Inner Planetary Geology II AST 111 Lecture 17

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 Highlands Dark, smooth areas Bright, heavily cratered

Geology of the Moon Impact cratering most important geological process on the Moon No recent volcanism or tectonics to erase them No atmosphere to shield from them Gravity too weak to hold onto an atmosphere No 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 Gives an estimate of duration of heavy bombardment period.

Geology of the Moon Maria were created when massive impacts fractured the lithosphere. Heat build-up from radioactive decay caused lava to flow up through cracks in the 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 thin More 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 Moon Mercury is larger Geologically 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 volcanism Had tectonics Had 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: almost no cratering Erased by geological activity? Ocean? Southern Plains: lots of craters

Geology of Mars Large shield volcanoes Not active 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 Marineris Covers 1/5 of Mars’ equator 4x 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 now Low temperature tries to freeze it Low pressure tries to evaporate it Because erosion features present: There had to be abundant liquid Probably water Other liquids would freeze / evaporate

Geology of Mars Surface conditions must have been different Warmer More 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 patterns in eroded crater Valleys often connect two 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 surface There is an explanation – next week

Conditions On Venus Sulfuric acid clouds 90x atmospheric pressure than Earth 900 oF on the surface Soviet Venera Lander (real picture) (Reconstructed from radar data)

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 Stratovolcanoes Shield volcanoes Thick lava Shield volcanoes Volcanoes probably active, no observed eruptions

Geology of Venus Tectonically active Surface fractured in regular patterns

Geology of Venus Active mantle convection Pushes 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 lithosphere They “float” on the solid mantle Continents were one landmass Fossils 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)