X-RAY EMISSION FROM JUPITER, SATURN, AND EARTH: A SHORT REVIEW - Advances in Geosciences - page 227

Table 2. Characteristics of X-ray emissions of Jupiter, Saturn, and Earth.

Emitting Emitted Special Major production

power a Planet region characteristics mechanism

Earth Auroral 10-30 MW Correlated with Bremsstrahlung from

atmosphere magnetic storm and precipitating electrons

substorm activity

Non-auroral 40 MW Correlated with solar Scattering of solar

atmosphere X-ray flux X-rays

Jupiter Auroral 0.3-1 GW Pulsating ( ∼ 30-60 min) Ion precipitation (outer

atmosphere X-ray hot spot in magnetosphere and/or

north; in south emitted solar wind) + electron

from a band ∼ 180 ◦ bremsstrahlung

wide in longitude

Non-auroral 0.3-2 GW Relatively uniform Scattering of solar

atmosphere over the disk, X-rays + ring current ion

correlated with solar precipitation (?)

X-rays
Saturn Auroral and 0.1-0.4 GW Correlated with solar Scattering of solar
non-auroral X-ray flux X-rays + electron
atmosphere bremsstrahlung (?)
a The values quoted are “typical” values at the time of observation. X-rays from all
bodies are expected to vary with time. For comparison the total X-ray luminosity from
the Sun is 10 20 W.

It has been suggested that the upper atmospheres of the giant planets
Saturn and Jupiter act as “diffuse mirrors” that backscatter solar X-rays.
Thus, these planets might be used as potential remote-sensing tools to
monitor X-ray flaring on portions of the hemisphere of the Sun facing away
from near-Earth space weather satellites. 35 , 38 , 41
The X-ray aurora on Earth is generated by energetic electron
bremsstrahlung. 8 - 10 The auroral X-rays from Jupiter are produced by
charge-exchange of highly-ionized energetic heavy ions precipitating from
the outer magnetosphere and/or solar wind. 1 , 25 - 30 At higher energies
( > 2.0 keV) the auroral X-rays at Jupiter 31 could be produced by electron
bremsstrahlung process. However, at lower ( < 2.0 keV) energies electron

bremsstrahlung falls short by orders of magnitude in explaining the Jupiter
auroral X-ray flux. Also the spectrum shape at lower energies is inconsistent
with the bremsstrahlung shape (see Figs. 6 and 9). 26 , 37 At Saturn there is
no clear indication of an X-ray aurora. 40 , 41 X-ray aurora produced by elec-
tron bremsstrahlung is expected at Saturn, but it will probably be weak and
could escape detection by present-day instruments, because Saturn aurora
is relatively weaker than that on Jupiter (see Table 1), and Saturn does not

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