The Near Side Megabasin of the Moon

1. The Near Side Megabasin of the Moon • Presented to Star Astronomy • May 1, 2008 • By Charles J. Byrne • Image Again • charles.byrne@verizon.net • www.imageagain.com • With topographic views from Nick Lordi

2. The Early Moon • A Mars-sized body, its orbit perturbed, collided with Earth, 4.5 Billion years ago. • This body, and part of Earth’s crust, were vaporized and formed a ring around Earth. • Soon, this ring cooled, and the Moon accumulated. • The heat released by gravity formed a magma ocean.

3. Crystallization of the Early Moon

4. Asymmetry of the Current Moon • The “Man in the Moon” (maria) is mostly on the near side • The near side is low, a bulge on the far side • The crust is thin on the near side, thick on the far side • Heavy element anomalies are mostly on the near side • Uneven moments of inertia: offest C. G.

5. Near Side of the Moon

6. Far Side (Nozomi)

7. Eastern Limb (Lunar Orbiter)

8. Eastern Limb (Apollo 16)

9. Maps of the Current Moon • Topography • Photography (photometry and stereo) • Laser and radar altimeters • Gravity potential • Tracking of spacecraft • Crustal thickness: inferred from topography and gravity • Mineral concentrations

10. Clementine Elevation Map -5000 m 0 m 5000 m

11. Why? • Asymmetric impacts? • Uneven crystalization of the magma ocean? • Tidal effects in a complex early orbit?

13. Impact Dynamic Tutorial • Incoming asteroids and comets • Hypervelocity impacts: explosions • Cavity formation • Ejected target material • Formation of rings • Effects of target curvature • Scaling laws

15. Lunar Basin (Orientale)

16. Orientale, LIDAR and ULCN (Lordi)

17. Noise Reduction for ULCN (Lordi)

18. Orientale, ULCN (Lordi)

19. Orientale, radial profile

20. Simulation of Impacts

21. Radial Profile of Selected Basins

22. Profile of Ejection Velocity

23. Curvature of the Target • A giant basin must consider the spherical nature of its target • Ejecta is thrown into elliptical orbit • There is less area for the ejecta to land near the antipode, so it piles up

24. Steps in Making the Model • “Flat Moon” basin model • Ejection velocity radial profile • Orbital trajectory equations • Focusing effect of the spherical Moon • Final radial profile of ejecta

25. The Search • The scaled model has these parameters: • Latitude and Longitude of center • Diameter • Depth • Parameters were varied to make a best fit • Started with two large basins • They grew as the fit improved • They merged into one giant basin

26. Model of the Near Side Megabasin

27. Escaping ejecta (hyperbola) Escape velocity 600 km impactor

28. Velocity less than escape Transient crater expands Ejecta passes antipode

29. Velocity falls further Ejecta is concentrated at antipode Antipode

30. Ejecta falls between basin rim and antipode Velocity falls further

31. Radial Profile of the Near Side Megabasin

32. The NSM Floor is Refilled with Crust

33. Refilling of Plastic Crust

34. Model of the Moon with the NSM

35. The NSM and its Antipode

36. NSM and Titanium

37. NSM and Iron

38. NSM and Thorium

39. NSM and Maria

40. NSM Rim on the Far Side

41. NSM Rim at Tsiolkovskiy

42. Summary • The history of the Moon from its origin to today has been reviewed • Its original crust has been strongly modified by impacts, starting with the NSM and SPA. • 4 billion years of bombardment followed • The major mineral anomalies on the surface are associated with the impacts of the NSM and SPA.