1. Venus and Mercury

2. The Inner Planets

3. Venus Only a bit smaller than Earth Nearest planet (26 million miles) Shows phases as it orbits the Sun Most circular orbit Atmosphere mostly Carbon Dioxide –90 times as dense as Earth –Runaway Greenhouse Effect –Surface Temperature 450 C (850 F)

4. Venus’ Odd Rotation Venus Rotates in 243 days relative to the stars Longer than its year (225 days) Solar Day = 117 days You can jog as fast as Venus rotates Opposite to all other planets’ rotation (retrograde) Why? –Mega-Impact? –Tidal Effects? –Possible tidal lock on Earth?

5. Venus from Pioneer Venus Orbiter

6. Polar View of Venus

7. Topography of Venus

8. Earth Elevations

9. Radar Map of Venus

11. Surface of Venus

12. Venus has Craters

13. Venus is Volcanic

14. “Pancake” Volcanoes

15. Channel on Venus

16. Coronas

17. How Coronas Form?

18. Venus Differs from Earth in One Important Way: Venus has no Plate Tectonics Earth’s internal heat causes hot material to rise within Earth and plates to move Venus’ crust is too rigid Heat builds up and escapes in planet-wide volcanic activity Last event about 600 million years ago

19. Why Venus Has No Plate Tectonics It’s Hot! We’d expect hot rocks to be less rigid, not more! But it’s also dry! Dry rocks are ten times stronger at high temperatures than wet rocks. Earth is wet. That affects not just the outside, but the inside as well.

20. Did Venus Once Have Oceans? Resurfacing means no visible trace of early history Deuterium: Ghost of a Vanished Ocean? –Deuterium is hydrogen with one neutron –Twice as heavy as normal hydrogen –Less likely to escape –D/H on Venus 100x that of Earth Photodissociation + Stripping –Venus lacks magnetic field

21. Venus and the Da Vinci Code 13 Venus years = 13 x 224.7 = 2921.1 days 8 Earth Years = 8 x 365.25 = 2922 days 5 Synodic periods of Earth and Venus = 5 x 583.9 = 2919.5 days 1/5 of a circle = 72 degrees In 583.9 days, Earth moves 360 + 215.5 degrees (almost 360 + 3 x 72) In 583.9 days, Venus moves 720 + 215.5 degrees

22. Venus and Earth 13 Venus years = 13 x 224.7 = 2921.1 days 8 Earth Years = 8 x 365.25 = 2922 days 5 Synodic periods of Earth and Venus = 5 x 583.9 = 2919.5 days 12 Venus rotations = 2916 days Venus shows nearly the same face to Earth every 584 days.

23. Venus and Earth

24. Mercury Closest planet to Sun Very elliptical orbit (e =.205) Only 3000 miles (5000 km) in diameter Rotation locked to Sun: 3 rotations in 2 orbits (58 days) Moon-like on the outside (craters) Earth-like on the inside (dense core, magnetic field)

25. Mercury’s Rotation

26. Mercury’s Interior Density = 5.43 (Earth = 5.5) Much smaller than Earth, less pressure inside Core about 2/3 of Mercury’s diameter (Earth = ½) Mega-Impact may have blown away silicate outer part

27. Mercury from Mariner 10, 1973

28. Mercury has Craters Not as dense as on Moon Most of Mercury covered with lava plains (intercrater plains)

29. Mercury has a huge impact basin, the Caloris Basin

30. Because of Mercury’s locked rotation, it has two “hot poles”

31. And Mercury has the last thing you’d expect to find: ice caps

32. Mercury’s ice seems to be hiding in polar craters

33. We’re B-a-a-ck

35. “Spider” Crater

36. Caloris Basin

37. Volcano on Mercury