  Recent discoveries of strongly misaligned transiting exoplanets pose a
challenge to the established planet formation theory which assumes planetary
systems to form and evolve in isolation. However, the fact that the majority of
stars actually do form in star clusters raises the question how isolated
forming planetary systems really are. Besides radiative and tidal forces the
presence of dense gas aggregates in star-forming regions are potential sources
for perturbations to protoplanetary discs or systems. Here we show that
subsequent capture of gas from large extended accretion envelopes onto a
passing star with a typical circumstellar disc can tilt the disc plane to
retrograde orientation, naturally explaining the formation of strongly inclined
planetary systems. Furthermore, the inner disc regions may become denser, and
thus more prone to speedy coagulation and planet formation. Pre-existing
planetary systems are compressed by gas inflows leading to a natural occurrence
of close-in misaligned hot Jupiters and short-period eccentric planets. The
likelihood of such events mainly depends on the gas content of the cluster and
is thus expected to be highest in the youngest star clusters.
