On October 29, 1991, the Galileo spacecraft flew by the asteroid Gaspra on its way to Jupiter.
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Gaspra was the first asteroid to ever be visited by a spacecraft. It orbits near the inner edge of the asteroid belt. The Galileo spacecraft had been travelling through the asteroid belt for about two months before it reached Gaspra. Galileo was 990 miles away from Gaspra when it whizzed by, and it was travelling at a relative speed of about 5 miles per second. The spacecraft took several photos of the asteroid and used an instrument called the Near-Infrared Mapping Spectrometer to study its chemical composition and other physical properties. Galileo determined that Gaspra has an irregular and elongated shape measuring about 12 miles long and 7 miles wide. The images revealed that Gaspra was also covered in craters. Because Galileo was too far away for Gaspra's gravity to affect it, the spacecraft was not able to determine the asteroid's mass.