Alan Boyle, in his wonderful Cosmic Log, has a great interview with the inimitable S. Alan Stern, lead scientist on the New Horizons space mission to Pluto. That’s Alan on the left, with his baby in the background. Pluto was a planet when New Horizons launched in January 2006, but it officially lost its planet status in August of that year after the International Astronomical Union voted in a new planet definition that left Pluto as a dwarf planet and now a plutoid.
Boyle’s interview with Stern comes on the heels of an IAU announcement on June 11, 2008 in Paris that objects like Pluto will henceforth be called plutoids. The suffix oid is often used in the sciences to mean something similar, not necessarily exact, to something else. The IAU says:
Plutoids are celestial bodies in orbit around the Sun at a semimajor axis 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. Satellites of plutoids are not plutoids themselves, even if they are massive enough that their shape is dictated by self-gravity. The two known and named plutoids are Pluto and Eris.
According to this definition, Pluto is similar, not necessary exact … to itself? If IAU scientists had training in language skills, maybe the strange case of Pluto wouldn’t be. But strange it is. According to the IAU’s definition, it’s Pluto’s failure to clear the neighborhood around its orbit that caused it to lose its planet status, and that still has S. Alan Stern steaming. 
For example, Alan said:
In fact, the IAU definition doesn’t come close to allowing Earth to be a planet …because of the near-Earth objects, the Earth is technically disqualified. But even if you could forgive that … and clear up the language, the issue is that as you go farther and farther away from the sun, the equations that describe the mass required to “clear a zone” show that the objects have to get more and more massive. So Mercury qualifies in Mercury’s orbit, but Mercury would not qualify in Earth’s orbit. Earth might qualify in its current orbit, but if we put the earth where Pluto is - in other words, if Pluto were the mass of the earth - it still wouldn’t qualify.
Food for thought. And to me the image immediately above and right says it all. That’s Pluto at the center of its own planetary system with its large moon and two known smaller moons. As Alan likes to say, if it looks like a dog and barks like a dog, it’s a dog … even if it’s a chihuahua.
Of course, Alan is just one passionate astronomer (and, don’t forget, lead scientist for the first space mission ever to explore Pluto, due to arrive in 2015), but he says other astronomers care as deeply about this issue as he does, and there’s no doubt the public cares. For our part, EarthSky ran a text and chart today focused on Pluto’s annual opposition - when it is opposite the sun from Earth - and viewers have already begun spontaneously commenting on Pluto’s lost planet status.
That’s because, even to us laypeople, the IAU’s decision still rankles. When the IAU took away Pluto’s planet status - thereby reducing the number of planets in our solar system from 9 to 8 - it effectively pulled in our solar system’s outer boundary as seen in the imaginations of most of us. Sure, the solar system is no different than it was before, but school children - and in fact most adults - won’t pick up on that subtlety. The IAU pulled our collective horizon in … and that’s not what astronomy is supposed to do.
What do you think? Should Pluto be re-instated as a planet?
Pluto Believe poster above copyright 2006 mythoslegends.com. Illustration by Pat Rawlings. Used with permission.
Pluto should never have been called a planet in the first place. It is not a planet, and if it was on a different path it would be nothing but a large comet. Irrational Pluto freaks need to get over it!!!
I suppose we should get over it. We could get over it if the IAU would clean up its definition … and grandfather in Pluto as a planet.
.
I side on Pluto being a planet. If it weren’t for mathematical predictions Pluto may not have been discovered. Probably would be the same for the other two planets discovered by mathematics then observation–Uranus and Neptune. More planets may be discovered as well as time goes on.
The current definitions (plutoid & dwarf planet) are inconsistent and not applied evenly to what the IAU currently considers to be plutoids & dwarf planets (OR even planets). They just don’t make sense. I believe the IAU has lost its credibility. Until they can stand up (remove the egg from their face) and admit their mistake, I think most scientists and lay people will feel the same. The IAU will not only lose the support of people all over the world, but they will also lose the very membership which made it a “once credible” organization.
Also, definitions are not based on the IAU’s determination of what “they” think definitions should be. Rather, definitions are decided by their usage. Collectively, if we don’t use these “new” definitions, then they really only exist in the minds of the IAU.
Siobhan, insightful comment. I always wondered who gave the IAU the right to determine ‘official’ names and categorizations for celestial bodies, anyway. I suspect they gave themselves that right.
Thanks for commenting,
Deborah
Thanks Deborah!
While I’m not a scientist (just an interested person) I’ve read the definitions put forth by the IAU. Regardless of who decides the new “definitions” to be added to dictionaries, another issue has been lost here…..and that’s “common sense”. If I (as a lay person) can read the definitions and know they don’t make sense, then there’s a problem with the definition.
Just because someone has risen to the ranks of scientist or holds a degree in some field, that degree- when handed over, does not include “common sense”. Either you have it, or you don’t. I suspect the IAU is lacking in this gene.
