Titan and Venus are both unmagnetized bodies enveloped by induced magnetospheres created within the flowing plasmas in which they are embedded. When Saturn's magnetosphere extends beyond the position of Titan, as during the Voyager 1 flyby on November 12, 1980, the plasma incident at Titan contains a steady magnetic field approximately perpendicular to the plasma flow velocity. At Venus the incident plasma usually contains a time-varying magnetic field, but occasionally, the interplanetary conditions remain steady for the few hours required for the Pioneer Venus orbiter to pass through the induced magnetosphere. In particular, on February 28, 1979, the interplanetary field appears to have been stable and transverse to the solar wind velocity during the wake pass which was selected for a comparative Venus-Titan study. For both wakes, symmetry properties of the meaured magnetic fields were used to infer the directions of ambient plasma flow. In each case the flow direction differed from nominal, with the flow at Titan aberrated about 27¿ radially inward of the corotation direction and the flow at Venus aberrated about 10¿ relative to the heliocentric radial direction. Corroborating evidence for the aberrated flows was provided by plasma observations. The wake field magnitudes were nonuniform, and in both cases, reduced magnitudes were found on field lines linked to the illuminated (dayside) ionospheres. Finally, both induced magnetotails contained regions in which the projection of the magnetic field onto the incident magnetic field was negative. This observation may indicate that in an induced magnetosphere the plasma flows toward the mid-tail current sheet in the near wake, thus producing a field configuration that corresponds to a reconnection geometry. |