Dactyl
The first satellite of an asteroid to be
discovered. Dactyl was found in orbit around Ida
by the Galileo probe when it flew by the
asteroid in 1993. The little moon, measuring 1.6 × 1.4 × 1.2 km,
was about 100 km from its much larger companion when photographed. Interestingly,
the spectra of Ida (an S-class
asteroid) and Dactyl reveal that the compositions of the two objects, though
similar, are not identical; Dactyl is not simply a bit of Ida that broke
off. Instead, it is thought that the binary system may have formed during
the collision and breakup that created the Koronis
family of asteroids. What seems certain is that the moon is a captured
object – something created completely separately from Ida that happened
to wander near the asteroid and be caught by its gravitational field. According
to the laws of celestial mechanics, such an event would deflect the smaller
object, but it would not be captured into orbit unless a third force of
some kind slowed it down.
It is named after the Dactyli, a group of mythological beings who lived
on Mount Ida. The Dactyli protected the infant Zeus after the nymph Ida
hid and raised the god on the mountain.
Related category
• NOTABLE
ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS
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