Terrestrial Worlds: Mercury, Venus, and Earth - A Comparative Look

1. Terrestrial Worlds 1 Mercury

2. Mercury • 1974 -Mariner 10 flyby • 2008-Current -MESSENGER

3. Mercury’s Surface What is the most common process on mercury?

4. Mercury’s Surface • A mixture of heavily cratered and smooth regions like the Moon • Smoother regions are likely ancient lava flows

5. Caloris basin‏ Multi-ring impact basin (Only half visible from Mariner 10)‏

6. Caloris basin MESSENGER 2009 -1550km

7. Volcanism on Mercury • ancient lava flows, no large floods

8. Tectonics on Mercury Cooling causes shrinkage causing fault scarps (cliffs)‏

9. Mercury Atmosphere • 10-14 bars of pressure (negligible)‏ • Gas comes from impacts that eject surface atoms Mercury • Temperatures: 800 oF in day (second hottest)‏ -300 oF at night

10. Terrestrial Worlds 2 Venus,

11. Venus basics • 2nd planet from Sun (0.7 AU), 6th largest world. • Orbit -224 Earth days • Sidereal rotation -243 Earth days (solar day-117 Eds)‏ • Surface gravity-8.8 m/s2 (90% of Earth)‏ • Intense cloud cover - highly reflective in visible light, surface unseen except by radar • Spacecraft- Pioneer, Magellan (USA)‏ Venera 9-16 (Russia)‏

12. Highlands on Venus- Aphrodite Terra

13. Venus - Chasma Vast mountain and canyon systems. -3km high and 3km deep running for thousands of miles

14. Venus- Regios Regions Where canyon systems join at a high volcano

15. Tectonics • Upwelling -Extension rifts at hot spots = chasmas and regios • Downwelling -Highlands and faulted regions called tessera Crust too strong to break all the way through. No plate tectonics

16. Volcanism on Venus • 80% of Venus is resurfaced by volcanism • Volcanic shapes controlled by height and location. • Hot spots -large shield volcanoes. • Lowlands - volcanic floods. • Middling heights- fields of cinder cones. • High areas - lava too hard to rise - coronae

17. Venus Surface Processes - Wind Wind streak showing wind direction

18. Venus Cratering • Lots of small to middle-sized craters, few large ones • Even distribution -Most of Venus’ surface has a similar age • Most of Venus resurfaced by catastrophic lava flooding < 1 billion yrs ago. • Current activity??

19. Venus Atmosphere • 90 bars of pressure (90 x Earth)‏ • 96% CO2 3.5% N2 < 1% others • Massive greenhouse warming. • Venus is the hottest planet. 870 oF • Clouds- sulfuric acid! • Slow rotation - almost no coriolis effect.

20. Terrestrial Worlds 3 Earth - The most unique of all

21. Earth basics • 3rd planet from Sun (1 AU), 5th largest world • Orbit - 1 Earth year • Sidereal rotation - 23.9 hours (solar day -24 hrs)‏ • Surface gravity- 9.8 m/s2. • 1 bar of pressure • 78% N2 21% O2 < 1% others 0.003 CO2. • Temperatures- ~100oF summer (max. 140oF, deserts)‏ - ~0 oF winter (min. -130 oF, poles)‏

22. Unique Features • oceans, • Plate tectonics • oxygen atm. • Life!

23. Earthquakes Detected earthquakes form lines

24. Earth’s crust broken into pieces ~8 large and 10 small plates

25. Crust follows Convection Currents • Falling current drags plate after it. • 1 plate hits another and sinks. • CONVERGENT boundary • Rising current (hot)‏ • Plate dragged aside • Breaks at weakest point (where it is hottest)‏ • New lava wells into gap. • DIVERGENT boundary

26. Earth -tectonics • All a consequence of internal convection: • Extension faults occur at upwelling of mid-ocean ridges (divergent boundary)‏ • Compression faults occur at downwelling of subduction zones (convergent boundary)‏ • Strike-slip faults occur as plates jostle around,

