CH6 - Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson...

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Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson & McMillan, Astronomy Chapter 6 The Terrestrial Planets The Inner Planets The Mercury Mercury Venus Venus Earth (and Moon) Earth Mars Mars The Inner Planets: The Similarities The inner planets are similar to each other and The the Moon: the Made of similar material (rocky mantle around an iron/nickel core) around Formed at a similar time 4-5 billion Formed billion years ago years The Inner Planets: Starting Differences Starting 1. Masses 1. 2. Orbital distance to the Sun 2. Planet Mercury Venus Earth (Moon) Mars Orbit 0.4 AU 0.7 AU 1 AU 1.5 AU Mass 0.055 Earth 0.82 Earth 1 (0.012 Earth) 0.11 Earth Inner Planets, Inner Effects due to Mass As discussed for the Earth and Moon, As mass is very influential for a planet: mass Ability to hold atmosphere and things that evaporate (e.g. water) that Amount of internal heat: volcanoes, plate tectonics and magnetic fields plate Inner Planets, Inner Effects due to Orbits Distance from the Sun Distance affects: affects: How strong Solar tides are tides How much solar heating the planet receives receives Orbits and Rotation Orbits Mercury: Slow forward spin, Mercury: Nearly tidally locked Venus: Spins slowly backwards Venus: Mars: Similar Spin to Earth, 24.6 hour day 24.6 Mercury’s Mercury Long Day Long Close to the Sun: Solar tides tried to synchronise orbit and spin synchronise Orbit is elliptical: Orbit didn’t quite work 3:2 ratio, 3:2 88 day orbit : 59 days to spin Schiaparelli: Visual Modern: Radar Venus Retrograde Venus (Backward) Spin Only inner planet to spin backwards backwards Somewhat unexpected Somewhat Favoured iidea: By chance last Favoured dea: big impact struck so as to leave almost no spin almost Long day: 243 Earth Days and and Sun rises in the West Planet Atmospheres? Planet Escape Velocity Mercury Venus Earth (Moon) Mars 4.3 km/s 10.4 km/s 11.2 km/s (2.4 km/s) 5.0 km/s vs. vs. Atmosphere gas Particle speed Particle Hydrogen: 2.7 km/s at 27 C • Faster if hotter • Slower if heavier gas Atmospheres Mercury: None Mercury: Venus: Thick, mostly Carbon Dioxide, Clouds (Sulphuric Acid), no water Clouds Earth: Nitrogen, Oxygen Earth: Mars: Thin, mostly Carbon Dioxide, small amounts of water small Surface Temperatures Surface Atmosphere insulates the planet to keep Atmosphere surface temperatures warmer and more uniform uniform Mercury: 125 K to 700 K Mercury: Venus: around 740 K Venus: Earth: 290 K (17 C) Earth: Mars: around 180 to 270 K Mars: Surfaces: Impacts from space Surfaces: All planets have been subject to meteorite impacts meteorite Mercury with no atmosphere is like the Moon: heavily cratered Moon: Erosion or volcanic activity erase evidence of impacts evidence Mercury’s Mercury Surface Mercury’s surface is heavily Mercury surface cratered cratered It has been geologically dead for a long time for Evidence for ancient lava flows (like lunar mare) (like It includes “scarps” wrinkle wrinkle like cliffs (Moon does not) like Surface of Venus Surface Not visible through Not atmosphere: use Radar maps Radar Similar range of heights heights (around 10 km) Height is related to surface gravity surface Surface of Venus Surface No plate tectonics No Volcanoes occur but are large and flat: Shield volcanoes Shield (like the island of Hawaii) (like Russian Venera Lander Venera Surface of Mars of The “Canals” The Of Mars? Grand Canyon: Vallis Marineris Martian Civilizations? Martian Lowell’s 1895 Canal Map Earth-based Observation 1991 The Real Mars The Desert planet Desert Red colour is from iron oxides (rust) colour Dark and Light patches move due to regular dust storms