Ida and Dactyl: Asteroid and Moon.

This asteroid has a moon. The robot spacecraft Galileo on route to Jupiter in 1993 encountered and photographed two asteroids during its long interplanetary voyage. The second minor planet it photographed, 243 Ida , was unexpectedly discovered to have a moon. The tiny moon, Dactyl , is only about 1.6 kilometers across and seen as a small dot on the right of the sharpened featured image . In contrast, the potato-shaped Ida is much larger, measuring about 60 kilometers long and 25 km wide. Dactyl is the first moon of an asteroid ever discovered -- now many asteroids are known to have moons . The names Ida and Dactyl are from Greek mythology .