Mercury

1
Mercury
Best Ground-based Photo
2
Mercury

• Observing Mercury from Earth is very difficult,
  at
• most 28o from the Sun. Even rotation period not
• known until 1965.

• Orbital period 88 days

• 1965 Radar was used to determine rotation
  period
• Rotation period 58.7 days, exactly 2/3rd
  orbital
• period ? Mercury locked into 3-2 spin-orbital
• coupling.

3
3-2 Spin-Orbit Coupling
4
In 1974, Mariner 10 made three flybys of
Mercury, and photographed 45 of its surface.
These photographs revealed that Mercury is very
much like the Moon, except for more extensive
intercrater plains, and the lack of large flat
lava beds called maria.
5
Mercury
Moon
Moon
6
Moon
Intercrater Plains on Mercury
7
Caloris Basin
Opposite Caloris Basin
8
(No Transcript)
9
Mercury has almost no atmosphere.
The daytime average temperature is 350C The
nighttime average temperature is 170C The peak
dayside temperature is 550C
however, Mercury does have polar ice caps!
10
Radar Image of Mercury, showing Ice Cap
11
Magnetic Field
Mercury has a large iron core like the Earth, but
a much weaker magnetic field.
The reason the rotation rate is very slow,
meaning that the dynamo effect is very weak.
12
The Moon
13
The Moon
Diameter about ¼ that of the Earth Mass
about 1/80 M? No atmosphere, synchronous
rotation (1-1 spin-orbital coupling).
14
Land Types

• Maria Lava Plains 15
• Cratered Highlands 85

Age of the Maria 3.1 3.8 Billion
years Highlands 4.0 4.3 Billion years
15
Far Side
Moon Near Side
16
Lunar Maria
17
Lunar Highlands
18
(No Transcript)
19
Moon rocks have a similar composition to Earth
rocks except for slightly higher proportions of
refractory materials Moon formed at a higher
temperature.
20
We believe the Moon was formed from the
collision of a Mars-sized object with the Earth.
21
Collisional Formation of the Moon from the impact
of a Mars-sized body with the Earth
22
A Brief History of the Moon
1) Formation 4.5 4.6 billion years ago
2) The Great Bombardment 3.8 4.5 billion
yrs ago
3) Formation of the Lunar Maria, 3.1 3.8
billion yrs ago.
4) Nothing much has happened for the last 3
billion years!