This composite image shows the asteroid 243 Ida as seen from the Galileo
spacecraft during its approach on August 28, 1993. The six views were
shuttered through the camera's green filter and show Ida's rotation over a
period of about 3 hours 18 minutes. The asteroid makes a complete rotation
every 4 hours 38 minutes; therefore, this set of images spans about 3/4 of Ida's
rotation period and shows most of Ida's surface. By combining the
information in these views with that from the highest resolution images
returned from the spacecraft in September 1993, the size and shape of this
irregular body can now be determined accurately The asteroid appears to be
about 58 kilometers (36 miles) long and about 23 kilometers wide, with a very
irregular shape and volume of some 16,000 cubic kilometers. The images are
arranged in chronological order from a time 3 hours 51 minutes before closest
approach (upper left), through upper right, middle left, middle right lower left
and lower right (33 minutes before closest approach). The six images show ida
at the same scale throughout. Ida's rotation axis is roughly vertical in these
images, and the rotation causes the right-hand end of Ida to move toward the
viewer as time progresses. The first image was taken from a range of about
171,000 km (106,000 miles) and provides an inage resolution of about 1,700
meters per pixel (the highest resolution achieved for Ida is about 25 meters per
pixel). The second, taken 70 minutes later, is fromOn 119,000 kilometers,
followed by 102,000 kilometers, 85,000 kilometers, 50,000 kilometers, and
25,000 kilometers. The features on Ida are less sharp in the earlier views
because of the greater distances. Prominent in the middle three views is a deep
depression across the short axis of the Asteroid. This feature tends to support
the idea that Ida may have originally been formed from two or more separate
large objects that collided softly and stuck together. Also visible in the lower
left view is an apparent linear albedo or reflectance boundary. Color images
yet to be returned from the Galileo spacecrart may help resolve the question
of whether or not the two ends of Ida are made of different materials.
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