens if heat is not cooled instantly?

heat flows outward to the surface of the planet, causing number of geological processes such as Motion of plate tectonics

Characteristics of Small Planets

• radiate heat quickly

• cooler interior

• no convection

• no magnetic field

• no tectonics

Characteristics of Large Planets

• trap more heat inside

• hotter interior

• may have convection

• may have magnetic field

• may have tectonics

Earth’s Average Density

5000 kg/m³

Rock Density

3000 kg/m³

Water Density

1000 kg/m³

Metal Density

8000 kg/m³

Crust Density

3300 kg/m³

How does Earth’s core generate magnetic field?

Self-induced dynamo effect - requires convection in liquid layers as well as fast planetary rotation

How did we learn about Earth’s internal structure?

Examinations of earthquakes

Earth’s Layers in km

• Crust 8-40 km

• Mantle 2900 km

• Outer Core 2250 km

• Inner Core 1300 km

3 points about Active Crust

• Motion of crustal plates produces much of the geological activity on Earth

• Continents on Earth’s surface have moved and changed over million of years

• Most geological features on Earth are recent

Earth’s structure similar to

An egg

Most volume of Earth’s interior

• Molten rocks (80% volume. between 2000-6000 Celsius Magma)

• Thin solid shell (20% volume) only on the surface

Plates

pieces of crust, sitting on a fluid inside Earth called magma

Plate Tectonic Theory

large plates moving slowly against each other, causing geological features and activities over million of years

Geological Features

Mountains, volcanoes, valleys, oceans and earthquakes

North American Plate Shift

Shifts 8cm per year

Longest Mountain Range

Mid-Ocean Rise

Terrestrial Atmosphere Composition

• Moon: no atmosphere + -173-177 celsius

• Mercury: no atmosphere + -173-427 celcius

• Venus: lots of CO2 + 9200 pressure + 464 celcius

• Earth: lots of nitrogen + 101 pressure + -90-60 celcius

• Mars: lots of CO2 + less pressure + -143-35 celcius

First (Primary) Atmosphere

earth’s atmosphere was initially rich in CO2, nitrogen and water vapour, as the planet cooled down, CO2 was scrubbed out by oceans, leaving atmosphere rich in other gases like nitrogen

Secondary Atmosphere

the air we breath now

Great Oxidation Event

2/2.5 million years ago, plants in oceans and lands began to rapidly produce oxygen via photosynthesis, oxygen levels began to rise

Ozone

upper atmosphere protects Earth from harmful UV rays

Green House Effect

atmosphere rich in CO2 can trap heat, leads to the increase of surface temperature (global warming)

CFCs (ChloroFluoroCarbons)

produced by human activities, destroy ozone

Kyoto Protocol

operationalizes the UN framework convention on climate change by committing and reduce greenhouse gas (GHG) emissions in accordance with agreed individual targets

Why does the moon have no atmosphere?

• weak surface gravity, low escape velocity

• gas particles heated by radiation from Sun

• speed of gas particles exceeds escape velocity

• gasses drift away into space

Why is there temperature variation from -173 to 117 C?

• high temperature: no atmosphere to transport heat towards cooler locations

• low temperature: no atmosphere to trap heat (radiates quickly back to space)

Maria

lunar lowlands filled by successive flows of dark lava

Albedo

ratio of the amount of light reflected from a surface to the amount of light received by the surface

High albedo

Reflects

Low Albedo

absorbs

Highlands

heavily cratered, lighter-coloured regions, composed of low density rock, older than the maria

Breccia

rock fragments bonded together by heat and pressure

Apollo Mission

helped us learn lunar geology by bringing moon samples

Moon Samples in kg

400 kg

Fine rock/dust on the surface of the Moon

result of pulverization by micro-bombardment over years

3 Hypothesis of the Origin of Earth’s Moon

1. Fission hypothesis - moon broke off from a rapidly spinning proto-Earth

2. Condensation hypothesis - Earth and its Moon condensed from the same cloud of matter in the solar nebula

3. Capture Hypothesis - moon formed elsewhere in the solar nebula and later captured by Earth

Large-impact Hypothesis

suggests that the moon formed when a planetesimal, estimated to have been at least as large as Mars, grazed the proto-Earth

History of Earth’s Moon

• Magma Ocean - moon formed in mostly molten state

• Cratering and basin formation - began as soon as the crust solidified

• Multiringed basin - also formed

• Increased cratering rate occurred during the late heavy bombardment

Formation of Maria

• surface solidified 4.4 billion years ago

• Large impacts created wide deep basins

• Cracked crust down to mantle

• Mantle material seeped through cracks to fill basins

How many people stepped into the moon?

