Geoscience Reference
In-Depth Information
Table 1.
Characteristics of Jupiter, Saturn, and Earth.
Parameter
Earth
Jupiter
Saturn
Distance from Sun (AU)
1
5.2
9.5
Equatorial radius (Earth = 1)
1
11.2
9.5
Rotation period (Earth = 1)
1
0.415
0.445
Inclination (
◦
)
23.5
3.1
26.7
Main atmospheric species
N
2
,O
2
,O
H
2
,H,He
H
2
,H,He
Magnetic field (G)
0.31
4.28
0.22
Magnetic moment (Earth = 1)
1
20,000
600
+11
.
3
◦
−
9
.
6
◦
−
0
.
0
◦
Dipole tilt wrt rotation axis
Magnetosphere size (
R
planet
)
6-12
R
E
50-100
R
J
16-22
R
S
10
3
-10
4
Auroral input power (Earth = 1)
1
10-100
Energy source(s)
Solar wind
Rotation
Solar wind +
rotation
Magnetospheric plasma source(s)
Ionosphere,
Io, Galilean
Satellites, rings,
solar wind
satellites
ionosphere
Notes:
1 AU (astronomical distance) = 1
.
496
×
10
13
cm, Earth equatorial radius (
R
E
)=
6
,
378 km. Average auroral input power at Earth
∼
1-100
×
10
9
W.
and Earth and Martian exospheres. Higher spatial and spectral resolution
information on planetary X-rays is improving our understanding on the
physics of the X-ray production on the planetary bodies, which are much
colder than traditional million-degree K or higher temperature plasmas in
the solar corona and astrophysical objects.
6
In this paper, we summarize the recent results of soft (
0.1-2.0 keV)
X-ray observations on Jupiter, Saturn, and Earth: all the three planets
having dense atmospheres and intrinsic magnetospheres, and known to emit
X-rays. Table 1 provides some of the characteristic parameters of these
planets. Reader are referred to other reviews for more details.
1
,
3
-
5
,
7
∼
2. Earth: Auroral Emissions
It is well known that the X-ray aurora on Earth is generated by ener-
getic electron bremsstrahlung,
8
-
10
and the X-ray spectrum of the aurora
has been very useful for studying the characteristics of energetic electron
precipitation.
9
,
11
-
15
The PIXIE X-ray imager on the Polar spacecraft mea-
sured X-rays in the range 2-60 keV.
16
The high apogee of the Polar satel-
lite (
∼
9
R
E
) enabled PIXIE to image the entire auroral oval (Fig. 1) with
