Geoscience Reference
In-Depth Information
from Jovian inner radiation belts. Later it was suggested
34
that elastic
scattering of solar X-rays by atmospheric neutrals (H
2
) and fluorescent
scattering of carbon K-shell X-rays from CH
4
molecules located below the
Jovian homopause are also potential sources of disk X-rays.
XMM-Newton's 69 h of Jupiter observation, in November 2003, demon-
strated that day-to-day variation in disk X-rays of Jupiter are synchronized
with variation in the solar X-ray flux (Fig. 7), including a solar flare that
has a matching feature in the Jovian disk X-ray light curve.
35
The X-rays from the disk are quite uniformly distributed across the
low-latitudes (Fig. 8) — in contrast to the auroral X-rays. Auroral X-rays
from the north (60-75
◦
N latitude) are dominantly confined to
150-190
◦
longitude and those from the south (70-80
◦
S latitude) spread almost half-
way across the planet (
∼
300-360
◦
and 0-120
◦
longitude), while the disk
X-rays are quite uniformly distributed and are largely confined to
<
50
◦
latitude in both hemispheres.
36
The spectrum of X-rays from the disk is also
harder and extends to higher energies than the auroral spectrum (Fig. 9).
No periodicity has been observed in disk X-ray lightcurve.
26
,
36
,
37
Recent studies suggested that the X-ray emission from the Jovian disk
is largely due to scattered solar X-rays and that processes occurring on the
Sun control the X-rays from Jupiter's disk.
35
,
36
-
38
∼
6. Saturn
The X-ray emission from Saturn was unambiguously detected by XMM-
Newton in October 2002
39
and by Chandra in April 2003.
40
X-rays were
detected mainly from the low-latitude disk and no clear indication of auroral
X-rays was observed.
Recent observation of Saturn (Fig. 10) by Chandra in January 2004
showed that X-rays from Saturn are highly variable — a factor of 2-4 vari-
ability in brightness in a week's time.
41
In these observations an X-ray flare
has been detected from the non-auroral disk of Saturn, which is seen in
direct response to an M6-class flare emanating from a sunspot that was
clearly visible from both Saturn and Earth (Fig. 11). This is the first direct
evidence suggesting that Saturn's disk X-ray emission is principally con-
trolled by processes happening on the Sun.
41
Also a good correlation has
been observed between Saturn X-rays and F10.7 solar activity index. The
spectrum of X-rays from Saturn disk is very similar to that from the disk
of Jupiter (Fig. 12).
