Topic 5: The Terrestrial Planets and Terrestrial Worlds
Reading:
Earth and the Terrestrial Planets, Chapter 7
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We next consider the Terrestrial
planets. We will concentrate on their:
- interiors
- surface features
- atmospheres
We define a Terrestrial planet as an
object density greater than
2.5 grams per cubic centimeter (cc) and a
diameter
greater than 2,000 kilometers. Our definition is loose and
so the Terrestrial planets include the objects
Mercury
,
Venus
,
Earth
,
the Moon
,
Mars
,
and the Galilean moons Io, and Europa.
Properties of the Terrestrial Planets
Property |
Mercury |
Venus |
Earth |
Mars |
Moon |
Io |
Europa |
M/ME |
0.055 |
0.825 |
1 |
0.107 |
0.0123 |
0.0149 |
0.008 |
R(km) |
2,439 |
6,051 |
6,371 |
3,390 |
1,738 |
1,815 |
1,569 |
T(F) |
662,-274 |
900 |
70 |
70,-100
(equator in summer) |
266,-292 |
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Atmosphere (%) |
|
CO2,96;N2,4 |
N2,79;O2,21 |
CO2,95;N2,3 |
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P(bars) |
|
90 |
1 |
0.0065 |
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ρ(g/cm3) |
5.44 |
5.25 |
5.51 |
3.93 |
3.34 |
3.55 |
2.95 |
Interior (%) |
Fe,70;O,Si,Mg |
|
Fe,35;O,30;Si,15;Mg,13 |
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μ(c.g.s) |
2.4x1022 |
<4x1021 |
8x1025 |
2.5x1022 |
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INTERIORS OF THE TERRESTRIAL PLANETS
We will first discuss the Earth and the Moon
because these two objects should bracket the types of possible behavior
(the Earth is the most massive Terrestrial planet and the Moon is
about the least massive object) and
because these two objects are the two most well-studied Terrestrials.
How do we learn things
about the interiors of planets? This is an interesting question
because we do not probe the deep interiors of
planets directly, e.g., by drilling holes directly into them.
At most,mines reach a kilometer or two beneath
the surface of the Earth (the
radius of the Earth is over 6,000 kilometers). Most everything
we know has been learned through indirect means.
Probes of the Interiors of Planets
