  A small percentage of normal stars harbor giant planets that orbit within a
few tenths of an astronomical unit. At such distances the potential exists for
significant tidal and magnetic field interaction resulting in energy
dissipation that may manifest as changes within the stellar corona. We examine
the X-ray emission of stars hosting planets and find a positive correlation
between X-ray luminosity and the projected mass of the most closely orbiting
exoplanets. We investigate possible systematics and observational biases that
could mimic or confuse this correlation but find no strong evidence for any,
especially for planets more massive than ~0.1 MJ. Luminosities and upper limits
are consistent with the interpretation that there is a lower floor to stellar
X-ray emission dependent on close-in planetary mass. Under the hypothesis that
this is a consequence of planet-star magnetic field interaction, and energy
dissipation, we estimate a possible field strength increase between planets of
1 and 10 MJ of a factor ~8. Intriguingly, this is consistent with recent
geodynamo scaling law predictions. The high-energy photon emission of
planet-star systems may therefore provide unique access to the detailed
magnetic, and hence geodynamic, properties of exoplanets.
