The discoverers of Pluto's fourth and fifth moons are letting Internet users have a say in what they should be named, by throwing the question open for a non-binding advisory vote.
The "Pluto Rocks" project, organized by the SETI Institute, is part of a trend pointing toward getting the public involved in the outer-space naming process. NASA, for example, has solicited name suggestions for the asteroid due to be visited by the OSIRIS-REx probe, and for one of the modules on the International Space Station (more on that later).
This time, the objects to be named are two tiny satellites of Pluto that were found during a detailed analysis of data from the Hubble Space Telescope: P4, which was discovered in 2011; and P5, detected just last year. The moons are only 15 to 20 miles (20 to 30 kilometers) across, at the limit of Hubble's observing power. The astronomers behind the discoveries were checking out Pluto's surroundings just to make sure the way was clear for NASA's New Horizons probe to fly past the dwarf planet in 2015.
Convention dictates that the discoverers of celestial bodies get to suggest names for adoption by the International Astronomical Union. When P4 and P5 were revealed, "I received literally hundreds of suggestions," said one of the leaders of the discovery teams, Mark Showalter, an astronomer at the SETI Institute's Carl Sagan Center for the Study of Life in the Universe.
Showalter has been involved in the naming of moons before (Saturn's Pan, as well as Uranus' Mab and Cupid), but that was nothing compared with the clamor over P4 and P5. "It seems that the public has a much greater interest in Pluto," he said.
He said it was Alan Stern, the principal investigator for the $700 million New Horizons mission, who suggested putting the name question up for a public vote. "I just jumped on it when he suggested it," Showalter said.
The ballot on the Pluto Rocks website offers 12 potential names for perusal, all of which follow the precedent that Pluto and its moons are named after Greek or Roman mythological figures with a connection to the underworld. Pluto, for example, was master of the underworld. Charon, Pluto's largest moon, is named after the boatsman that ferried the souls of the dead across the River Styx. The moons Nix and Hydra, discovered in 2005, were named after the goddess of the night and a many-headed monster that guarded one of the entrances to the underworld.
The 12 suggested names for P4 and P5 are Acheron, Alecto, Cerberus, Erebus, Eurydice, Heracles, Hypnos, Lethe, Obol, Orpheus, Persephone and Styx. Some of these names have already been used for asteroids, and in those cases, the teams might go for variant spellings just to avoid any confusion (for example, Orfeus instead of Orpheus, or Kerberos instead of Cerberus). Write-in votes are also allowed, and some of those write-ins might end up being added to the official ballot.
The voting deadline is Feb. 25. After the vote, the discovery teams will choose two names to submit to the IAU, and announce which names won out after their formal approval — most likely by April or so. "We're not going to guarantee that they'll be the top two names [in the voting], but they'll probably be high on the list," Showalter said. "We're not going to all this trouble just to pick names that we chose already."
Showalter and his colleagues want to retain some control just to make sure that they don't get railroaded by a media-driven ballot-stuffing campaign, such as the one that marked NASA's "name-the-module" contest in 2009. Back then, talk-show comedian Stephen Colbert drummed up more than 200,000 write-in votes to get a space station module named after himself. The space agency ended up calling the module Tranquility instead, but named the treadmill inside the module "C.O.L.B.E.R.T." as a consolation prize.
There could be similar shenanigans this time around, especially in light of Pluto's pop-culture popularity. "I suspect Minnie and Mickey will be high on the list of write-ins," Showalter joked.
The moon-naming contest could reignite the years-long controversy over the IAU's classification of Pluto as a "dwarf planet" rather than an honest-to-goodness planet — but Showalter said the labels don't matter all that much to him. "It's a very small planet, and it seems to me appropriate, based on its size, to call it a dwarf planet," he said. "I don't see that as a demotion."
Could Pluto have even more moons? That's the big reason why the discovery teams took so long to address the naming of P4 and P5. "Frankly, we wanted to wait until we scoured the data," just in case there was a sixth moon to add to the list, Stern said. But after months of scrutinizing the Hubble data, the astronomers concluded that the next discoveries would have to come from the New Horizons probe.
"Come 2015, I wouldn't be at all surprised if we have a P6, P7 and P8 to deal with," Showalter said.