  A wide variety of solar system bodies are now known to radiate in the soft
x-ray energy (<5 keV) regime. These include planets (Earth, Jupiter, Venus,
Saturn, Mars): bodies having thick atmospheres, with or without intrinsic
magnetic field; planetary satellites (Moon, Io, Europa, Ganymede): bodies with
thin or no atmospheres; and comets and the Io plasma torus: bodies having
extended tenuous atmospheres. Several different mechanisms have been proposed
to explain the generation of soft x-rays from these objects, whereas in the
hard x-ray energy range (>10 keV) x-rays result mainly from the electron
bremsstrahlung process. In this paper we present a brief review of the x-ray
observations on each of the planetary bodies and discuss their characteristics
and proposed source mechanisms.
