  We present a global MHD simulation of a turbulent accretion disc interacting
with a protoplanet of 5 Jupiter masses. The disc model had H/r=0.1,and a value
of the Shakura & Sunyaev alpha ~ 0.005. The protoplanet opened a gap in the
disc, with the interaction leading to inward migration on the expected time
scale. Spiral waves were launched by the protoplanet and although they were
diffused and dissipated through interaction with the turbulence, they produced
an outward angular momentum flow which compensated for a reduced flux
associated with the turbulence, so maintaining the gap. When compared with
laminar disc models with the same estimated alpha, the gap was found to be
deeper and wider indicating that the turbulent disc behaved as if it possessed
a smaller alpha. This may arise for two reasons. First, the turbulence does not
provide a source of constantly acting friction in the near vicinity of the
planet that leads to steady mass flow into the gap region. Instead the
turbulence is characterised by large fluctuations in the radial velocity, and
time averaging over significant time scales is required to recover the
underlying mass flow through the disc. Near the planet the disc material
experiences high amplitude perturbations on time scales that are short relative
to the time scale required for averaging. The disc response is thus likely to
be altered relative to a Navier--Stokes model. Second, the simulation indicates
that an ordered magnetic connection between the inner and outer disc can occur
enabling angular momentum to flow out across the gap, helping to maintain it
independently of the protoplanet's tide. This type of effect may assist gap
formation for smaller mass protoplanets which otherwise would not be able to
maintain them.
