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OCT. 2012

Pluto's Growing Family

promo image showing P5, Pluto's fifth moon

Pluto and its moons

P luto's family of moons just got larger. Astronomers discovered a new fifth moon circling the icy dwarf planet, located in the Kuiper Belt at the outskirts of our solar system.

The tiny new satellite — temporarily named P5 — was uncovered by NASA's Hubble Space Telescope during a search for rings around Pluto. Astronomers are hunting for both potential hazards and observing opportunities for NASA's New Horizons spacecraft, now heading to Pluto for a 2015 flyby. New Horizons will be the first spacecraft to visit the dwarf planet and study it in detail. Following that encounter, the spacecraft will study other objects in the Kuiper Belt.

The new moon is estimated to be irregular in shape and 6 to 15 miles (10 to 24 kilometers) across. By comparison, Charon, Pluto's largest moon, is 746 miles (1,200 kilometers) across. Two other moons, Nix and Hydra, range from 20 to 70 miles (32 to 113 kilometers) in diameter. The last of Pluto's known moons is P4, spotted in 2011, with an estimated diameter of 8 to 21 miles (13 to 34 kilometers). P5 appears to lie in the same plane as the other four moons.

Names from Greek mythology

The names for Pluto and its family of moons come from Greek mythology. Discovered in 1930, Pluto was named for the Greek god of the underworld, who was perhaps better known as Hades. The moon, Charon, discovered in 1978, was named for the ferryman who carried souls to the underworld. Nix, one of two moons discovered in 2006 with Hubble, is named for Nyx, the goddess of the night and Charon's mother. Hydra, the other moon spied in 2006, is named for the many-headed, serpent-like beast of ancient times.

It's a good bet Pluto's two newest moons, P4 and P5, will also bear the names of characters from Greek mythology. A few possible names are Erberus, Nyx's husband and Charon's father; Styx, the river that divided the living world from the underworld; Cerberus, Pluto's three-headed dog; and Hypnos or Thanatos, two sons of Nyx.

Astronomers will continue to monitor the Pluto system until New Horizons arrives. Maybe they will find another member of Pluto's family.


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