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13B_Mars - GEL36 SOLAR SYSTEM(Ch 22 Lecture 13B Mars...

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1 GEL36 SOLAR SYSTEM (Ch. 22) Lecture 13B: “Mars: Surface Topography, Geology Total topographic relief on Mars is about 30 km (for comparison, the highest peaks to lowest ocean trenches on Earth is about 20 km) - so between Venus, Earth & Mars: Venus is the ‘smoothest’ with the lowest amount of topographic relief (likely due to catastrophic volcanic repaving), Earth is more rugged than Venus, but Mars (even though the smallest planet of the three) has the highest amount of relief - relief on Mars extends from the highest point on the Olympus Mons volcano to the lowest point in the Hellas impact basin Northern hemisphere very different from southern hemisphere. Mars is slightly pear- shaped. Southern hemisphere is mostly old highland cratered terrain - crater counts suggest an age of >3.5 billion years. Averages about 4 km higher elevation than younger volcanic plains to north. Very similar to cratered highlands of the Moon and Mercury. Northern hemisphere is younger lowland volcanic plains . Fewer craters suggest an average age of about 1 billion years, with smaller areas of more recent lava flows (maybe a few hundred million years old - based on crater counts in the youngest lava flows on Olympus Mons). - some evidence suggests that the northern lowlands were once filled with a liquid water ocean, but this remains speculative The difference in elevation between the hemispheres results in a prevailing slope from south to north that was the major influence on the global-scale flow of water early in Martian history. - "it remains to be proven that Mars ever had enough water to fill such a basin. No one has as yet detected any beach features indicating the edges of an ocean." (although it’s possible that micrometeorite erosion may have erased all shoreline features over 3+ b.y.) - hypotheses about the origin of the northern lowlands center on 1) a giant impact early in Martian history, with much of the crust being blasted away as ejecta. Billions of years of smaller impacts, as well as volcanism and sedimentation, have modified the impact crater to a virtually unrecognizable form. 2) Internal processes involving convection currents in the mantle that differentially affected crustal thickness.
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2 Impact cratering Three huge impact basins: Hellas, Argyre, and Isidis, all filled with younger mare-like lava flows and rimmed by basin ejecta. Hellas basin - impact crater 2000 km across 9 km deep filled with mare-type lavas. (Mt. Everest would fit inside) - bigger than Imbrium basin on moon and Caloris basin on Mercury (each about 1500 km across). On Earth, would stretch from East Coast to Rockies and the ejecta would be 2 miles thick and cover the entire U.S.
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13B_Mars - GEL36 SOLAR SYSTEM(Ch 22 Lecture 13B Mars...

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