Lecture 23

Movie Night 2 Monday, April 19 SW119 from 7:00~9:30

How do surface building processes apply to the Terrestrial Planets? Vulcanism Impact cratering Erosion Tectonics

erosion cratering vulcanism tectonics

Small rocky planets Cold, solid interiors (Moon, Mercury)‏ Tectonic & volcanic activity only during first billion years Many ancient craters Little outgassing Atmospheres lost due to weak gravity No erosion (Moon, Mercury)‏

Mercury Geologically dead Vulcanism when young (small lava plains, smaller crater density than lunar highlands)‏ Days / Nights last 3 months – very hot / cold

Mercury Tectonics when young Very high cliffs extending for hundreds of kilometers, formed as folds as planet cooled and contracted

Moon Highlands (light colored areas): heavily cratered about four billion years old

giant impact basins flooded with lava Mare Dark colored areas: giant impact basins flooded with lava lightly cratered about 3.2-3.9 billion years old (younger than highlands)‏

(Earth, Venus)‏ Large rocky planets Warm, convecting interiors Ongoing tectonic & volcanic activity Most ancient craters erased Considerable outgassing Atmospheres retained Erosion exists

Venus Fully cloud covered – surface not visible

Surface features on Venus have been investigated using radar from orbiting spacecraft

young surface mostly gentle rolling plains.

evidence of volcanism.

Erosion & tectonics

few impact craters

tectonic activity (folded grooves shown here)

Mars Marsrovers.jpl.nasa.gov

erosion cratering vulcanism tectonics

heavily cratered southern hemisphere fewer craters in northern hemisphere heavily cratered southern hemisphere

giant volcanoes

Covers area the size of Arizona Olympus Mons Covers area the size of Arizona

dry stream beds, once had running water

Considerable evidence of water flows – younger terrain

heavily cratered southern hemisphere Older terrain

Tectonics & erosion

Erosion around edge of Olympus Mons

part of surface young, part old Conclusion: part of surface young, part old

Summary: Surface Properties

Cratered terrain ubiquitous in the solar system cratering due to planetesimals left over from formation of solar system smallest planets (Moon, Mercury) heavily cratered middle sized planet (Mars) has both heavily cratered and also relatively uncratered regions and extinct volcanos largest planets (Venus, Earth) have few craters and active volcanos

Why? More impact craters implies an older surface Rate of cratering declined rapidly after planet formation Many craters remain where there is no tectonic or volcanic activity

Why do some planets have old surfaces and some young surfaces? The level of tectonic and volcanic activity

Thickness of lithosphere controls extent of volcanic activity. Thin lithosphere -> hot rocks from interior break through surface Thick lithosphere -> hot rocks from interior can't break through surface.