OBSERVATIONS OF THE LUNAR PLASMA WAKE FROM THE WIND SPACECRAFT ON DECEMBER 27, 1994

On December 27, 1994, the WIND spacecraft crossed the lunar wake at a distance of 6.5 lunar radii ( R(L) ) behind the moon. The observations made were the first employing modem instruments and a high data rate. The SWE plasma instrument on WIND observed new aspects of the interac tion between the solar wind and unmagnetized dielectric bodies. The pl asma density decreased exponentially from the periphery of the wake to wards its center as predicted by simple theory. Behind the moon two di stinct cold ion beams were observed refilling the lunar cavity. The io ns were accelerated along the direction of the magnetic field by an el ectric field of the order 2x10(-4) volts/m. The region of plasma deple tion was observed to extend beyond the light shadow, consistent with a rarefaction wave moving out from the wake into the undisturbed solar wind.