Geology Reference
In-Depth Information
Table 1.1.
Basic data for planets
Orbit semi-
major axis
Escape
velocity
(km/s)
Revolution
period (yr)
Diameter
(km)
Rotation
(days)
Mass
(10
24
kg)
Density
(g/cm
3
)
(10
6
km)
(AU)
a
Name
Surface
Atmosphere
Mercury
57.9
0.39
0.24
4,879
58.65
0.33
5.4
4.3
Silicates
Trace Na
243.0 (R
b
)
Venus
108
0.72
0.62
12,104
4.87
5.2
10
Basalt,
granite?
90 bar: 97%
CO
2
Earth
150
1.00
1.00
12,756
1.00
5.97
5.5
11
Basalt,
granite,
water
1 bar: 78%
N
2
, 21%O
2
Mars
228
1.52
1.88
6,794
1.03
0.64
3.9
5.0
Basalt, clays,
ice
0.07 bar: 95%
CO
2
Jupiter
778
5.20
11.86
142,984
0.41
1,899
1.3
60
None
H
2
, He, CH
4
,
NH
3
, etc.
Saturn
1427
9.54
29.46
120,536
0.44
569
0.7
35
None
H
2
, He, CH
4
,
NH
3
, etc.
0.72 (R
b
)
Uranus
2871
19.19
84.02
51,118
86.8
1.3
21
None (?)
H
2
, He, CH
4
,
NH
3
, etc.
Neptune
4498
30.07 164.79
49,528
0.67
102
1.8
24
None (?)
H
2
, He, CH
4
,
NH
3
, etc.
Pluto
5906
39.48 247.9
2,302
6.39 (R)
0.013
2
1.3
CH
4
, ice
Trace CH
4
a
1AU (astronomical unit) = Earth
Sun distance, or ~149.6 × 10
6
km.
-
b
R = retrograde.
the Solar System outside the Sun. Jupiter and Saturn are
composed mostly of hydrogen and helium, while Uranus
and Neptune are composed mostly of water, ices, and
other volatile materials. Collectively, the giant planets
and Pluto are called the outer planets, referring to their
location in the Solar System.
The early history of the giant planets is similar to that of
the terrestrial planets. The giant planets also formed by the
accretion of smaller bodies, with each forming a nucleus
large enough to capture the lighter elements that had
escaped from the inner Solar System to the outer frigid
parts of the Solar System. As this process continued, the
giant planets grew to their large sizes, with heavier ele-
ments sinking to their interior. Most models of the giant
planets suggest that each contains a rock-like core, some
of which are larger than Mars.
Each of the giant planets resembles the Sun in compo-
sition, but not even the largest, Jupiter, was destined to
grow to a size suf
cient to initiate nuclear fusion.
However, giant planets do resemble the Sun in one impor-
tant way
Figure 1.2. The heavily cratered surface of the Moon, shown in
this view obtained by the Apollo 13 astronauts, represents the
first 0.5 Ga of the Solar
System. The dark, smooth area is Mare Moscoviense on the lunar
far side (NASA 70
final stages of planetary accretion in the
-
H
-
700).
The presence of large impact craters on the terrestrial
planets (
Fig. 1.2
) shows that their crusts had cooled and
solidi
ed in the
first 0.5 Ga of Solar System history before
all of the miscellaneous debris had been swept up.
each grew and evolved to have a family of
smaller bodies in orbit about them so that each resembles
the Solar System in miniature.
Although the giant planets have no
“
geology
”
because
they lack solid surfaces, their satellites are of great interest
for planetary geomorphology (
Table 1.2
). Collectively,
-
1.1.2 The giant planets
Jupiter, Saturn, Uranus, and Neptune are referred to as
giant planets. Relative to the terrestrial planets, these
planets are enormous and contain most of the mass in