regular Mars Impact Craters Shield Volcanoes Shield Olympus Mons: Olympus Largest volcano in the Solar Largest System System Water on Mars? Water Dry River valleys, channels Dry “Splosh” craters Rounded rocks Rounded BUT: Last 3 Billion years: water locked up as permafrost locked Seepage: Very recent evidence of a permafrost layer? permafrost Narrow Narrow channels channels iindicative ndicative of low viscosity fluid like water water Still wet? (weeping) New darker material Mars Global Surveyor 2000 landslide? Seepage Channels Mars Water: Mars Ice in Craters If sheltered from direct sunlight water ice can persist ice Plenty of ice in high latitude (near poles) latitude Phoenix Lander 2007-2010 2010 70o N (frozen) 70 ESA Mars ESA Express 2005 Express Life on Mars? Life Viking probes tested for biological responses (inconclusive: perchlorate) perchlorate Biological fossil marks in Martian meteorite? Unlikely Mars Landers Mars Viking Viking 1970’s 1970 Sojourner & Sojourner Pathfinder 1997 Pathfinder Mars Landers: Jan 2004 Spirit Rover Jan Rovers can move and dig Rovers Measure chemical and mineral components mineral Microscope Microscope Atmospheres revisited Atmospheres Mercury: None (a little temporary Mercury None solar wind Hydrogen and Helium) solar Venus: 90 times Earth pressure Venus 90 Mostly Carbon Dioxide Earth: 1 Earth Pressure Earth Mostly Nitrogen, Oxygen, trace Carbon Mostly Dioxide Dioxide Venus Mars: 1/150th Earth Pressure Mars Mostly Carbon Dioxide Where did the gas come from? from? The Solar Nebula provided a little gas to the inner planets the Mostly Hydrogen and Helium This gas escaped This The current secondary atmospheres are secondary atmospheres due to outgassing outgassing Atmosphere: Atmosphere: Outgassing Planet interior rock chemistry produces gases: Carbon Dioxide, Water, Nitrogen Compounds, Sulfur compounds … Volcanoes release these gases into the atmosphere atmosphere All the inner planets produced an atmosphere this way (but only Venus and Earth could keep it) (but Atmospheres: Atmospheres: Earth vs. Venus Earth and Venus once had similar very Earth thick atmospheres with: thick Lots of Carbon Dioxide Some water vapour vapour What happened? Earth’s atmosphere Earth The initial Greenhouse effect was stronger than now but not by too much stronger Liquid water formed oceans Liquid Carbon Dioxide other compounds dissolved and formed rocks, Nitrogen gas was released gas Earth’s Atmosphere: Earth A special Ingredient: Life 3.5 Billion years ago microscopic life began photosynthesis on Earth began Photosynthesis results in a small net production of Oxygen (from Carbon Dioxide) Dioxide) Earth’s Current Atmosphere: Earth 78% Nitrogen 21% Oxygen Venus’ Atmosphere Venus Venus is closer to the Sun Venus Venus gets twice as much solar heating as Earth heating Carbon Dioxide and Water vapour iin Venus atmosphere vapour n prevent the Infrared escaping easily easily Venus got hotter than Earth… Venus Venus’ Atmosphere: Venus Runaway Greenhouse Effect Venus’ Atmosphere: Venus Runaway Greenhouse Effect Venus never had oceans remove its Carbon Dioxide Carbon Venus got so hot it evaporated or never formed oceans formed Venus Greenhouse Effect ran away until the surface temperature hit 730 K ( 500 C) Mars’ Atmosphere Mars Mars once had an atmosphere, liquid water and maybe even blue skies water It lasted perhaps 1 billion years It Atmosphere was lost Atmosphere No greenhouse heating: Mars cooled No The water froze or was lost as gas The Inner Planets and Martian Moons Martian Only Earth has a large Moon Only Mars is the only other with moons: Mars Diemos and Phobos Diemos and Phobos More or less just asteroids More ...
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