The concern is not necessarily that New Horizons, which launched in 2006, will slam into a Pluto moon that has thus far eluded detection.

MSN: New Pluto moon hints at perilous journey for spacecraft

Sometimes they need a little help from something like the Hubble Space Telescope, but its our peepers that ultimately spotted Pluto's fifth moon, P5.

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Charon, Pluto's largest moon, is named after the ferryman who carried the souls of the newly deceased across the River Styx, which divided the world of the living from that of the dead.

MSN: Hell of a Choice: Cerberus Leads for New Pluto Moon Name

The discovery of another moon around Pluto is exciting news for planetary science, but it's also likely causing some anxiety for the team in charge of New Horizons, a spacecraft set to be the first probe ever to visit the dwarf planet.

MSN: New Pluto moon hints at perilous journey for spacecraft

And water would be all the more exciting on Ganymede because it is the largest moon in the solar system (larger even than the planets Mercury and Pluto) and, like earth, it has a permanent magnetic field that protects part of its surface from bombardment by certain sorts of life-destroying radiation.

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P5 brings Pluto's known satellite tally to five, and it comes just a year after Hubble spotted moon number four, the similarly diminutive P4.

MSN: New Pluto moon hints at perilous journey for spacecraft