final_review

final_review - AST 5: Life in the Universe, Fall 2006, UCLA...

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AST 5: Life in the Universe, Fall 2006, UCLA Final review (Following topics are token out from your textbook. This review doesn’t cover everything in the second half of this class, but just some issues that might be important to go through again) Chapter 7: Mars 7.1 Fantasies of Martian civilization 7.2 A current assessment of the habitability of Mars z Mars today: ± At surface -> freezing, dry, low air pressure (1% of Earth’s), no abundant oxygen for breathing, no ozone, weak gravity (40% of Earth’s) ± Seasoning -> Due to the titled rotation axis (similar to the case of Earth), but the southern hemisphere is hotter in its summer due to closer distance to the Sun. ± The seasons on Mars change the CO 2 content in the Martian atmosphere. About 1/3 of CO 2 of Martian atmosphere cycles seasonally between the north and south polar caps. ± Liquid water is not stable on the Martian surface today. It could either evaporate or freeze right away (because the low air pressure and low temperature). But just in this week, NASA announced the discovery of possible evidence of liquid water on the Mars surface. z The Geography of Mars: ± Northern hemisphere: below the average surface height, very few impact craters. <- Erosion. Younger surface. ± Southern hemisphere: higher, numerous large impact craters, older surface. ± A chain of volcanoes in Tharsis region: a long serious of volcanic eruptions from mantle plume (like the case of Hawaiian islands) ± Geological Eras on Mars: (b.y.a. = billion years ago) ² Noachian: 4.6 – 3.7 b.y.a. – heavy bombardment ² Hesperian: 3.7 – 1.0 b.y.a. – volcanism activity decreased steadily since 3.5 b.y.a. (smaller planet cools faster). ² Amazonian: 1.0 billion years ago to present
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z Evidence of liquid water on Mars ± Riverbeds ² Made by heavy rainfall or underground water flow (sapping). ² Exclusively in heavily cratered terrain – they are old. Mars must be warmer and wet in > 3.7 b.y.a. <- Huge climate change between Noachian and Hesperian) ± Southern highland: Older craters (from Noachian) have erosion. Lack of smaller craters. Younger craters (from Hesperian and Amazonian) have less erosion. -> supports “wet and warm” Noachian climate. ± Sediments at the bottom of craters <- filled with liquid water. ± Although liquid water is not stable today on the Martian surface, in some case (like catastrophic release of undersurface water) might carve some surface feature. ± [NOT FROM YOUR TEXTBOOK] Two days ago (Dec 06 2006), NASA released a series of images of Mars surface which indicates the possible existence of liquid water on Mars in the past 7 years. (see: http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html ) z The climate history of Mars ± “Wet and warm” Noachian climate ± Need greenhouse effect <- CO 2 , probably some methane. ± CO
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final_review - AST 5: Life in the Universe, Fall 2006, UCLA...

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