1. Today’s APODAPOD  Next: Chapter 9 – Outer Planets  Quiz 7 today  Rooftop on Nov. 10, Kirkwood Nov. 12  Homework due TODAY The Sun Today A100 - Comparing Terrestrial Planets

2. 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

3. Surveying the Red Planet Mars Topography North smooth surface few craters lower elevation ***younger*** South rough surface heavily cratered higher elevation ***older*** Why are the northern and southern hemispheres of Mars so different?

4. Surveying the Red Planet Hypotheses 1.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

5. Surveying the Red Planet Plate Tectonics on Mars? Rising material from the interior creates a “rift” and forms new crust New crust spreads and is “subducted” where convection in the mantle pulls it down Compression features will form where new crust encounters old crust Subduction provides fuel for volcanic activity (Tharsis volcanoes?)

6. Largest Mountain in the Solar System

7. Surveying the Red Planet More evidence for plate tectonics? The crust of mars is thinner in the northern hemisphere When a rift expands quickly, new crust is smooth and thin Plate tectonics cools the interior; when the interior cools off, mantle convection ends, and plate tectonics stop. SN

8. Surveying the Red Planet Magnetic Stripes 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 Surface magnetic field measured by MGS Bands of opposite N/S polarity

9. 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

10. The Atmosphere of Mars  Clouds and wind blown dust are visible evidence that Mars has an atmosphere  Spectra show the atmosphere is mainly CO 2 (95%) with traces of N 2 (3%), oxygen and water  The atmosphere’s density is about 1% that of the Earth’s

11. 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  CO 2 “snow” falls on poles during winter

12. 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

13. Surveying the Red Planet Climate Change on Mars? Modern Cold and Arid Past? Wet and Warm? Percival Lowell first popularized the idea that early Mars was warm and wet

14. Surveying the Red Planet Evidence for Water Ice on Mars Polar caps Surface frost, Viking 2 Ground ice (Mars Odyssey )

15. Surveying the Red Planet Headscarp of Chasma Boreale 1000 m of layered ice, frozen sand dunes, and layered sedimentary rock above a cratered basement

16. Surveying the Red Planet Viking orbiter found channels Martian delta Fossil delta on Earth Evidence for Flowing Water in the Past

17. 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.

18. Surveying the Red Planet Large CO 2 abundance up to ~ 3.8 Gyr allows warm climate and channels ~ 3.8 Gyr: Heavy bombardment removes much of early atmosphere Further loss of CO 2 to carbonate minerals and escape gradually reduces CO 2 to present levels The Martian Atmosphere – Standard Model But – some problems with this model (nitrogen abundance doesn’t match, not enough carbonates on Martian surface)

19. Surveying the Red Planet Alternate Models Transient warmings? –large impacts –thermal events, volcanoes Water features caused by other fluids? Pyroclastic flows Sulfur-rich fluid lavas W. K. Hartmann

20. Comparing the Terrestrial Planets ?

21. 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

22. 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

23. The Role of Biological Processes  Biological processes remove CO 2 from the atmosphere  Sea creatures use dissolved CO 2 in ocean water to make shells of calcium carbonate  Shells fall form sediment on the ocean bottom  Sediment becomes rock, sequesting CO 2  With CO 2 removed, mostly N 2 is left  CO 2 is recycled back into the atmosphere by tectonic activity  Green plants break down H 2 O, C0 2 during photosynthesis, producing oxygen

24. Comparing Planets  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  Earth  Massive  Modest atmosphere  Some vulcanism  Plate tectonics  New crust  Life  Mars  Medium Mass  Thin CO 2 atmosphere  Some vulcanism  Early plate tectonics?  Old and not-so-old crust  Life?

25. ASSIGNMENTS this week  Next Week – Ch 9 – Outer Planets  Rooftop session on Nov. 10  Kirkwood Open Nov. 12  Turn in homework!