  Stellar variability induce by starspots can hamper the detection of
exoplanets and bias planet property estimations. These features can also be
used to study star-planet interactions as well as inferring properties from the
underlying stellar dynamo. However, typical techniques, such as ZDI, are not
possible for most host-stars. We present a robust method based on spot
modelling to map the surface of active star allowing us to statistically study
the effects and interactions of stellar magnetism with transiting exoplanets.
The method is applied to the active Kepler-9 star where we find small evidence
for a possible interaction between planet and stellar magnetosphere which leads
to a 2:1 resonance between the spot rotation and orbital period.
