Physical Characteristics
Ida's mass is between 3.65 and 4.99 × 1016 kg. Its gravitational field produces an acceleration of about 0.3 to 1.1 cm/s2 over its surface. This field is so weak that an astronaut standing on its surface could leap from one end of Ida to the other, and an object moving in excess of 20 m/s (70 ft/s) could escape the asteroid entirely.
Ida is a distinctly elongated asteroid, with an irregular surface, and is somewhat "croissant-shaped". Ida is 2.35 times as long as it is wide, and a "waist" separates it into two geologically dissimilar halves. This constricted shape is consistent with Ida being made of two large, solid components, with loose debris filling the gap between them. However, no such debris was seen in high resolution images captured by Galileo. Whilst there are a few steep slopes tilting up to about 50° on Ida, the slope generally does not exceed 35°. Ida's irregular shape is responsible for the asteroid's highly uneven gravitational field. The surface acceleration is lowest at the extremities because of their fast rotational speed. It is also low near the "waist" because the mass of the asteroid is concentrated in the two halves, away from this location.
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