  Jupiter, Saturn, and Earth - the three planets having dense atmosphere and a
well developed magnetosphere - are known to emit X-rays. Recently, Chandra
X-ray Observatory has observed X-rays from these planets, and XMM-Newton has
observed them from Jupiter and Saturn. These observations have provided
improved morphological, temporal, and spectral characteristics of X-rays from
these planets. Both auroral and non-auroral (low-latitude) 'disk' X-ray
emissions have been observed on Earth and Jupiter. X-rays have been detected
from Saturn's disk, but no convincing evidence for X-ray aurora on Saturn has
been observed. The non-auroral disk X-ray emissions from Jupiter, Saturn, and
Earth, are mostly produced due to scattering of solar X-rays. X-ray aurora on
Earth is mainly generated via bremsstrahlung from precipitating electrons and
on Jupiter via charge exchange of highlyionized energetic heavy ions
precipitating into the polar atmosphere. Recent unpublished work suggests that
at higher (>2 keV) energies electron bremsstrahlung also plays a role in
Jupiter's X-ray aurora. This paper summarizes the recent results of X-ray
observations on Jupiter, Saturn, and Earth mainly in the soft energy (~0.1-2.0
keV) band and provides a comparative overview.
