Short answers, pulled from the story.
Galileo flew past 243 Ida on the 28th of August 1993, traveling at 12,400 m/s relative to the asteroid. The spacecraft came within 2,390 km of Ida during its closest approach and captured images of about 95 percent of the asteroid's surface.
243 Ida was discovered by Austrian astronomer Johann Palisa at Vienna Observatory on the 29th of September 1884. It was his 45th asteroid discovery, and it was later named by Viennese brewer and amateur astronomer Moriz von Kuffner after a nymph from Greek mythology.
Dactyl was discovered by Galileo mission member Ann Harch on the 17th of February 1994, while she was examining delayed image downloads from the spacecraft. Galileo had captured 47 images of Dactyl during its August 1993 flyby, but transmission delays meant the images were not reviewed until months later.
Dactyl is only 1.4 km in diameter, approximately one-twentieth the size of 243 Ida. It orbits Ida in the prograde direction, inclined about 8 degrees to Ida's equator, and was observed about 90 km from Ida during the Galileo flyby.
243 Ida is an S-type asteroid, classified based on its reflectance spectra. Galileo detected the silicate minerals olivine and pyroxene on its surface. Its bulk density of 2.27-3.10 g/cm3 is consistent with a composition similar to ordinary chondrite meteorites, with a porosity estimated at 11-42 percent.
The flyby provided evidence linking S-type asteroids, the most common type in the inner asteroid belt, to ordinary chondrite meteorites, the most common type found on Earth's surface. Space weathering was found to alter the surface spectra of S-types over time, explaining why remote telescopic observations had not matched ordinary chondrite spectra before the flyby.