Amalthea is the third moon from Jupiter
Galileo is thought to have discovered the largest four moons of Jupiter in 1610 with a small telescope. Galileo was unable to see the moon Amalthea because of its size. However, the moon is the third from Jupiter. It takes just under half an Earth day to move around the largest planet in the solar system.
Amalthea is thought to be an asteroid
The majority of moons are formed from debris in the area around a planet. However, Amalthea was not formed in this way. It is different in its characteristics when compared to the other, more than 60 moons of Jupiter. Amalthea is made of ice and porous materials and is thought to have formed far from the heat of Jupiter. Many astronomers theorize the moon was an asteroid that passed too close to Jupiter and was pulled in by its gravity.
Amalthea is a bright object
The moon of Jupiter is the reddest object yet discovered in the solar system and is thought to give off more heat and energy than it receives from the sun. The bright nature of the moon and Jupiter itself make it difficult for Amalthea to be photographed with most images being blurred and out of focus.
Not a spherical moon
When we think of a moon we usually believe them to be spherical or as close to a round shape as possible. As a former asteroid, this moon is not spherical being closer to a rectangle than any other shape. The moon has been measured at 145 miles wide, 91 miles wide, and 83 miles deep.
Amalthea does not spin in a traditional sense
Amalthea sits in an orbit 112,700 miles from Jupiter in the faint outer ring of the planet known as the Amalthea Gossamer Ring that has been created by a large amount of dust. The moon spins with the same side always facing Jupiter taking around 12 days to complete a single spin.
Moving through space can be a difficult thing for an asteroid and the many impacts Amalthea has received in and before arriving at Jupiter are easy to see. The surface of the former asteroid is covered in craters much larger than one would expect from an object of its size.
Discovered by an American astronomer
The largest four moons of Jupiter were discovered by the ancient Greek scientist, Galileo in 1610. American astronomer Edward Emerson Barnard discovered Amalthea on September 9th, 1892 and was the fifth moon to be discovered. Originally known as Jupiter V, this was the last moon to be discovered using a traditional telescope. Later moons were found using photographs and digital images.
The name comes from an ancient myth
Upon discovering Amalthea, Edward Emerson Barnard gave the moon its roman numeral name, Jupiter V. It was later christened Amalthea by the French astronomer Camille Flammarion and was only officially granted in 1976. In ancient Greek mythology, Amalthea was a nymph who cared for the infant Zeus by providing goat’s milk.
Moonlets are thought to orbit Amalthea
The close proximity to the surface of Jupiter makes it difficult for the moon to be fully explored by astronomers. This is because of the bright nature of the planet. When the Galileo orbiter made its way to Jupiter, the moon was observed in detail for the first time with a series of flashes captured by what was known as a star scanner. These nine flashes are thought to be moonlets orbiting Amalthea. These could take any size from small stones to much larger and require more exploration by space agencies.
Amalthea has a limited lifespan
Some astronomers believe Amalthea will eventually be destroyed by Jupiter because of how closely it orbits the planet. The tidal forces from Jupiter are thought to place a great strain on the moon. This will eventually result in the moon decaying. Once the decay takes place, the moon will fall into the surface of Jupiter and be destroyed.