3-1 The moon

1. 3-1 The moon 3-1 The Moon

2. Exploration of the Moon Some imagined seas and inhabitants What is the nature of these features?

3. 1609, Galileo: First to use the telescope to observe the Moon Discovered craters Volcanoes?

4. Spacecraft exploration 1959: Luna 3 returned the first photo of the far side 1966: Luna 9 landed on the surface

5. Most of what we know today derives from the Apollo program (1968 -1972) 9 piloted spacecrafts Landed 12 astronauts on the surface (but only one scientist)

6. Astronauts brought back 400 kg of samples for laboratory analysis (still being studied)

7. Astronauts implanted experiments which continued to operate for years after they departed The orbiting Apollo modules photographed and analyzed the surface from above Cost: 10$ a year for 10 years per American

9. Lunar Prospector Estimated the quantity of water ice on the Moon => at least 6 billion tons (enough to fill lake a few kilometers across) Possibility of future human habitations near the lunar poles Or a lunar base as a way station on the routes to Mars

10. Most visible feature: Maria (plural: Mare) Early names: Mare Tranquillitatis, Mare Nubium

11. Lunar mare

12. The lunar surface Three types of terrain Mare Craters Highlands

13. Maria / Mare Cover 17% of the surface Composed of basalt => volcanic origin Dating of basalt samples => a series of large volcano eruptions took place between 3.3 and 3.8 billion years ago

14. Training: maria or highlands?

15. Maria

16. Highlands Maria

17. Moon craters

18. The Moon is covered in craters of all sizes Far side, Apollo 16

19. On Earth: two kinds of craters Impact crater Volcano craters

20. Volcano or impact? until mid-20th century: “Impact craters are rare on Earth => they cannot be a major feature of lunar geology”

21. Observe carefully the following pictures and compare the features of a volcano crater seen on Earth and moon craters

22. Moon craters Volcano crater on Earth

23. Observe carefully the following pictures and compare the features of an impact crater seen on Earth and moon craters

24. Moon craters Impact crater on Earth

25. Grove K. Gilbert, 1890s: Volcano craters on Earth are: Small and deep Almost always at the top of volcanic mountains

26. While craters on the Moon: Floor below level of surrounding terrain Tycho crater circular mountain-rimmed Archimedes crater

27. Crater rays Copernicus crater Can extend for hundreds or even thousands km from the crater

28. Grove K. Gilbert Lunar craters are impactcraters Conclusion not accepted in his time

29. Animation: water splash Animation: formation of an impact crater

30. Formation of an impact crater An asteroid impacts the surface at very high speed (~3000 km/h) It penetrates 2 or 3 times its size into the surface of the Moon In a few seconds its energy of motion is transformed into a shock wave and heat The heat is so intense that the rocky asteroid is vaporized (becomes gaseous)

31. The impact generates an explosion similar to a nuclear bomb The cavity is initially bowl-shaped but then the crust of the planet rebounds and fills it in. Sometimes a central peak is created Surrounding the rim is an ejecta blanket consisting of material thrown out by the explosion

32. Impact or volcano? impact Crater Copernicus

33. Impact or volcano? impact

34. After World War I : scientists recognize the similarity between impact craters and explosion craters Size of impact crater = 10 to 15 times diameter of projectile

35. The surface of the Moon is buried under a fine-grained soil of tiny rock fragments = “moondust”

36. Astronauts boots sank several centimeters

37. Rilles Ariadaeus

38. How old is the Moon? Notation: 1 billion years = 1 Gyr Moon rocks analyzed by radioactive dating: solidified between 3.3 and 4.4 Gyr ago Moon rocks analyzed by radioactive dating: solidified between 3.3 and 4.4 Gyr ago Highlands consist of rocks 4.1 to 4.4Gyr old Maria: 3.3 to 3.8 Gyr old Why?

39. Why do we see less craters on Earth than on the Moon?

40. On Earth, geological activity is due to the liquid, hot interior of the planet • Mountains rise due to the motion of the tectonic plaques • Lava flows from active volcanoes constantly renew the surface

41. Moon: No more active volcano, no motion of the crust: geologically dead All volcanic activity must have ceased 3 Gyr ago because the Moon’s interior had cooled down By now the interior must be cold, solidified

42. Major mountains are the result of impacts, not of plate motion

43. Moon: no atmosphere => no wind, no rain, no erosion If mountains are rounded, it is because that is the way they were formed

44. Craters stay intact, same as they were 3 Gyr ago = memory of the solar system Rule: older lands are more cratered than recent ones That’s why highlands are more cratered than mare (maria-s)

45. Which crater is the youngest?

47. On the Moon, craters can only be “eroded” by younger craters

48. Using crater counts We know the current abundance of asteroids that can impact the Moon so we can estimate that the Moon is likely to experience: • One 1 km crater every 200,000 years • One 10 km crater every few millions years • One or two 100 km crater every billion year Mathilde

49. How old is that terrain? 2 billion years 100 km

50. Two 100km wide craters At least 2 billion years old 100 km