(243) Ida I Dactyl ( ) is a tiny

asteroid moon A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. , there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons (and binary objects, in general) are important ...

(1.6 km in diameter) that

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

243 Ida Ida, minor planet designation 243 Ida, is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. ...

. It was imaged by the ''

Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...

'' spacecraft on

August 28 Events Pre-1600 * 475 – The Roman general Orestes forces western Roman Emperor Julius Nepos to flee his capital city, Ravenna. * 489 – Theodoric, king of the Ostrogoths, defeats Odoacer at the Battle of Isonzo, forcing his way ...

, 1993; Dactyl was discovered while examining the delayed image downloads from Galileo on

February 17 Events Pre-1600 * 1370 – Northern Crusades: Grand Duchy of Lithuania and the Teutonic Knights meet in the Battle of Rudau. * 1411 – Following the successful campaigns during the Ottoman Interregnum, Musa Çelebi, one of the sons ...

1994 File:1994 Events Collage.png, From left, clockwise: The 1994 Winter Olympics are held in Lillehammer, Norway; The Kaiser Permanente building after the 1994 Northridge earthquake; A model of the MS Estonia, which sank in the Baltic Sea; Nels ...

. It was provisionally designated S/1993 (243) 1. The satellite was named after the

mythical Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narrati ...

creatures called dactyls who lived on

Mount Ida In Greek mythology, two sacred mountains are called Mount Ida, the "Mountain of the Goddess": Mount Ida (Crete), Mount Ida in Crete, and Mount Ida (Turkey), Mount Ida in the ancient Troad region of western Anatolia (in modern-day Turkey), which wa ...

according to

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities o ...

. Dactyl orbits Ida with a period of 1.54 days at an average distance of 108 km, with an inclination of 9° to Ida's

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

. The origins of Dactyl are unclear, but two main hypotheses exist. The first is that Dactyl and Ida formed at the same time, and the second is that Dactyl was knocked loose by a later impact. Dactyl was the first

discovered. Its discovery settled the long debate over the existence of asteroid moons.

External links

243 Ida and Dactyl
from ''The Nine Planets''

from ''Views of the Solar System''

announcing Dactyl's discovery

announcing Dactyl's naming
Ida and Dactyl
in false coloring, to reveal surface differences

References

{{Solar System moons (compact) Asteroid satellites Minor planets visited by spacecraft

See also

External links

References