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 manif
est 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.
Terrestrial exoplanets are on the verge of joining the ranks of astronomically accessible objects. Interpreting their observable characteristics, and informing decisions on instrument design and use, will hinge on the ability to model these planets s
uccessfully across a vast range of configurations and climate forcings. A hierarchical approach that addresses fundamental behaviors as well as more complex, specific, situations is crucial to this endeavor and is presented here. Incorporating Earth-centric knowledge, and continued cross-disciplinary work will be critical, but ultimately the astrophysical study of terrestrial exoplanets must be encouraged to develop as its own field.
