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Pluto’s Five Moons

Postmillennialism —  Leave a comment

Pluto, the dwarf planet that was once considered the ninth planet, has a growing entourage of satellites.

On July 11, 2012, astronomers announced that a fifth moon had been discovered orbiting the dwarf planet. Researchers using NASA’s Hubble Space Telescope found the moon. The discovery comes almost exactly one year after Hubble spotted Pluto’s fourth moon, a tiny body currently called P4.

Pluto has one very large moon that is almost half the planet’s size. Discovered in 1978, it was named Charon after the demon who ferried souls to the underworld in Greek mythology. The huge size of Charon (648 miles or 1,043 km in diameter) sometimes leads scientists to refer to Pluto and Charon as a double dwarf planet or binary system. Pluto’s diameter is 1,430 miles (2,302 km).

Pluto and Charon are just 12,200 miles (19,640 km) apart, less than the distance by flight between London and Sydney. Charon’s orbit around Pluto takes 6.4 Earth days, and one Pluto rotation — a Pluto day — also takes 6.4 Earth days. This means Charon hovers over the same spot on Pluto’s surface, and the same side of Charon always faces Pluto, a phenomenon known as tidal locking.

While Pluto appears reddish, Charon seems grayish. Scientists suggest Pluto is covered with nitrogen and methane while Charon is covered with ordinary water ice.

Compared with most of solar system’s planets and moons, the Pluto-Charon system is tipped on its side in relation to the sun. Also, Pluto’s rotation is retrograde compared to the other worlds — it spins backwards, from east to west.

In 2005, as scientists photographed Pluto with the Hubble Space Telescope in preparation for the New Horizons mission — the first spacecraft to visit Pluto and the Kuiper Belt — they discovered two other tiny moons of Pluto, now dubbed Nix and Hydra. These are two to three times farther away from Pluto than Charon, and they are thought to be just 31 to 62 miles (50 to 100 kilometers) wide each.

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