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A100 - Comparing Terrestrial Planets Next: Chapter 9 – Outer Planets Quiz 7 today Rooftop on Nov. 10, Kirkwood Nov. 12 Homework due TODAY Today’s APOD The Sun Today The Martian Interior Differentiated like the Earth’s interior into a crust, mantle, and iron core Having a mass between that of dead Mercury and lively Earth/Venus implies Mars should be intermediate in tectonic activity Numerous volcanic peaks and uplifted highlands exist Olympus Mons and other volcanoes do not show any craters on their slopes indicating they may still occasionally erupt Surveying the Red Planet Mars Topography Why are the northern and southern hemispheres of Mars so different? North • smooth surface • few craters • lower elevation • ***younger*** South • rough surface • heavily cratered • higher elevation • ***older*** Surveying the Red Planet 1. Hypotheses Did a major impact (or several large impacts) resurface the northern hemisphere? NO - Not circular, no rim… 2. Did an ancient ocean in the northern hemisphere eroded away the surface, erasing the craters? NO - No shoreline, slopes not consistent, features at boundary suggest compression Surveying the Red Planet Plate Tectonics on Mars? New crust spreads and is “subducted” where convection in the mantle pulls it down Compression features will form where new crust encounters old crust Rising material from the interior creates a “rift” and forms new crust Subduction provides fuel for volcanic activity (Tharsis volcanoes?) Largest Mountain in the Solar System Surveying the Red Planet More evidence for plate tectonics? The crust of mars is thinner in the northern hemisphere S N Plate tectonics cools the interior; when the interior cools off, mantle convection ends, and plate tectonics stop. When a rift expands quickly, new crust is smooth and thin Surveying the Red Planet Magnetic Stripes • Surface magnetic field measured by MGS • Bands of opposite N/S polarity • Mars once had a reversing magnetic field – a core dynamo like Earth’s • Evidence of mantle convection and plate tectonics • Dynamo ended about 4 billion years ago, before the interior cooled Surveying the Red Planet Mars Topography • A mixture of old and “really old” terrain • Evidence suggests that plate tectonics resurfaced the northern hemisphere early in martian history Linear shape of Valles Marineris suggests it was a rift formed through plate tectonics The Atmosphere of Mars Clouds and wind blown dust are visible evidence that Mars has an atmosphere Spectra show the atmosphere is mainly CO2 (95%) with traces of N2 (3%), oxygen and water The atmosphere’s density is about 1% that of the Earth’s Not a drop of rain… No rain falls, despite clouds Atmosphere is too cold and dry Fog seen in valleys and ground frost has been observed CO2 “snow” falls on poles during winter Ancient Atmosphere of Mars Dry river beds indicate liquid water flowed in Mars’s past This implies that Mars had to have a denser atmosphere (higher pressure) to prevent the fast vaporization of surface water into the atmosphere Cratering indicates that this thicker atmosphere disappeared about 3 billion years ago Surveying the Red Planet Climate Change on Mars? Percival Lowell first popularized the idea that early Mars was warm and wet Past? Wet and Warm? Modern Cold and Arid Surveying the Red Planet Evidence for Water Ice on Mars Polar caps Ground ice (Mars Odyssey) Surface frost, Viking 2 Surveying the Red Planet Headscarp of Chasma Boreale 1000 m of layered ice, frozen sand dunes, and layered sedimentary rock above a cratered basement Surveying the Red Planet Evidence for Flowing Water in the Past Viking orbiter found channels Martian delta Fossil delta on Earth Surveying the Red Planet Two Causes of Climate Change • Orbital and axial variations • Long-term evolution Mars is closer to the sun during its southern summer and further from the sun during the northern summer. The southern summer is shorter and hotter, while the northern summer is longer and cooler. The difference affects polar ice loss, weather patterns, and dust storms. Surveying the Red Planet The Martian Atmosphere – Standard Model • Large CO2 abundance up to ~ 3.8 Gyr allows warm climate and channels • ~ 3.8 Gyr: Heavy bombardment removes much of early atmosphere • Further loss of CO2 to carbonate minerals and escape gradually reduces CO2 to present levels But – some problems with this model (nitrogen abundance doesn’t match, not enough carbonates on Martian surface) Surveying the Red Planet Alternate Models • Transient warmings? – large impacts – thermal events, volcanoes W. K. Hartmann • Water features caused by other fluids? • Pyroclastic flows • Sulfur-rich fluid lavas Comparing the Terrestrial Planets ? Role of Mass and Radius Mass and radius affect interior temperature This in turn determines the level of tectonic activity Low-mass, small-radius planets will be cooler inside and hence less active than larger planets This relationship is in fact observed with Mercury (the least active), then Mars, then Venus/Earth The Role of Sunlight Warming from sunlight depends on the planet’s distance from the Sun – the closer the warmer Warming also depends on the amount and makeup of the atmosphere Solar warming and atmospheric chemistry also determines the structure of the atmosphere, which may affect the amount of warming On warmer Venus lifts water vapor to great heights in its atmosphere On cooler Earth, water condenses out at lower heights and the upper atmosphere is almost totally devoid of water The Role of Biological Processes Biological processes remove CO2 from the atmosphere Sea creatures use dissolved CO2 in ocean water to make shells of calcium carbonate Shells fall form sediment on the ocean bottom Sediment becomes rock, sequesting CO2 With CO2 removed, mostly N2 is left CO2 is recycled back into the atmosphere by tectonic activity Green plants break down H2O, C02 during photosynthesis, producing oxygen Comparing Planets Earth Mercury Low mass No atmosphere No plate tectonics Old crust No life Venus Massive Extensive atmosphere Active vulcanism? New crust No plate tectonics No Life Massive Modest atmosphere Some vulcanism Plate tectonics New crust Life Mars Medium Mass Thin CO2 atmosphere Some vulcanism Early plate tectonics? Old and not-so-old crust Life? ASSIGNMENTS this week Next Week – Ch 9 – Outer Planets Rooftop session on Nov. 10 Kirkwood Open Nov. 12 Turn in homework!
