  The excitation of precursor solitons ahead of a rapidly moving object in a
fluid, a spectacular phenomenon in hydrodynamics that has often been observed
ahead of moving ships, has surprisingly not been investigated in plasmas where
the fluid model holds good for low frequency excitations such as ion acoustic
waves. In this paper we report the first experimental observation of precursor
solitons in a flowing dusty plasma. The nonlinear solitary dust acoustic waves
(DAWs) are excited by a supersonic mass flow of the dust particles over an
electrostatic potential hill. In a frame where the fluid is stationary and the
hill is moving the solitons propagate in the upstream direction as precursors
while wake structures consisting of linear DAWs are seen to propagate in the
downstream region. A theoretical explanation of these excitations based on the
forced Korteweg-deVries model equation is provided and their practical
implications in situations involving a charged object moving in a plasma are
discussed.
