Dactyl Asteroid

Int

Moon of Asteroid Ida.

Astronomical specifications:

Discovery
Orbital characteristics:
Distance from Sun	km
Perihelion	(10⁶ km)
Aphelion	(10⁶ km)
Inclination	deg
Eccentricity
Orbital periode rond Sun	days
Main orbital speed	km/s
Inclination to Sun equator	deg
Number of moons
Rings
Physical characteristics:
Dimensions	km
Radius	km
Surface area	km²
Volume	10⁶ km³
Mass	10²⁴ kg
Density	g/cm³
Equatorial surface gravity	m/s²
Escape velocity	km/s
Rotation period	days
Surface temperature	K
Axial tilt	deg
Atmospheric composition

This image is the most detailed picture of Dactyl taken by the Galileo spacecraft's camera. The camera fortuitously captured the previously unknown moon at a range of about 3,900 kilometers, just over 4 minutes before the spacecraft's closest approach to Ida. More than a dozen craters larger than 80 meters in diameter are clearly evident, indicating that Dactyl has suffered numerous collisions from smaller solar system debris during its history. The larger crater on the terminator is about 300 meters across. At the time this picture was taken, Ida was about 90 kilometers away from the moon. (Courtesy NASA/JPL)

Descriptions:

Dactyl is the first natural satellite of an asteroid ever discovered and photographed. The tiny moon is about 1.2 by 1.4 by 1.6 km (0.75 by 0.87 by 1 mile) across. The name is derived from 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. Other mythological accounts say that the Dactyli were Ida's children by Zeus.
Dactyl is made more or less from the same kind of material as Ida. As an S-type asteroid, Ida is composed mostly of silicate rocks. Galileo scientists believe the moon may have been created at the same time as Ida when an older, larger asteroid was shattered in a collision with another asteroid, giving birth to dozens of smaller asteroids. Alternatively, it is possible that Ida was hit by a smaller object even more recently, leaving a crater on the asteroid and throwing off the material that became the small moon.
Galileo scientists also believe it is virtually impossible 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.

Mission details:

The greatest discovery from the Galileo fly-by was that Ida has a natural satellite. Although Galileo flew past Ida in August 1993, the discovery wasn't made until late in February 1994 when images stored on the spacecraft's tape recorder were finally transmitted to Earth. The moon has been named Dactyl by the International Astronomical Union.

Dactyl missions:

Name	Launch Date	Launch rocket	Weight (kg)	Mission
Galileo	18-Oct-1989	Shuttle STS-34		Galileo flew past Ida in August 1993, the discovery wasn't made until late in February 1994 when images stored on the spacecraft's tape recorder were finally transmitted to Earth.

Ref.: #91 - update: 30.03.11

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