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Ned Potter is the science correspondent for ABC's "World News with Charles Gibson." He has reported on such topics as space exploration, the human genome and climate change.
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'Plutoid'?
June 11, 2008 5:59 PM
Two years ago the International Astronomical Union did Pluto the indignity of demoting it from the list of planets in the solar system. Now it's rearranged the language.
For the last two years Pluto and other like bodies have been labeled "dwarf planets." Now, says the IAU, they'll be "Plutoids."
Plutoid...Plutoid? Roll it over on your tongue a little bit. "Plutoids," says the IAU, "are celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit." That's a long way of saying they're far, and big enough to be spheres, but not big enough that their gravity has drawn in other objects that may have passed nearby.
For now there are only two Plutoids -- Pluto, and Eris, a little world far beyond that was discovered in 2004.
Ceres, the largest of the asteroids between Mars and Jupiter, spent two years as a "dwarf planet," but it won't be a Plutoid. No doubt the Ceresians will be insulted.
There are reasons, astronomers have argued, for this bit of sophistry. The goal of science is to understand and categorize the universe, and new categories are needed as our understanding of the universe changes.
But...Plutoid?
(Above: Pluto with its three known moons, Charon, Hydra and Nix, which will presumably continue to be known as "moons.")
June 11, 2008 | Permalink | Share | User Comments (37)
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Why don't they just call them big rocks?
Posted by: mark | Jun 11, 2008 6:17:54 PM
Note from Ned--
Good thought, Mark--but if you were at the IAU you'd get an argument. Jupiter, Saturn, Uranus and Neptune aren't rocky. In space, nothing's simple.
Posted by: Ned Potter | Jun 11, 2008 6:24:25 PM
You write that "new categories are needed as our understanding of the universe changes" - well, this may have applied to the introduction of the "dwarf planet" category but certainly not to the new subcategory which will always include every dwarf planet except one and provides no extra insights.
The sole reason for this was another IAU vote two years ago that defined this subclass - with Pluto as its declared prototype - as a kind of consolation prize for the disgruntled Pluto fans.
Posted by: Daniel Fischer | Jun 11, 2008 6:36:28 PM
What's wrong with planetoid? or planetitse?
Posted by: cturple | Jun 11, 2008 7:51:54 PM
Personally, I prefer Altoids.
It is a curiously strong and refreshing term for celestial objects in our solar system that at least deserve MINTioning.
Posted by: Engineer270 | Jun 11, 2008 8:15:34 PM
One proposal back in 2006 was "planetino" - actually pretty clever, since the neutrino is much smaller than a neutron, shares some properties (i.e. no charge) and yet is a different beast and not just a small neutron. But this proposal never came up for vote.
Posted by: Daniel Fischer | Jun 11, 2008 10:23:37 PM
If we’re going to use technical terms than Charon, Hydra and Nix are not moons, but satellites. The term “moon” for those rocky things that orbit planets is colloquial, although certainly common in the scientific community. So Titan, Europa, Io, Phobos . . . all technically satellites, not moons.
Posted by: Hungry Donner | Jun 11, 2008 11:02:37 PM
cturple
Planetoids is what Ceres and its neighbors were called a long time ago. The notion that asteroids were pieces of planet, hence planetoids went out of favor. Surprise, its coming back!
Posted by: Quietman | Jun 12, 2008 12:43:35 AM
Eh? I don't mind 'dwarf planets'. Far better sounding than 'Plutoids'. The new name just sounds too wierd and make it seems Pluto and others are the size of asteroids when they are not.
Gee, change it back, will ya, IAU?
Posted by: GWP, Franklin Boro, NJ | Jun 12, 2008 7:29:48 AM
What's in a name? Well, apparently, a lot, since the scientific community is having such a difficult time with this whole episode in astronomy. Frankly, I find it quite amusing watching and listening to a crowd of supposedly educated and enlightened people struggling with this. And, it will all be finished up by political wrangling, rather than a scientific consensus. What's wrong with calling them 'lumps?'
Posted by: Andy | Jun 12, 2008 8:54:44 AM
our tax dolloars hard at work ;-)
Posted by: chuck | Jun 12, 2008 8:54:44 AM
Planetini?
Posted by: cturple | Jun 12, 2008 8:56:31 AM
Yet more anal-retentive dissection of information into the increasingly trivial. How will referring to these types of celestial bodies as "Plutoids" rather than "dwarf planets" change anything or deepen one's understanding of the subject? A rose by any other name...
Posted by: Publius | Jun 12, 2008 10:23:00 AM
cturple
Planetini?
cute!
Posted by: Quietman | Jun 12, 2008 1:41:54 PM
Planetchen?
Posted by: Rocko | Jun 12, 2008 1:52:04 PM
The ancient Greeks named them Planets a.k.a. wanderers. Since they can't have a say in this matter, the original name should stand. There is no good reason not to considers Ceres or Pluto or Eris as Planets. Clearing orbits is actually pretty meaningless more so when the orbit is so large and erratic. Dwarf Planet I can understand as its just another way to say it is a small planet, just like calling Jupiter a gas giant, it is what it is.
BTW while moons are satellites of planets, planets are satellites of stars. Moon is an english translation of the original greek and satellite has a broader meaning. So calling natural planetary satellites "moons" is more accurate, but technically (by the ancient definition) they are also planets.
Posted by: Quietman | Jun 12, 2008 1:54:08 PM
One word: planette
Posted by: Plutocrat | Jun 12, 2008 3:33:30 PM
To Chuck who says "our tax dolloars hard at work" I know your statement is meant to be tongue in cheek, but just an FYI...the IAU is an international organization of astronomers. It doesn't have much to do with American taxes.
At least we didn't pay for the stupid name. :)
Posted by: Joshua | Jun 12, 2008 5:17:17 PM
Pluto will always be a planet in my eyes.
Posted by: ellsbells930 | Jun 12, 2008 6:09:45 PM
Maybe it should be "Plutroid" the whole process has been a pain in the butt.
Gene
Posted by: Gene | Jun 12, 2008 6:11:24 PM
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