12

What was the fear of initially going to the moon?

transferring a disease and bringing it back to earth

Does Mercury have any natural satellites?

No

Marine 10

Flew past Mercury and revealed a planet heavily cratered

Why does Mercury have no atmosphere?

• weak surface gravity, low escape velocity

• Gas particles heated by radiation

• Speed of gas particles exceeds escape velocity

• Gasses drift into space

• No atmosphere, no wind/rain thus no erosion

Mercury Interior

• Large metallic core

• Formed closer to the sun → mostly metals condensed at the core

• Similar to a cannonball bc its metal core nearly 85% of the volume of the planet

Giant Scarps (Cliffs)

Tectonic motion due to global contraction, Mercury shrank as it cooled and its crust wrinkled to form ridges

Venus’ solid surface

Hidden beneath thick atmospheric clouds

Venus Rotation Direction

Backwards, sun rises west, sun sets east

Venus Revolution

224 Earth Days

Sunrise at Venus

Rise once every 117 Earth days, ruses two times each year

Venus Atmosphere

• very hot, very dense

• 96% CO2 - caused a runaway greenhouse effect in the past

• Rest are acids

• Pressure 90x larger than Earth

Earth Atmospheric Pressure

1 atmosphere (atm)

Surface of Venus

• atmosphere not transparent to visible and infrared, radio waves are used to scan the surface

• volcanoes, faults, and sunken regions produced when magma below the surface drained away

Coronae

large round geological faults in the crust caused by the intrusion of magma below the crust

USSR Lander (Venera13)

survived only few hours on the surface of Venus and sent incredible pictures

Mar’s Solar Day

24.66 hours (similar to Earth)

Mars Rotational Axis

25.2 (similar to Earth)

Seasons at Mars

distinct seasons similar to Earth, twice as long

Mars distance to sun

1.5 AU

Mars Orbital Period around the sun

687 Earth Days

Mars Atmospheric Pressure

0.01 atm

Permafrost

permanently frozen soil

Mars Atmosphere

• Martian air contains 95% CO2, 3% nitrogen and 2% argon, no ozone, no protection against UV

• only 1% dense as Earth

• surface temperature varies from -150 C to !5C

Mars Odyssey

• 2001

• success

• high resolution images of Mars

Exploration Rover - Spirit

• 2003

• US

• success

• operated for over 6 years on Mars. long past design life

Exploration Rover - Opportunity

• 2003

• US

• success

• Operated for nearly 15 years, reviving record 28 miles (45km)

InSight Lander

• 2018

• US

• success

• measuring “Marsquake” and studying interior

Preservation Rover

• 2020

• US

• success

• searching for signs of ancient life and collecting samples for future return to Earth

Olympus Mons

• largest volcano in Solar System

• 625 km wide, 22 km to summit, surrounded by 6 km high cliffs

Earth has plate tectonic and Mars has…

no motion of the crust, rather magma rises up and forms the tallest volcano

Water in Mars

• once existed in large quantities

• outflow channels and valley networks show evidence of water

• no liquid water, but found frozen water (extending at least kilometer)

Solar Wind Stripping

the solar wind stripped tjje atmosphere away

Mars’ Moons

Phobos and Deimos

Phobos size

• 28×23×20 km

• captured asteriod

Deimos

• 16×12×10 km

• captured asteroid

History of Mars

1. differentiation

2. core cooled down quickly, shut off dynamo effect, no magnetic field

3. cratering may have broke, triggering lava flows that flooded occasionally erupt

4. volcanoes may occasionally erupt

5. age of liquid water must have ended more than 3 billion years ago

6. solar wind stripping

7. pressure dropped, temperature dropped. not strong heat convection