Lesson 5

1. Lesson 5 Venus

2. Venus from Earth At its brightest, Venus is about 60 times brighter than the brightest stars.

3. Venus is the morning or evening “star” • Venus is never more than 47 degrees from the Sun.

4. Why does Venus look this way?

5. . • The Earth is casting a shadow on Venus • Mercury is casting a shadow on Venus • We are seeing the day and night side of Venus • There are clouds blocking part of Venus

6. Venus phases • What is Venus’s phase when it is closest to the Earth?

7. . • New Venus • Full Venus • Half-lit

8. When Venus is close to the Earth we only see the night side of Venus. When it is on the other side of the Sun we see the full Venus

9. Galileo was the first to see the phases of Venus, using a small telescope. (1610) • The changing size and phases was proof that Venus didn’t orbit the Earth. Instead, Venus had to orbit the Sun.

10. Venus – Basic Properties

11. Venus – Basic Properties • Diameter is 650 km less than Earth’s • Mass is 81.5% of Earth’s • Virtually a twin to Earth in size and mass. • Venus has no moon • Venus atmosphere is 90 times that of Earth • Surface temperature is ~ 870o F everywhere. • Always under cloud cover

12. Venus rotates on its axis very slowly (225 Earth Days) and in the opposite direction of that of the other planets. • On Venus the Sun would rise in the west and set in the East. • On Venus, a year is 1.92 Venus days long. So if you were on Venus you would have about 2 days each year. • The slow rotation and small differences in surface temperature around the planet means wind speeds are very slow on Venus. Virtually no wind erosion as on Mars.

13. We saw on Mars that there has been a great deal of wind erosion. • Venus has virtually one global temperature with only small variations. • Would you expect Venus to also have lots of wind erosion on its surface?

14. . • Yes. Venus has a thick atmosphere and is very hot. This should cause enormous winds • Yes. Since Venus rotates slowly winds should be able to blow from the poles to the equator • No. There are no temperature differences so wind will not develop.

15. Venus rotates on its axis very slowly and in the opposite direction of that of the other planets. • On Venus the Sun would rise in the west and set in the East. • On Venus, a year is 1.92 Venus days long. So if you were on Venus you would have about 2 days each year. • The slow rotation and small differences in surface temperature around the planet means wind speeds are very slow on Venus. Virtually no wind erosion as on Mars.

16. Venus from outer space

17. Venus is always shrouded in thick clouds. The atmosphere is almost completely carbon dioxide (CO2). • The cloud decks seen from space are composed mostly of sulfur dioxide (SO2). • There is virtually no water in the atmosphere of Venus.

19. Topographical Map

21. Red highest elevation, blue lowest

22. Earth topographical map

23. Earth Active Volcanoes

24. Venus volcanoes

25. Is there plate tectonics occurring on Venus?

26. Is there plate tectonics occurring on Venus? • Yes • No

27. What type of volcanoes do you expect?

28. What type of volcanoes are on Venus? • Strato-volcanoes • Shield volcanoes • A mixture of the two.

30. Venus volcanoes Maat Mons Gula Mons

31. All Venus volcanoes are shield. • Large shield volcanoes • Pancake Domes (smaller, sometimes form along fissures) • Corona (uplifts in crust causing tectonic features) • Arachnoids (spider-like volcanoes that have sunk back into the surface)

32. Large shield volcano

33. Lava Flow and channelsMylittaFluctus

34. Lava Flow and channelsAtlaRegio about 1000 km long

35. Helen PlanitiaLong lava flow channels (~1200 km long) which show signs of being covered by later lava flow.

36. Pancake volcanoes forming in a line along fissure

37. Flat top, pancake domes suggest that the lava was of higher viscosity

38. If pancake domes form along crustal fissures, why might they have higher viscosity?

39. . • There must be a subduction zone that mixes crustal material into the mantle magma. • Mantle magma emerging up through the fissure probably melts the crust which makes the magma of higher viscosity

40. Corona features Caused by hot mantle material uplifting and sinking over and over again.

41. Arachnid volcanoes are probably volcanic domes which sunk back down when magma retreated

42. About 1000 impact craters on Venus

43. Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. • Why do you think this is?

44. . • All the smaller craters are destroyed by geologic activity • Smaller meteors can’t make it through the thick Venus atmosphere • Venus only gets hit by big objects.

45. Distribution of Impact craters

47. Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. This is due to the protection of the extremely thick atmosphere. • The impact craters are randomly distributed across the surface of Venus. • Density is about 1.9 craters/million km2. This is the same everywhere on the surface. • What does this suggest?

48. . • The surface of Venus is the same age globally. • Younger regions on the surface have been hit more frequently in the recent past. • Venus is similar to the highlands of the Moon

50. Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. This is due to the protection of the extremely thick atmosphere. • The impact craters are randomly distributed across the surface of Venus. • Density is about 1.9 craters/million km2 • Lunar density for a 0.9 billion years old surface is 20 craters/million km2