Terrestrial Worlds 1

Mercury

Mercury

• 1974 -Mariner 10 flyby

• 2008-Current -MESSENGER

Mercury’s Surface

What is the most common process

on mercury?

Mercury’s Surface

• A mixture of heavily cratered and smooth regions like the Moon

• Smoother regions are likely ancient lava flows

Caloris basin

Multi-ring impact basin

(Only half visible from Mariner 10)

Caloris basin MESSENGER 2009 -1550km

Volcanism on Mercury

• ancient lava flows, no large floods

Tectonics on Mercury

Cooling causes shrinkage causing fault scarps (cliffs)

Mercury Atmosphere

MercuryMercury

–10-14 bars of pressure (negligible)• Gas comes from impacts that eject surface atoms

–Temperatures: 800 oF in day (second hottest) -300 oF at night

Terrestrial Worlds 2

Venus,

Venus basics• 2nd planet from Sun (0.7 AU), 6th largest world.• Orbit -224 Earth days• Sidereal rotation -243 Earth days (solar day-117 Eds)• Surface gravity-8.8 m/s2 (90% of Earth)• Intense cloud cover - highly reflective in visible light,

surface unseen except by radar• Spacecraft- Pioneer, Magellan (USA) Venera 9-16 (Russia)

Highlands on Venus- Aphrodite Terra

Venus - Chasma

Vast mountain and canyon systems.

-3km high and 3km deep running for thousands of miles

Venus- Regios

RegionsWhere canyon

systems join at a

high volcano

Tectonics• Downwelling -Highlands and faulted

regions called tessera

• Upwelling-Extension rifts at hot spots= chasmas and regios

Crust too strong to break all the way through. No plate tectonics

Volcanism on Venus

• 80% of Venus is resurfaced by volcanism

• Volcanic shapes controlled by height and location.

• Hot spots -large shield volcanoes.

• Lowlands - volcanic floods.

• Middling heights- fields of cinder cones.

• High areas - lava too hard to rise - coronae

Venus Surface Processes - WindWind streak showing wind direction

Venus Cratering

• Lots of small to middle-sized craters, few large ones

• Even distribution -Most of Venus’ surface has a similar age

• Most of Venus resurfaced by catastrophic lava flooding < 1 billion yrs ago.

• Current activity??

Venus Atmosphere

• 90 bars of pressure (90 x Earth)

• 96% CO2 3.5% N2 < 1% others

• Massive greenhouse warming.– Venus is the hottest planet. 870 oF

• Clouds- sulfuric acid!

• Slow rotation - almost no coriolis effect.

Terrestrial Worlds 3

Earth - The most unique of all

Earth basics

• 3rd planet from Sun (1 AU), 5th largest world• Orbit - 1 Earth year• Sidereal rotation - 23.9 hours (solar day -24 hrs)• Surface gravity- 9.8 m/s2.• 1 bar of pressure

• 78% N2 21% O2 < 1% others 0.003 CO2.

• Temperatures- ~100oF summer (max. 140oF, deserts)

- ~0 oF winter (min. -130 oF, poles)

Unique Features

• oceans,

• Plate tectonics

• oxygen atm.

• Life!

EarthquakesDetected earthquakes form lines

Earth’s crust broken into pieces~8 large and 10 small plates

Crust follows Convection Currents• Rising current (hot)

• Plate dragged aside

• Breaks at weakest point (where it is hottest)

• New lava wells into gap.– DIVERGENT boundary

• Falling current drags plate after it.

• 1 plate hits another and sinks.– CONVERGENT boundary

Earth -tectonics

• All a consequence of internal convection:

– Extension faults occur at upwelling of mid-ocean ridges (divergent boundary)

– Compression faults occur at downwelling of subduction zones (convergent boundary)

– Strike-slip faults occur as plates jostle around,

Earth -Volcanism

• All a consequence of internal convection:

– Low viscosity lavas occur at upwelling of mid-ocean ridges -shield volcanoes

– High viscosity lavas occur at subduction zones as crust is remelted - tall, explosive, stratovolcanoes

Result: Earth is the ONLY world to have stratovolcanoes, because it’s the only world to have plate tectonics

Lava erupted at the mid ocean ridge

Stratovolcano on continent side of subduction zone

Earth - Erosion & Surface processes

• Mass wasting

• Wind -deserts

• Biological (unique)

• Water -main process River Channels erode at head, deposit at mouth Materials move along beaches Glaciers grind material down

Earth has about 200 craters at the surface.

Earth -Cratering

Earth’s Volatiles(atmosphere and hydrosphere)

Earth is unique in that:

• the majority of it’s volatiles are liquid.

• Atmospheric composition is not all CO2 (78% N2 , 21% O2 ,<1% others, 0.003 CO2 )

• Life affects the atmospheric balance.

Earth Oceans and TemperatureWhy does Earth have oceans

while Venus and Mars do not?• Earth is the right temperature to have liquid

water due to distance from the Sun.

• Temperatures are maintained by moderate greenhouse warming

• CO2 balance maintained by oceans and life

– (they act as a sink for all the CO2 that would otherwise be in the atm. making extra warming)

• Magnetic field prevents H2O breakup.

Why Does Earth have a Nitrogen/Oxygen Atmosphere?

• Most of the CO2 is locked up. Nitrogen is the main ingredient left.

