inner planetary geology ii. geology of the moon the moon is geologically dead. cooled so that...
TRANSCRIPT
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!
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)