27. Earth -Volcanism • All a consequence of internal convection: • Low viscosity lavas occur at upwelling of mid-ocean ridges -shield volcanoes • High viscosity lavas occur at subduction zones as crust is remelted - tall, explosive, stratovolcanoes Result: Earth is the ONLY world to have stratovolcanoes, because it’s the only world to have plate tectonics

28. Lava erupted at the mid ocean ridge

29. Stratovolcano on continent side of subduction zone

30. Earth - Erosion & Surface processes • Mass wasting • Wind -deserts • Biological (unique) • Water -main process • River Channels erode at head, deposit at mouth • Materials move along beaches • Glaciers grind material down

31. Earth -Cratering Earth has about 200 craters at the surface.

32. Earth’s Volatiles(atmosphere and hydrosphere)‏ • Earth is unique in that: • the majority of it’s volatiles are liquid. • Atmospheric composition is not all CO2(78% N2 , 21% O2 ,<1% others, 0.003 CO2 )‏ • Life affects the atmospheric balance.

33. Earth Oceans and Temperature • Why does Earth have oceans • while Venus and Mars do not? • Earth is the right temperature to have liquid water due to distance from the Sun. • Temperatures are maintained by moderate greenhouse warming • CO2 balance maintained by oceans and life • (they act as a sink for all the CO2 that would otherwise be in the atm. making extra warming)‏ • Magnetic field prevents H2O breakup.

34. Why Does Earth have a Nitrogen/Oxygen Atmosphere? • Most of the CO2 is locked up. Nitrogen is the main ingredient left. • Plant life produces oxygen, as plants increase oxygen levels increase. Large excess over time. • Some of excess oxygen gets broken and remade into ozone • (3 O2 molecules become 2 O3)‏

35. Terrestrial Worlds 4 Our Moon

36. Moon basics • Earth’s nearest neighbor , 14th largest world • Orbit -27.3 Earth days • Sidereal day -27.3 Earth days • Surface gravity -1.61 m/s2 (16% of Earth)‏ • No global magnetic field • Only world visited by humans

37. Compare and contrast the 2 sides of the Moon Near Side Far Side

38. Maria make up 16% of the Moon’s surface and almost all of them are on the Near side

39. Main lunar materials • White highlands • Anorthosite (a rock full of white feldspar)‏ • Dark maria • Basalt (black from iron content)‏

40. Volcanism – Maria Formation • fluid basalts make flood plains that fill large craters • All occur early in lunar history, 3.8-3.2 billion yrs ago Large impact crater weakens crust Heat build-up allows lava to well up to surface Cooled lava is smoother and darker than surroundings

41. Impact cratering is dominant process

42. Surface Processes • Mass Wasting • Radiation damage

43. Moon vs. Mercury What do you think is similar about them? What is different?

44. What processes shaped our Moon? • Early cratering still present • Maria resulted from early volcanic floods • no shrinkage scarps • What processes shaped Mercury? • Cratering similar to Moon, • some volcanism, but no large floods • Shrinkage scarps

45. Moon Formation • Early Theories: Capture, Co-formation(twin), broken off from Earth (fission). • Chemistry of Moon rocks show Moon is both like and unlike Earth • Result: Impactor Theory • Moon formed by a giant asteroid striking a glancing blow on the Earth

46. Impactor Theory Giant impact stripped matter from Earth’s crust Stripped matter began to orbit Then accreted into Moon

48. Lunar Atmosphere • 10-14 bars of pressure (negligible)‏ • Gas comes from impacts that eject surface atoms Moon • Temperatures 225 oF in day -243oF at night

49. Why are smaller terrestrial bodies such as Mercury or the Moon "geologically dead"? • A. They don't have volcanoes. • B. They cooled off faster than Earth did. • C. They don't have erosion. • D. They were hit by fewer meteorites than Earth.

50. Terrestrial Worlds 5 Mars