 If the giant and the primary were close enough for the magnetic fields to be linked, the orbit of the planet would wrap the field lines until the configuration became unstable followed by a violent release of energy in the form of a flare.Kepler discovered a number of closely orbiting gas giants, known as hot Jupiters; studies of two such systems showed periodic variations of the chromospheric activity of the primary synchronised to the period of the companion.Not all planetary transits can be detected by Kepler, since the planetary orbit may be out of the line of sight to Earth.