  Spinning planetesimals in a gaseous protoplanetary disk may experience a
hydrodynamical force perpendicular to their relative velocities. We examine the
effect this force has on the dynamics of these objects using analytical
arguments based on a simple laminar disk model and numerical integrations of
the equations of motion for individual grains. We focus in particular on
meter-sized boulders traditionally expected to spiral in to the central star in
as little as 100 years from 1 A.U. We find that there are plausible scenarios
in which this force extends the lifetime of these solids in the disk by a
factor of several. More importantly the velocities induced by the Magnus force
can prevent the formation of planetesimals via gravitational instability in the
inner disk if the size of the dust particles is larger than of order 10 cm. We
find that the fastest growing linear modes of the streaming instability may
still grow despite the diffusive effect of the Magnus force, but it remains to
be seen how the Magnus force will alter the non-linear evolution of these
instabilities.
