Metis, Adrastea, Amalthea, and Thebe

     Four Jovian moons are very close to the mother planet. The closest is Metis, followed by Adrastea, Amalthea, and Thebe. They all have fairly circular orbits, and the planes of their orbits are close to the plane of the equator of Jupiter. They move swiftly around their mother planet in a counterclockwise direction. Metis completes three circuits before a single day passes here on earth, and the other three satellites are almost as fast.

     All four moons are small. According to NASA, Amalthea is the largest of the four with a mean radius of 83.45 km, while Adrastea is the smallest with a mean radius of only 8.2 km.

Discovery

     Since Amalthea is the largest, it is not surprising that it was the first to be discovered. Edward Emerson Bernard spotted it in 1892.

     The others remained unknown to science until they were detected on photographs taken by Voyager 1 and Voyager 2 in 1979. Stephen Synnott detected Metis and Thebe on photographs taken by Voyager 1, and Adrastea was detected by Jewitt and Danielson on photographs taken by Voyager 2.

Origin of Satellite Names

     Since Jupiter is the Roman equivalent of the Greek god Zeus, the moons of Jupiter are named after figures associated with Zeus in Greek mythology.

     Metis was the first wife of Zeus, according to Hesiod. Fearing that the children born to her would overthrow their father, Zeus swallowed her. Their child Athene saw the light of day anyway. She emerged from the head of Zeus. However, Metis remained in his belly. Since the Greek word “metis” means “wisdom” or “cunning,” the ancient Greeks believed that Zeus acquired wisdom by swallowing his wife.

     Adrastea and Amalthea are figures associated with the infancy of Zeus. Zeus was in danger of being swallowed by his father Cronus, so his mother Rhea found a hiding place for him on the island of Crete. Adrastea and her sister Ida were nymphs that took care of the baby Zeus. They fed him with milk of a goat named Amalthea. (This story occurs in an ancient text called Pseudo-Apollodorus. According to other versions, Amalthea is not a goat, but a nymph.)

     Thebe was a naiad who gave her name to the ancient Greek city of Thebes. Another Thebe gave her name to the ancient Egyptian city of Thebes. According to NASA, both consorted with Zeus. This does not seem to be in accord with mainline Greek mythology.

Physical Features

     A few physical features of these moons have received official names approved by the International Astronomical Union. According to the Gazetteer of Planetary Nomenclature, Thebe has a crater 40 kilometers in diameter. Its name is Zethus Crater. Zethus was the husband of Thebe, according to one version of the myth.

     Amalthea has two small craters: Gaea Crater and Pan Crater. Gaea is mother earth. It was her counsel that saved Zeus from being swallowed, according to Hesiod. Pan is a god with goat-like features.

     Amalthea also has two bright spots called faculae: Ida Facula and Lyctos Facula. Both are place names connected with the childhood of Zeus. Lyktos is the locality in Crete where his mother hid him, and Ida is a Cretan mountain in the area.

References

NASA: Jupiter – Moons 

http://solarsystem.nasa.gov/planets/profile.cfm?Display=Moons&Object=Jupiter

Gazetteer of Planetary Nomenclature: Zethus

http://planetarynames.wr.usgs.gov/Feature/6726?__fsk=965430456

Gazetteer of Planetary Nomenclature: Amalthea

http://planetarynames.wr.usgs.gov/SearchResults?target=AMALTHEA

Wikipedia: Adrastea

http://en.wikipedia.org/wiki/Adrasteia

Theoi: Amalthea

http://www.theoi.com/Ther/AixAmaltheia.html

“Theogony” by Hesiod; M.L. West, translator