Inner Planetary Geology II. Geology of the Moon The Moon is geologically dead. Cooled so that mantle convection has stopped.

AST 111 LECTURE 17

Inner Planetary Geology II

Geology of the Moon The Moon is

geologically dead.

Cooled so that mantle convection has stopped

Geology of the Moon The Moon is

covered in regolith

A loose, powdery substance – why?

Where did it come from? 4.5 billion years ago,

Earth suffered a massive collision

Ejected material formed the Moon

Composition of moon rocks similar to those found on Earth

Moon has small iron core

Geology of the Moon Two regions

Maria○ Dark, smooth areas

Highlands○ Bright, heavily

cratered

Geology of the Moon

Impact cratering most important geological process on the MoonNo recent volcanism or tectonics to erase

themNo atmosphere to shield from them

Gravity too weak to hold onto an atmosphereNo erosion (requires wind, flowing liquid,

etc.)

Geology of the Moon

A “spike” in impacts happened 700 million years after the Moon formed

Late Heavy Bombardment

May have been caused by migration of Jupiter and Saturn

Geology of the Moon

Lunar maria have few craters

Formed after heavy bombardment period

Geology of the Moon

Maria were created when massive impacts fractured the lithosphere. Heatbuild-up from radioactive decay caused lava to flow up through cracks inthe lithosphere, which flooded the impact crater and created volcanic plains.

Geology of the Moon

Maria are dark because of iron-rich rock

They are large. Must have had very runny lava.

Near-side lithosphere is more thinMore maria on the near side

Geology of the Moon

Geology of Mercury Very similar to the

Moon

Geologically dead

Mercury’s craters less crowded than on the MoonMercury is largerGeologically active

after bombardment

Geology of Mercury Mercury has cliffs (2+

miles high, hundreds of miles long)

Mercury is thought to have shrunk

Huge core, small lithosphere Was HOT, cooled off

quickly “Crumpled” the surface Closed volcanic vents

Geology of Mars Larger than the Moon and Mercury

Smaller than Venus and Earth

Geologically “dying”Had volcanismHad tectonicsHad water erosion

Still a few signs of activity

Geology of Mars

Mars is mostly rocks and dust. It’s cold and desolate.

Geology of Mars It’s orange because

the dust contains iron

Iron rusts when exposed to atmosphere

Geology of Mars Northern

Plains: almostno crateringErased by

geological activity?

Ocean?

SouthernPlains: lotsof craters

Geology of Mars Large shield

volcanoes Tharsis Bulge Olympus Mons: largest

volcano in the solar system

Size of Arizona

Not active Mars is small so its

interior has cooled Lithosphere is

thickening

Geology of Mars Has some tectonic

features

Not many compared to Earth

Valles MarinerisCovers 1/5 of Mars’

equator4x as deep as Grand

Canyon

Geology of Mars

Water erosion features are everywhere! Signs of dried up lakes and riverbeds

Geology of Mars

Liquid water would be “unstable” on Mars right nowLow temperature tries to freeze itLow pressure tries to evaporate it

Because erosion features present:There had to be abundant liquidProbably water

○ Other liquids would freeze / evaporate

Geology of Mars

Surface conditions must have been differentWarmerMore atmospheric pressure

Notice the impact craters in the “riverbeds”2-3 billion years since something was

flowing

Geology of Mars

More evidence for water

Erosion of crater rims,lack of small craters

Sculpted patternsin eroded crater

Valleys often connecttwo lake-like bodies

Geology of Mars Even more evidence

for water

2004, Spirit and Opportunity landed on opposite sides of Mars

Opportunity: Meridiani Plains Spectroscopic evidence

of minerals that form in water

Geology of Mars Frozen water

thought to reside in ice caps, soil

If near volcanic heat, could support life

Evidence for small liquid water flows

Geology of Venus

VENUS = HELL!

What are we looking at?

Surface of Venus Thick cloud cover

won’t let us see surface

Radio waves pass through clouds and bounce off the surface

Geology of Venus

Venus is called “Earth’s sister planet”

Similar mass, size, and interior composition

Extremely different above the surfaceThere is an explanation – next week

Conditions On Venus Sulfuric acid clouds

90x atmospheric pressure than Earth

900 oF on the surface

(Reconstructed from radar data)

Soviet Venera Lander (real picture)

Geology of Venus Impact craters are rare

No small craters

Little erosion – craters persist Too hot for ice or liquid

flow Slow rotation (243

days!) and hot everywhere, so little wind

Geology of Venus Steep

StratovolcanoesThick lava

Shield volcanoes

Volcanoes probably active, no observed eruptions

Geology of Venus

Tectonically activeSurface fractured in

regular patterns

Geology of Venus

Active mantle convectionPushes rock and lava

to the surface

This is a “mantle plume” (note tectonic stress)

Geology of Earth

Lithospheres of Mercury, Venus, Mars are each one solid piece

Earth’s lithosphere is fractured into tectonic plates.

Fractured by mantle convection

Weaker lithosphere than other planets?

Geology of Earth

Earth’s features shaped primarily by plate tectonics

Geology of Earth Plates are fractured

pieces of the lithosphereThey “float” on the

solid mantle

Continents were one landmassFossils found on

shores of different continents

Geology of Earth Tectonic plate

boundaries: large things and large forces

Plates can push together Himalayas: India plate

running into Eurasia plate

Plates can pull apart Rift valleys form

Plates can slide They don’t do it gracefully

(earthquakes)