Significant magnetic field perturbations in the solar wind were observed during the Phobos-2 elliptical orbits around Mars when the spacecraft crossed the Phobos orbit. As remarkable feature, these so-called Phobos events were detected in all cases only on the upstream side of the Phobos orbit. A simple one-dimensional fluid model is developed which shows that a thin charged dust cloud with an extension of no more than 100 km is able to produce phase-standing, right-hand polarized precursor waves with a spatial periodicity of about the proton skin length. This is the same type of upstream waves which is generated by oblique, subcritical shocks. The measured period of the magnetic variations (≈40 s) may be explained as Doppler shift owing to the spacecraft motion through the standing wave structure. The fluid results are confirmed by hybrid code simulations. In conclusion, we suggest the Phobos events to be precursor waves resulting from the interaction of the solar wind with charged dust rings along the Phobos orbit. ¿ American Geophysical Union 1993