Moon-solar wind interaction: First results from the WIND/3DP experiment

Launched on November 1, 1994, the WIND spacecraft passed behind the moon on December 27, 1994 and remained in its optical shadow for similar to 41 minutes. At the time the moon was immersed in the interplanetary medium and a large amount of new data has been collected by the WIND/3DP experiment. The nature of the flow near the moon is described by presenting detailed electron and ion plasma parameters in various regions; a structured lunar plasma umbra is clearly observed downstream of the moon at X(SSE) similar to -6 R(M), characterized by a gradual decrease of electron and ion densities to values of <0.5 cm(-3) near the center of the optical umbra. The plasma umbra is surrounded by a penumbra region in which plasma densities and magnetic field magnitude decrease and plasma flow undergoes small but noticeable variations. Analysis of magnetic shielding effects show that medium energy electrons follow the interplanetary magnetic field lines and are partially occulted by the moon. These first WIND results on the detailed properties of the downstream flow and the cavity extent are compared with fluid descriptions of the global moon-solar wind interaction.