1. Unraveling the History of the Moon

2. The Lunar Surface Maria Highlands low density rocky slag formed on top
of molten Moon
heavily cratered
Maria
17% of Lunar surface
Huge lava flows from volcanoes
Basalts - similar to volcanic rock on Earth
but no water
fewer volatile (= easily melted) elements.
Much less iron.

3. Crater Bullialdus

4. Craters as Chronometers
The number of craters on a surface can be used to estimate its age: older surfaces have been exposed to impacts for longer and show more craters

5. Complications Any changes in the impactor population over time
Secondary impacts formed by ejecta from a single large impact
Saturation: when a surface is so heavily cratered that a new crater can form only at the expense of an older one
There is a need for measured surface ages in order to calibrate the crater counting

8. Solid line: trend for southern highlands Dotted points: average for Maria

9. Calibrating the rate of lunar cratering
Moon rocks (mostly recovered during the Apollo missions but a few by the Soviet Luna probes)

10. Dating Rocks Radioactive elements U-235 half-life = 710 million years
U-238 half-life = 4.5 billion years
Th-232 half-life = 13.9 billion years

13. Ages of lunar features
Heavily cratered highlands: billion years old
Large basins: 3.9 – 4.1 billion years old
Maria flooding: 3.0 – 3.9 billion years old
Compared to the Earth, the typical lunar surface is very ancient

14. High early cratering rate

15. Late heavy bombardment?
A proposed interval about 3.8 to 4 billion years ago in which the moon and the inner solar system were subjected to heavy asteroid bombardment
Time of the formation of impact basins?

18. The crust facing the earth may be thinner than on the farside

20. The Interior of the Moon
Most maria are on near side.
Center of mass offset 2 km towards Earth.
Earth
Crust is 107 km thick on far side.
Crust ~ 0 km thick on near side.
From Modern Astrophysics, by Carroll & Ostlie.
3476 km
Geologically inactive.
No magnetic field  no molten core.