The Moon

1
The Moon
2
Physical Properties of the Earth and Moon
3
Why does the moon have no atmosphere while the
Earth does?
A gas will be retained by a planet for billions
of years only if its escape velocity is at least
10 times as great as the average velocity of a
molecule of the gas.
k 1.3810-23J/K T the absolute temperature m
the mass of the molecule.
G 6.6710-11 Nm2/kg2 M planets mass R its
radius
ExampleThe mass of an oxygen molecule is
5.310-26 kg. Assuming that the moons
temperature is 1300C, show that it is incapable
of retaining water vapor for billions of years.
4
Terminology

• Terminator
• Mare
• Sinuous rille
• Basalt
• anorthosite
• breccia
• Vesicular basalt
• Regolith
• Ejecta
• Jumbled terrain
• Lava tube

5
Lunar Surface
6
Clementine Discovery of Lunar Ice?
7
Lunar Interior
Crust
Mantle
Core

• Moonquakes Apollo 12, 14, 15, and 16.
• Gravity Mapping Lunar orbiters
• Crust thickness average is 70 km, thicker under
  highlands
• Core radius between 300 and 450 km.

8
Mare Orientale

• 900 km in diameter.
• 3 billion years old.
• Straddles the boundary between the near side and
  the far side of the moon.
• Surrounded by rings due to ripples from the
  impact of the asteroid that created it.
• Diametrically opposite this is a region of
  jumbled terrain, where the seismic waves from
  the impact were focused and broke up the crust.

9
Hadley Rille

• 125 km long
• 1500 m wide
• 300 m deep
• 3.3 billion years old
• Result of a stream of lava that melted a channel
  through the mare surface, possibly a lava tube
  that eventually collapsed.
• Located on the southeast edge of Mare Imbrium.
• Arrow indicates the landing site of Apollo 15.

10
Tycho

• Why are most craters round?
• Why does a crater usually have a mountain peak at
  its center.
• Where is the Sun relative to the moon when this
  picture was taken?

11
Copernicus
Why are there light-colored rays extending
outward from the crater?
12
Mare Imbrium
13
Locations of the Lunar Maria
Animated Moon Map
14
Why is there no tectonic action on the moon?
Although the moon was once in a molten state, it
cooled and solidified much faster than earth
because of its small size and mass.
The cooling time of any object is proportional to
its radius and its mass density.
Earths radius and density are both greater than
those of the moon. Consequently, the moon cooled
a lot faster than earth did. It solidified before
tectonic action could occur.
15
Origin of the Moon

• Fission (due to rapid spinning of earth) no.
• Condensation (as a double planet system with the
  same composition) no.
• Capture (due to earths gravity) no.
• Large impact probably.

• Large planetesimal (about twice the mass of Mars
  ?) collides at a glancing angle with proto-earth.
• Heat of impact melts the system.
• Most metals sink to form earths core.
• Spin-up results in formation of disk.
• Disk would be deficient in metals and volatiles.
• Condensation and accretion in the disk would form
  the moon.