You know, I don’t know. I wonder. I don’t know if you followed the history on this, but an IAU committee had just recommended that Pluto stay a planet … and that Ceres and Eris both be made planets … so that we’d have more planets, not fewer. But - in the space of a few days - that idea was voted down and this new definition voted in. It all seemed very hasty at the time. I’m just not sure what happened.
A sad business.
Deborah
I do remember. Personally, I don’t have a problem with adding to the current 9 planets. I believe most people don’t- if the definition fits. But the current IAU definition should also exclude Earth, Jupiter, Neptune and Mars. And that’s fine with me too- if the definition fits. But only Pluto got the ax. If we go by the IAUs defintion we should only have 4 planets. Again, that’s O.K.- we’ll just call Earth a “Humanoid”…..a place where humans dwell.
-Siobhan
As I said in this post … I think it’s the role of astronomy in our culture to expand our horizons. More planets, yes! Fewer planets? It just seems wrong.
All this nomenclature is arbitrary anyway. These are just bodies in space, over which we’ve thrown our net of language. So there’s really no right or wrong here, and I suspect nature will always defy our attempts to establish clearcut definitions.
Referring to the IAU’s definition, let me just say this- it’s way to descriptive and exclusive. I say, LESS is MORE! Keep the definition simple enough to make sense and (why not) include MORE planets.
-Siobhan
That Pluto poster is the dorkiest thing you could tack on your wall.
Jay- just for clarification, are you referring to “dorkiest” in it’s usual definition OR the IAUs definition of “dorkiest”?
By the way, I love the poster!
Reynolds Observatory (Potsdam, NY) opened its doors to the public on June 27-28 for a night of stargazing. While looking upward, the conversation turned to Pluto. I was amazed at the deeply-felt comments from the kids (mostly middle school age). For the most part, they expressed profound disappointment with Pluto’s demotion from planethood, almost as if a loved family member had been booted from home.
Many of these kids had a firm knowledge of the solar system, proudly rattling off the names of the planets and dwarf planets (Mercury, Venus, Earth, Mars, Ceres - dwarf planet, Jupiter, Saturn, Uranus, Pluto - dwarf planet & Eris - dwarf planet). Much to my surprise, ALL of these kids thought Pluto had been demoted because it was too small or not massive enough to be a planet. But when I thought it over, doesn’t the term “dwarf planet” make this very implication?
If, indeed, we wish to come up with terminology that can be readily understood by intelligent school-aged children, I’m not so sure the term “dwarf planet” has adequately cleared the confusion zone!
Don’t blame it on the kids! I forgot to list Neptune between Uranus & Pluto!
What makes the least sense is the IAU’s determination that a dwarf planet is not a planet at all. That’s like saying a grizzly bear is not a bear! And it is inconsistent with the use of terminology in astronomy: dwarf stars are still considered stars, and dwarf galaxies are still considered galaxies. If the IAU or a newer group with more common sense reverses this one flawed, nonsensical statement and allows for dwarf planet to be a subclass of planet, much of this problem will be resolved.
Yes, the IAU gave themselves the authority to make these decisions, but they seriously bungled the job, with only four percent voting on the last day of a two-week General Assembly. In this digital age, no electronic voting was allowed, meaning anyone who couldn’t be in a room in Prague on August 24, 2006 had no say in the matter. Most who voted were not planetary scientists but other types of astronomers. And many planetary scientists are not even members of the IAU because they have long been turned off by the closed, byzantine manner in which the organization operates. So there is nothing to stop an alternate group from forming and deciding they want to do a better job at this.
Any planet, if it were on a “different path,” would have different properties. And any planet, even Jupiter, if brought close enough to its parent star, would outgas its atmosphere and develop a tail like a comet. This argument is nothing but a straw man.
What we have is a flawed process with an untenable defintion dictated by fiat by 424 individuals. Almost as many astronomers immediately responded with a petition describing the new definition demoting Pluto as sloppy and refused to use it. Why should anyone get over it? If something is wrong, it’s just as wrong two or ten or fifty years later as it was originally.
As we are discovering more and diverse planets in this and other solar systems, we should be broadening, not narrowing our definition of planet. I urge everyone to consider the best planet definition I’ve ever heard, which was given by my astronomy instructor, Al Witzgall. He said, “a planet is a non-self luminous spheroidal object in orbit around a star.” That’s it. Under that we can establish subcategories such as terrestrial planets, gas giants, ice giants, dwarf planets, hot Jupiters, super Earths, and likely more types yet to be discovered.
Pluto is a planet, as are Ceres, Eris, MakeMake, Sedna, and all the round KBOs. Facts cannot be changed by a vote. The IAU sham of 2006 should be reversed ASAP.
Oh, and Jay, I have that poster hanging on my wall, and I’m damn proud of it!