  The compositions of diverse planetary bodies are of fundamental interest to
planetary science, providing clues to the formation and evolutionary history of
the target bodies and the Solar system as a whole. Utilizing the X-ray
fluorescence unique to each atomic element, X-ray imaging spectroscopy is a
powerful diagnostic tool of the chemical and mineralogical compositions of
diverse planetary bodies. Until now the mass and volume of focusing X-ray
optics have been too large for resource-limited in-situ missions, so
near-target X-ray observations of planetary bodies have been limited to simple
collimator-type X-ray instruments.
  We introduce a new Miniature lightweight Wolter-I focusing X-ray Optics
(MiXO) using metal-ceramic hybrid X-ray mirrors based on electroformed nickel
replication and plasma thermal spray processes. MiXO can enable compact,
powerful imaging X-ray telescopes suitable for future planetary missions. We
illustrate the need for focusing X-ray optics in observing relatively small
planetary bodies such as asteroids and comet nuclei. We present a few example
configurations of MiXO telescopes and demonstrate their superior performance in
comparison to an alternative approach, micro-pore optics, which is being
employed for the first planetary focusing X-ray telescope, the Mercury Imaging
X-ray Spectrometer-T (MIXS-T) onboard Bepicolumbo. X-ray imaging spectroscopy
using MiXO will open a large new discovery space in planetary science and will
greatly enhance our understanding of the nature and origin of diverse planetary
bodies.
