Mirror mode waves at Comet Halley

High resolution VEGA magnetic field and plasma data in Halley's magnetosphere reveal out-of-phase oscillations of the type expected to be driven by the mirror mode instability. The spacecraft passes through these structures in about 20 s. The magnetic energy density drops about 6.5 x 15 exp 9 ergs/cu cm in a typical event. The thickness of these regions is about a water-group ion gyro diameter. While such enhancements should be invisible against the comet when viewed perpendicular to the wavefronts, they could be visible as rays when viewed tangential to the wavefronts.