• Plant life produces oxygen, as plants increase oxygen levels increase. Large excess over time.

• Some of excess oxygen gets broken and remade into ozone

– (3 O2 molecules become 2 O3)

Terrestrial Worlds 4

Our Moon

Moon basics

• Earth’s nearest neighbor , 14th largest world

• Orbit -27.3 Earth days

• Sidereal day -27.3 Earth days

• Surface gravity -1.61 m/s2 (16% of Earth)

• No global magnetic field

• Only world visited by humans

Near Side Far Side

Compare and contrast the 2 sides of the Moon

Maria make up 16% of the Moon’s surface and almost all of them are on the Near side

Main lunar materials

• White highlands – Anorthosite (a rock full of white feldspar)

• Dark maria– Basalt (black from iron content)

Volcanism – Maria Formation• fluid basalts make flood plains that fill large craters • All occur early in lunar history, 3.8-3.2 billion yrs ago

Large impact crater weakens crust

Heat build-up allows lava to well up to surface

Cooled lava is smoother and darker than surroundings

Impact cratering is dominant

process

Surface Processes• Mass Wasting

• Radiation damage

Moon vs. Mercury

What do you think is similar about them? What is different?

• What processes shaped our Moon?– Early cratering still present– Maria resulted from early volcanic floods– no shrinkage scarps

• What processes shaped Mercury?– Cratering similar to Moon, – some volcanism, but no large floods– Shrinkage scarps

Moon Formation

• Early Theories: Capture, Co-formation(twin), broken off from Earth (fission).

• Chemistry of Moon rocks show Moon is both like and unlike Earth

• Result: Impactor Theory– Moon formed by a giant asteroid striking a

glancing blow on the Earth

Impactor Theory

Giant impact stripped matter from Earth’s crust

Stripped matter began to orbit

Then accreted into Moon

Lunar Atmosphere

–Temperatures 225 oF in day

-243oF at night

MoonMoon

–10-14 bars of pressure (negligible)• Gas comes from impacts that eject surface atoms

Why are smaller terrestrial bodies such as Mercury or the

Moon "geologically dead"?

A. They don't have volcanoes.

B. They cooled off faster than Earth did.

C. They don't have erosion.

D. They were hit by fewer meteorites than Earth.

Terrestrial Worlds 5

Mars

Mars basics• 4th planet from Sun (1.5 AU), 7th largest world• Orbit - 1.88 Earth years• Sidereal rotation - 25 hours• Surface gravity- 3.71 m/s2 (39% of Earth)

• Too cold for liquid water (only ice or gas)• Spacecraft- Russian program mostly unsuccessful - USA- Vikings 1& 2 in 1970s - “Follow the Water” program 1990s-now

Map of Mars

Mars Polar Caps -Solid CO2

North South

Color height map of Mars(Red-high, Blue-low)

Mars- Volcanism

• Two main types of Volcanism:

• Older- fluid lavas, flood plains and flattish volcanoes (forms the older surfaces on Mars)

• Younger- large shield volcanoes

(Tharsis region and Elysium region).– Note. The volcanoes pour out as much lava as the

Hawaiian islands, but without plate tectonics it piles up in 1 place, making giant volcanoes.

Tharsis Bulge Volcanic region

Olympus Mons

Largest Volcano in the Solar System

Mars tectonics -Tharsis extension faulting

Tharsis extension faultingNoctis Labyrinthusand Valles Marineris

3000 miles long, 7 miles deep

Valles Marineris

Mars Cratering

• Surfaces old in southern highlands

• ‘Middle aged’ in the Northern lowlands

• Largest craters are in south, from age of Heavy Bombardment:– Argyre basin ~1120 miles across– Hellas ~1430 miles across

Mars Cratering - Hellas basin

Mars Cratering

- Hellas is over 9km deep

Mars Surface Processes -(Dominant)

1) Wind

Fields of sand dunes

Mars Surface Processes – 2) Water

Water channels seen across the surface

Mars Surface Processes – 2) Water

Water channels seen across the surface

Opportunity at Sinus Meridiani - A dried up lake?

Evidence of Running Water at Sinus Meridiani

• Jarosite a mineral made in water.

• High sulfur & chlorine levels- salt pan from dried lake.

• Vugs -holes left after water dissolves away minerals.

• “Blueberries” -spheres of hematite made in water.

• Cross-bedding -rock forms made from water ripples.

The Missing Water -Underground Ice?

The Martian Atmosphere

• 0.007 bars of pressure (1/100 x Earth)

• 96% CO2 3.5% N2 < 1% others

• Temperatures-

13 oF in day (max. recorded 63 oF)

-135 oF at night (min. -200 oF at poles)

• Current pressure/temperature conditions are too low for stable liquid water. Water found as gas or ice.

• Mars has not had widespread surface water for 3 billion years

• Greenhouse effect probably kept surface warmer before that

• Somehow Mars lost most of its atmosphere

Climate Change on Mars

• Traces of magnetic field only found on oldest rocks.• Younger rocks no field.• Mars once had magnetic field early on, but not today.

• Magnetic field may have protected early Martian atmosphere from the solar wind.

• Solar wind may have stripped atmosphere away after field decreased because of interior cooling.

• If much water and carbon dioxide was lost, the Martian greenhouse effect would decrease and the temperatures would be too low for liquid water.