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9.3-Geology of Moon and Mercury, 9.4-Geology of Mars

Astronomy & Astrophysics
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9.3 Geology of the Moon and Mercury
Geology of the Moon
-maria is dark and smoother, lunar highlands are brighter and heavily cratered
-maria is the only noticeable volcanic features on the Moon
-flat surfaces of maria Æ lunar lava spread easily and far Æ traced back to Moon·s formation
-no water or other gases are a part of the Moon because the giant impact released it and Moon was
formed from the giant impact debris
-few tectonic features found on the maria
-surface wrinkles Æ small-scale tectonic stresses
-the side we don·t see has higher altitude than the near side
-allowed lava to well up and fill crater basins only on the near side
-has very few marias on this side
Moon today
-desolate and nearly unchanging
-geologically dead since maria formed more than 3 billion years ago
-tiny particles burn up and rain directly onto the surface of Moon
-the micrometeorites gradually pulverize the surface rock Æ why the lunar surface is covered by a
thin layer of powdery soil
Geology of Mercury
-impact craters visible everywhere on Mercury
-less crowded together Æ molten lava covered some up during the heavy bombardment)
-these lava flows probably occurred when heat from radioactive decay accumulated to melt part of
the mantle
-Caloris Basin Æ largest single surface feature, huge impact crater Æ more than 1/2 of radius
-has tremendous cliffs Æ past tectonics quite different from other terrestrials
-tectonic forces compressed the crust Æ surface crumple
= did not stay the same size, SHRANK
-shrinking of mercury?
-heat swelled up Mercury Æ cooled Æ contracted by perhaps as much as 20 km in radius
-mantle and lithosphere contracted along with the core Æ tectonic stress Æ great cliffs
-probably closed off remaining volcanic vents, ending Mercury·s volcanisms
9.4 Geology of Mars
-southern hemisphere: Æ high elevation Æ numerous large impact craters (Hellas Basin)
-northern hemisphere: Æ below the average surface level Æfew impact craters
-volcanism was most important in erasing Mars, erosion and tectonics also played a part
-tallest volcano in the solar system (Olympus Mons, large enough to cover Arizona)
-most of the volcanoes are near the Tharsis Bulge
-volcanoes can still be active in Mars
-radiometric dating of meteorites shows some of them to be made of volcanic rock as little as 180
million years ago (very recent)
-Valles Marineris Æ long, deep system of valleys (tectonic feature)
-may have formed tectonic stress accompanying the uplift of material that created the Tharsis Bulge,
cracking the surface and leaving the tall cliff walls of the valleys
-no liquid water exists today Æ unstable on Mars Æ too cold
-mars probably once had very different surface conditions
-warmer temperature, greater air pressure Æ water to flow and rain to fall
-had lots of water at one point
-proved by two twin robotic rovers Spirit and Opportunity
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