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113 Amalthea

An asteroid that circles the Sun in the main Asteroid Belt between the orbits of Mars and Jupiter. Amalthea is named for a being from Greek mythology, though the details of her story vary. In most versions, Amalthea was the she-goat who suckled the young Zeus as he hid from his father Chronos, a she-goat later immortalised among the stars as the constellation Capricornus. In other versions, Amalthea was a nymph, the keeper of the goat rather than the goat itself.

Amalthea is unusually dense of a minor planet of its comparatively small size (it has a diameter of less then fifty kilometres). The explanation is thought to lie in its physical similarity to the rather larger body known as Metis. These two asteroids are so close in composition that they seem to have shared an origin, as part of much larger minor planet that broke apart in the distant history of the Asteroid Belt. If this is correct, then Metis formed from the core of that ancient object, while smaller Amalthea had its origins in a fragment of the mantle flung out into space.

Amalthea shares another characteristic with Metis: each of these asteroids shares its name with one of the moons of Jupiter. The Jovian Amalthea is a small inner moon, though 'small' is relative here: though small for a member of Jupiter's system, Amalthea the moon is some four times the size of Amalthea the asteroid.


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