From New Scientist:
Fourth moon discovered around Pluto
Updated 18:10 20 July 2011 by David Shiga
The cosmos loves irony. Five years after Pluto was stripped of its planet status, astronomers have discovered yet another moon in orbit around it, bringing its entourage to four.
The tiny body may have been born in the same collision that gave birth to Pluto’s other moons.
The Hubble Space Telescope spotted the new moon, which has been designated P4 for the time being. Astronomers estimate it is between 13 and 34 kilometres across. “I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles [5 billion kilometres],” says Mark Showalter of the SETI Institute in Mountain View, California, who led the observing team.
Three other moons of Pluto were already known. Charon, discovered in 1978, is by far the largest at about 1000 kilometres across. Nix and Hydra, discovered in Hubble images in 2005, are tiny by comparison: both are estimated to be between 32 and 113 kilometres in diameter.
All four moons are thought to have formed at the same time. “The discovery of this moon reinforces the idea that the Pluto system was formed during a massive collision 4.6 billion years ago,” says discovery team member Hal Weaver of Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.
“A big impact produced Charon, and the remaining three [moons] formed from the debris scattered further out,” Showalter told New Scientist.
Also from New Scientist:
What should Pluto’s new moon be named?
22:19 20 July 2011
David Shiga, reporter
Pluto’s tiny new moon needs a real name.
Right now astronomers are using two boring designators for it – P4 and S/2011 P1.
Ironically, the body tasked with approving an official name for the new moon is the same one that stripped Pluto of its planet status in 2006 – the International Astronomical Union (IAU).
The standard procedure is that the discovery team proposes a name to the IAU, which can either accept it or reject it and ask the team for more ideas.
By tradition, names of solar system objects are drawn from mythology. It has usually been Greek or Roman mythology, but more recently, astronomers have been drawing names from other cultures, too.
For example, one icy denizen of the Kuiper belt beyond Neptune is named Quaoar, after a creation god of the Native American Tongva tribe.
Pluto itself is named after the Roman god of the underworld, based on a suggestion made in 1930 by Venetia Burney of Oxford, England, who was 11 years old at the time.
The names of Pluto’s three previously discovered moons have so far continued that theme. The largest moon, Charon, is named after an underworld character in Roman mythology who ferried the dead across the river Styx.
In light of the discovery of a fourth moon orbiting Pluto, Mark Thompson ponders what it takes to be called a “planet”: here.
3 Small, Icy Worlds Discovered in Pluto’s Territory: here.
The (non-planet) Pluto could hide an ocean beneath its icy shell: here.
The controversy over Pluto’s status as a planet continues: here.
Linked solar eruptions explained: here.
Astronomers discover 50 new planets: here.
The Herschel Space Observatory has identified a twisted ring of dust and gas at the centre of the Milky Way galaxy. Parts of the ring have been seen before but this is the first time it has been observed as a whole: here.