  While it may seem counterintuitive that X-ray astronomy should give any
insights into low-temperature planetary systems, planets orbit stars whose
magnetized surfaces divert a small fraction of the stellar energy into high
energy products: coronal UV and X-rays, flare X-rays and energetic particles,
and a high-velocity stellar wind. In our Solar System, X-ray emission gives
unique insights into the solar activity, planetary atmospheres, cometary comae,
charge exchange physics, and space weather across the Solar System. The stellar
activity of young stars is greatly elevated and can substantially affect
protoplanetary disks and planet formation processes. We highlight six studies
achievable with the planned International X-ray Observatory which address in
unique ways issues in planetary sciences: probing X-ray irradiation of
protoplanetary disks with the iron fluorescent line and its effects on disk
turbulence; study the complex charge-exchange X-ray emission from Jupiter and
the Martian exosphere; elucidate charge-exchange processes in cometary comae;
understanding heliospheric charge-exchange emission and the interpretation of
the soft X-ray background; and examining the magnetic activity of
planet-hosting stars and its evaporation of planetary atmospheres.
