Among the five, the first three are lucky enough to have names. The first one (known since 1978) is called "Charon", a boatman of the dead in Greek mythology. The next two were found together, in 2005, and are called "Nix" (the mother of "Charon" and the goddess of night) and "Hydra" (the mythical nine-headed serpent).
The last two have the eminently boring identifiers of "S/2011 (134340) 1" and "S/2012 (134340) 1", denoting when they were found. "S/2012 (134340) 1" was located in July 2012.
What are these five?
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The satellites of Pluto, the dwarf-planet-formerly-known-as-a-planet. By the way, "Pluto" is the Roman God of the Underworld.
This day last year: Q.287