Want to name Pluto's two tiniest moons? Then you'll need to dig deep into mythology.

Astronomers announced a contest Monday to name the two itty-bitty moons of Pluto discovered over the past two years.

Three Pluto moons already have names associated with Hades and the underworld. They are Charon (KEHR-on), the ferryman of Hades; the half-human, Half-fish spirit Nix; and the multi-headed monster Hydra.

The two unnamed moons need similarly shady references. Right now, they go by the bland titles of P4 and P5. They're no more than 15 to 20 miles across.

Online voting will last two weeks. Twelve choices are available at the website "plutorocks." Choices include the hero who slew Hydra, Hercules; and Styx, the river to the underworld. Write-in suggestions are welcomed.