Goals: While en route to its primary science mission at Jupiter, Galileo's mission team used two fortunate encounters with asteroids as bonus science opportunities and equipment tests for the Jupiter orbital mission.
Accomplishments:In 1991, Galileo passed the asteroid 951 Gaspra at a
distance of 1,600 kilometers (1,000 miles). Galileo found that Gaspra is an irregular object (19 by 12 by 11 kilometers), which lacks the large craters common on many planetary satellites.
In 1993, Galileo had crossed paths with asteroid 243 Ida, at a distance
of 2,400 kilometers (1,500 miles). Much to everyone's surprise, Galileo
images showed a tiny moon orbiting Ida - the first known moon of asteroid. Dactyl, about
1.5 kilometers in diameter, orbits about 100 kilometers (62 miles) from Ida's center.