Alas, poor Pluto - June 12, 2008
Pluto, demoted two years ago from a planet to a 'dwarf planet', has another moniker. Pluto, it seems, is now a 'plutoid'.
Yes, the International Astronomical Union is at it again. In an unexpected development (see comments), the IAU's executive committee has approved the term 'plutoid' for the following bodies: "Plutoids 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." Yeah, that. 
This all of course follows the outcry in 2006 (Nature story here, subscription required [Update: our blogging on the subject, though, is free to all...]) when the IAU kicked Pluto out from full-fledged planetary status. The newly designated plutoids include two objects currently: Pluto and the other big icy object that is known to orbit out there, called Eris. Ceres, which meets the criterion of size, doesn't qualify since it orbits in the asteroid belt. Got it?
Not all planetary scientists are thrilled. Alan Stern, NASA's former science chief who led the team that discovered two moons of Pluto, told the Associated Press: "It's just some people in a smoke-filled room who dreamed it up....Plutoids or hemorrhoids, whatever they call it. This is irrelevant." David Morrison of the NASA Ames Research Center told Space.com: "This seems like an unattractive term and an unnecessary one to me."
What do you think? Leave a comment below.
Image, of Pluto and its largest moon, Charon: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA
Comments
Nature's (the printed magazine's, that is) coverage of the events in Prague 2 years ago was pretty distorted in key aspects, and now your blog doesn't get it right either: the naming of a subcategory of dwarf planets is not at all "an unexpected development" but the result of a formal resolution passed at the IAU General Assembly back then!
As a kind of consolation prize for the disgruntled plutophiles there was a majority in favor of defining a subcategory of dwarf planets living in the Kuiper Belt, with Pluto as its prototype, but then there was no agreement on how to call these distant ice balls - "plutonian objects" was the proposal but it didn't pass.
Now the name for this subclass has finally been agreed on (by the responsible IAU parties), though I must agree with D. Morrison that it is unnecessary indeed: Since there is no possibility to discover another dwarf planet in the asteroid main belt, it will always be that plutoids = dwarf planets minus Ceres.
Posted by: Daniel Fischer | June 12, 2008 03:00 AM
Maybe those who have platonic affections with Pluto now understand the intricacies of the issue and humble down.
Posted by: Dr.Arvind Mishra | June 12, 2008 03:30 AM
Well, you need a name for everything. If "plutoids" had been rejected, people would have used periphrases like "Kuyper belt planets" or "dwarf planets with weird emo names" to refer to Eris and Pluto. Stern's reaction only strikes as resent.
Posted by: mokawi | June 12, 2008 03:43 AM
No-no;
All wrong... plutoids are actually the inhabitants of Pluto; while hemorrhoids are the inhabitants of Uranus
Posted by: bob | June 13, 2008 04:44 AM
Since there is no possibility to discover another dwarf planet in the asteroid main belt…
Why exactly is Vesta not considered a “dwarf planet”? It is “near spherical” in shape, most likely due to self-gravitation (surface gravity ∼1/6th that of the Moon), indeed Vesta melted and differentiated like the big boys following its formation. It seems crazy not to consider it a kind of planet (more so than Ceres, which as far as I know is not thought to have melted and differentiated).
Posted by: Michael McNeil | June 18, 2008 05:13 PM
The question with Vesta is whether it is mostly round because of the effects of self-gravity (hydrostatic equilibrium). My understanding is that most people think that that is probably the case, but until that's determined for sure (the Dawn mission, currently on its way to Ceres and Vesta, might be able to figure this out) Vesta remains a candidate dwarf planet. (But it still wouldn't be a plutoid, since it doesn't orbit beyond Neptune.)
Posted by: Alexandra Witze | June 18, 2008 05:23 PM
But it still wouldn't be a plutoid, since it doesn't orbit beyond Neptune.
Right. However, doesn't this imply that presently the other shoe is going to drop, and a new category 'Ceresoids' going to appear, to include Ceres, perhaps Vesta, and any other hydrostatically suspended worldlet (that may be found to be such) in the inner Solar System?
Posted by: Michael McNeil | June 18, 2008 06:30 PM
Could be. The one thing I am sure of is that this whole discussion will go on for quite some time....
Posted by: Alexandra Witze | June 18, 2008 06:34 PM
Stern is entirely justified in his reaction. While the initial demotion of Pluto was made by four percent of the IAU--no electronic voting was allowed--this latest decision was made by an even smaller number. Leading planetary astronomers had no idea this was in the works and were never informed until it was a done deal. The fact is, the IAU is using closed, archaic processes to reach these conclusions, and the processes are just as important as the conclusions themselves.
A large contingent of astronomers opposed the original demotion of Pluto, and 300 signed a petition led by Stern saying they will not use it. The IAU needs to come up with an inclusive process that seeks input from all in the field, including many planetary scientists who are not IAU members.
All this could be easily resolved by the IAU reversing its decision that dwarf planets are not planets at all (a determination that makes no linguistic sense) and establishing dwarf planets as a subclass of planets. Then we have no need for a term like Plutoids; we can simply distinguish Kuiper Belt dwarf planets from asteroid belt dwarf planets while still acknowledging all these objects, due to their being in a state of hydrostatic equilibrium fall under the broad category of planets.
Posted by: Laurel Kornfeld | June 24, 2008 04:56 PM
All this speculative rhetoric is unimportant to me. What should be of concern to most is the things we can learn about these planets and objects out in space. In science there is a lot of childish ego floating around and that's a shame and should not be. Learning should be co-operative open minded activity and not dictitorial. I for one am simply facinated by the data about the various things of the heavens and it's going to be a great day to see those photos come in on Pluto and her moon, no matter what anyone is calling it.
Posted by: Johann Kuester | August 9, 2008 08:31 PM