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Fourth Moon discovered
around Pluto
Pluto and friends (Image: NASA/ESA/M. Showalter/SETI Institute)
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.
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.
Smashing time
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.
Team member Alan Stern of the Southwest Research Institute in Boulder,
Colorado, also heads the New Horizons mission that will fly by Pluto in
2015.
He is excited by the discovery but says it reinforces the need to keep
scanning the Pluto region for more objects that could pose a hazard to
New Horizons.
"We don't want our spacecraft running into any debris that's still hanging
around from the massive collision that spawned the formation of Pluto's
smaller satellites," he says.
around Pluto
Pluto and friends (Image: NASA/ESA/M. Showalter/SETI Institute)
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.
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.
Smashing time
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.
Team member Alan Stern of the Southwest Research Institute in Boulder,
Colorado, also heads the New Horizons mission that will fly by Pluto in
2015.
He is excited by the discovery but says it reinforces the need to keep
scanning the Pluto region for more objects that could pose a hazard to
New Horizons.
"We don't want our spacecraft running into any debris that's still hanging
around from the massive collision that spawned the formation of Pluto's
smaller satellites," he says.