Pluto now has at least five moons. Can we go back to calling it a planet?

Long considered a planet, Pluto was reclassified as a 'dwarf planet' in 2006 by the International Astronomical Union. Will the discovery of a fifth moon prompt astronomers to reconsider?

|
NASA/ESA/M. Showalter (SETI Institute)
This image, taken by NASA's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5, as photographed by Hubble's Wide Field Camera 3 on Saturday.

Scientists on Wednesday (July 11) announced the discovery of a fifth moon orbiting Pluto in a major solar system find. But while many people think of moons as accessories for planets, like the Earth's moon or Jupiter's many moons, Pluto doesn't quite make the cut in the International Astronomical Union's (IAU) definition of "planet."

Despite of some determined lobbying by die-hard supporters to change its dwarf planet status, more moons around Pluto won't change its classification, experts say.

"Does it change the planetary status? Of course not," Michael Brown, an astronomer at the California Institute of Technology, wrote to SPACE.com in an email. Brown's discovery of Eris, a rocky object about the size of Pluto, was a major factor in the IAU's decision to reassess exactly what constitutes a planet.

The IAU ruled that to be called a planet, an object has to meet three conditions. It must orbit the sun without being another object's satellite, it must have enough gravity to make it sphere-shaped and it must clear the area around it of other objects. But even with Pluto's five moons, it doesn't "clear the neighborhood."

Six years after the IAU's ruling, some controversy still surrounds the decision, but the official ruling is unlikely to change in response to finding more Plutonian moons. [The Moons of Pluto Revealed (Photos)]

Pluto isn't the only dwarf planet that has moons. The dwarf planets Eris and Quaoar have one, while Haumea has at least two.

No one has found any other dwarf planet that has five moons, but that may be because scientists have studied Pluto more carefully than other dwarf planets, say both Brown and Alan Stern, a planetary scientist at the Southwest Research Institute in Boulder, Colo., and an advocate for classifying more objects as planets.

"It might turn out that Kuiper Belt planets commonly have significant numbers of moons," Stern told SPACE.com.

For Pluto, at least, the number of known moons may continue to grow in the near future. As scientists continue to scrutinize Pluto, looking for objects around it that may affect the New Horizons spacecraft that will arrive at Pluto in 2015, they may find even more moons.

The scientists responsible for finding out everything they can about Pluto before New Horizons' arrival have found that Pluto's moons are arranged in concentric circles around the dwarf planet. They've found moons located in what they call positions 1, 3, 4, 5 and 6.

"It makes you wonder if there's something at location 2 and locations 7, 8 and 9," said Mark Showalter, a planetary astronomer at the SETI Institute in Mountain View, Calif., who led the team that discovered Pluto's new moon.

Follow SPACE.com on Twitter @Spacedotcom. We're also on Facebook and Google+.

Copyright 2012 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Pluto now has at least five moons. Can we go back to calling it a planet?
Read this article in
https://www.csmonitor.com/Science/2012/0712/Pluto-now-has-at-least-five-moons.-Can-we-go-back-to-calling-it-a-planet
QR Code to Subscription page
Start your subscription today
https://www.csmonitor.com/subscribe