  We study the free boundary problem for contact discontinuities in ideal
compressible magnetohydrodynamics (MHD). They are characteristic
discontinuities with no flow across the discontinuity for which the pressure,
the magnetic field and the velocity are continuous whereas the density and the
entropy may have a jump. Under the Rayleigh-Taylor sign condition $[\partial
p/\partial N]<0$ on the jump of the normal derivative of the pressure satisfied
at each point of the unperturbed contact discontinuity, we prove the
well-posedness in Sobolev spaces of the linearized problem for 2D planar MHD
flows.
