Cited research: Astron. Astrophys. 515, A98 (2010)

Planets seem to have no effect on the X-ray output of their parent stars, say Katja Poppenhaeger and her colleagues at the University of Hamburg in Germany.

Theorists have proposed that a planet's gravity could excite a star by causing it to bulge slightly or, similarly, that a planet's magnetic field could connect with that of its star and cause X-ray 'hotspots'. A previous study presented evidence for this effect.

Poppenhaeger et al. studied X-rays streaming from 72 nearby stars that host planets. In contrast to the earlier work, they find no obvious effect, and say that the phenomenon might appear in a few instances, for the most massive, close-in planets. E.H.