The p and the l in Pluto's name stand for Perceval Lowell, the astronomer who long ago spearheaded the search for Pluto.
Nix and Hydra
Nyx is the Greek goddess of darkness and the mother of the underworld ferryman Charon, which is the name of Pluto's largest moon.
Hydra was a nine-headed monster that guarded the underworld. Its nine heads make it a particularly good companion for the ninth planet, Stern says.
Originally, the astronomers proposed "Nyx" as the name for the first moon, but the IAU rejected that spelling because it had already been used to name a small asteroid.
Still, Stern is very pleased with the official name.
"[The IAU] maintained everything we wanted, except they had to change a vowel," he said.
"My joke is that the IAU nixed 'Nyx,'" Stern said.
Much about the small moons remains a mystery. Nobody is sure how large the moons are. They could be tiny and bright or larger and dimmer.
What is known is that they are considerably smaller than Charon and travel well outside its orbit.
"They're somewhere between 30 and 100 miles [48 and 160 kilometers] in diameter," Stern said.
As for New Horizons, "[it's] halfway to Jupiter," Stern said.
The probe is due to arrive at Pluto on July 14, 2015.
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