The flyby of Ida, a somewhat larger asteroid whose mean radius is
roughly 25 km, took place at 16:52:10 UT on August 28, 1993.
Closest approach at a distance of 2400 km was once again slightly
downstream of the asteroid. The data were stored on the spacecraft
until Galileo returned to Earth several months later. Would a
solar wind signature be present once again? The answer proved to
be affirmative. Abrupt IMF field rotations had occurred near the
asteroid. Strangely, the first perturbations occurred 
6
minutes before closest approach at a location substantially sunward
of the asteroid. Despite the improbable geometry of a wake-like
structure that extends upstream of its source in the flowing
plasma, it has been possible to demonstrate that the timing is
completely consistent with the predictions of plasma physics.
Because whistler waves speeds can exceed the typical solar wind
speed, the whistler-mediated interaction can provide perturbations
upstream of their source in a cone of angles extending from the
asteroid and generally aligned with the IMF direction. For Ida,
the IMF was at 
45
to the Ida-sun line, pointing towards
Galileo's trajectory, so the onset occurred at a position quite
consistent with an asteroid-imposed perturbation of the solar wind.
Work is in progress to determine if the perturbation again implies
that the source region extends beyond the asteroid itself.
Preliminary results suggest that it does and if this analysis holds
up, Galileo will have identified a second asteroid magnetosphere.