One of many articles regarding the upcoming conference...

Experts meet to decide Pluto fate

IMHO pluto is NOT a planet....

Just thought i'd kick off the inevitable debate

I'm going to start a campaign to remove the planetary status of Mercury, if they drop Pluto. It's a glorified Vulcanoid!

If we kick out Mercury, then we ought to do the same to Mars: it's closer in size/mass to Mercury than it is to Venus or the Earth, and its proximity to the main asteroid belt suggests that it should be considered merely a largish inner asteroid...

Ok, Jupiter is a failed sub brown dwarf...

Nick

You can think of all sorts of ways of branding when something is or isnt a 'planet'...but two things come to mind.

Does it actually matter? If we say Pluto is a planet or not, Pluto is still Pluto. Why waste the time, money and effort discusing this matter at all?

Whatever constraints you attempt to bring on the classification of a 'Planet' at some point you will have to make an arbritrary cut off point of size, shape and location and under various headings of planet, planetoid etc etc define ranges for each of these.


Doug

"About 3,000 astronomers and scientists are meeting in Prague to determine the fate of Pluto and the relevance of millions of schoolbooks and encyclopaedias around the world."
_________

Much ado about nothing ~ I think they're just going to Prague for a big party.




IMHO Pluto should remain a planet for historical sake if nothing else.

Concerning Pluto and the planet definition debate:

We have the same issues in biology. For example genus, species and every other taxonomic rank are, in the last analysis, arbitrary. And, yes, there are young hotshot biologists who want to scrap these categories entirely as being unscientific - and just go with cladograms (phylogenetic trees) when referring to and defining plants. But the result of such a proposal would be chaos in terms of how professionals would need to refer to plants (would a forester bother to describe an elm as the second distal branch on the third proximal Magnoliid clade, for example?). And I don’t even want to imagine how amateurs and schoolchildren would cope under such as system.

Same thing with “planets”. The concept is an arbitrary one, but ancient and culturally important and useful in maintaining interest and support for astronomy and space exploration. This is not a negligible consideration.

My solution (and the one I’m hoping comes out of the IAU meeting this week): Grandfather Pluto in as a planet. And any future discoveries (such as Xena) that are at least as large as Pluto (in diameter or mass, take your pick) become planets, too. Yes, we may ultimately have 2 or 20 more planets in the solar system, but won’t that be fun and create public interest and the impetus for more exploration?

[...]

JRehling, that's one of the most sensible arguments I've heard in this eternal discussion :-)

I agree that the divisions are arbitrary, that the term planet is "cultural" (or historical) rather than scientific, and I would also suggest that -- as we learn more about extrasolar systems -- classificatory systems that make sense in terms of our own solar system may be useless when discussing other systems.

However, in practical terms, the IAU as a nomenclatorial body has dug itself into its own ditch by having one set of naming conventions for "major planets" and another set for "minor planets" and TNOs: without ever stating what the distinction was. The fatal result of this imprecision is that the IAU was forced to make a determination on where the boundary between major and minor planets was as soon as an object larger than Pluto was discovered.

It would be helpful if the IAU would stress the limits of the decision that they are going to make: not that they are going to define what a planet is for all time, but that they are clarifying, for their own purposes, what the word "planet" means in terms of their rules of nomenclature, and that they cannot rule on how the word "planet" might be used in other circumstances.

David brought up a good point that this is more procedural for the IAU than really anything else. Personally, I still feel that this argument over what is and what is not a planet is perhaps one of the most moronic arguments I have ever heard of. As others have mentioned, "planet" has no real scientific use.

I say let it be any natural object primarily (in other words not another planet, like Titan) orbiting a star. Yes, we have billions of planets. Do you have to memorize them all? Of course not. Since the voyagers flew past the giant planets, we have found moons that are just as interesting scientifically, if not more so. Can anyone here argue that Mercury is more scientifically important than Titan, Enceladus, Io, or Europa? But yet, because Mercury is given the gilded status of "planet" far more people are aware of Mercury and maybe a few of its properties, than they are aware of Titan or Io or any of the other interesting moons in our solar system.

And why are people having such a problem with Pluto being a planet or "Xena"? People can't contemplate a solar system with *shock* 10 planets? Did people in 1783 try to come up with definitions for planet to exclude Uranus? I mean 6 is a perfect number, there can't be more planets than the 6 known ones, obviously. So anything found outside the orbit of Saturn is a Trans-Saturnian object and not a planet, regardless of size. No, they accepted uranus as a planet, and its discovery spured on the hunt for another. Then Neptune's discovery spured the hunt for yet another.

If people want a size limiting definition, fine, go with the one rogelio suggested. Pluto is the lower limit for a planet. Anything found that is larger than it, is a planet. If there are 20 more planets, so be it. If there are thousands of potential planets, so be it. I'm not going to lose any sleep over it.

Yes, as volcanopele and others have mentioned, "'planet' has no real scientific use"

Yet... pure "science" is not completely the point here... It's possible that NH would not now be on its way to Pluto if there hadn't been that famous "Pluto - Not Explored" stamp in the planet postage stamp series.

Money, money for space exploration could be at stake. To me its seems appropriate and worthwhile for the IAU to decide the planet question. It's ivorytoweritis to deny the significance of the power of names and categories in influencing events that occur in the real world (like funding for space missions or astronomy research). The Pluto question has gotten a lot of play all over the world, and it does seem as if laypeople want a reasonable answer.

An interesting point. Would NASA have been able to fund a probe to Pluto, if it had been downgraded in status?

I think if they are wise, the ITU will create a sensible definition for "planet" and then agree on a grandfather clause to keep Pluto. The debate is moronic, and it will probably turn ugly if they downgrade it.

In the news ...

[quote name='volcanopele' date='Aug 14 2006, 06:47 PM' post='64281']
David brought up a good point that this is more procedural for the IAU than really anything else. Personally, I still feel that this argument over what is and what is not a planet is perhaps one of the most moronic arguments I have ever heard of. As others have mentioned, "planet" has no real scientific use.


I must say that I disagree. As reductionists, it is our job to categorize. Finding a workable definition
for a planet has only become necessary, and painful, because we have made so many fundamental
discoveries in our solar system and others since 1992 (the year the first KBO and the
first pulsar planets were detected). It's not about culture. It's about good science.

-Alan

It's also worth mentioning that Ceres used to be called a planet, but once it became clear how many other bodies were in the asteroid belt, it lost that status. (Be interesting to learn exactly how that happened; I suspect there wasn't any kind of formal vote.)

Besides, there's a nice symmetry in having eight planets and two asteroid belts. The four terrestrial planets are inside the original asteroid belt and the four jovian planets are between that asteroid belt and the Kuiper belt.

Just tell the public they're not losing a planet -- they're gaining a new asteroid belt. I think most people aren't even aware there's a Kuiper belt at all.

According to SpaceToday.net via NPR (National Public Radio):

A working group is expected to recommend to the International Astronomical Union (IAU) that Pluto be retained as a planet, opening the door for other solar system objects to also be designated as planets.

NPR reported this week that the group will likely report at an IAU meeting later this month in Prague that Pluto retain its designation as a planet, and that a new class of planets, perhaps called "dwarf planets", be created.

That class of planets would include Pluto, possibly the largest asteroids, and a number of the new large objects discovered in the outer solar system.

Pluto's classification as a planet has been questioned for the last several years as large icy bodies in the Kuiper Belt and beyond have been found. At least one of those objects, nicknamed Xena, is now believed to be larger that Pluto.

http://www.spacetoday.net/Summary/3452

I would like Pluto to remain a planet.

Does anyone feel like setting up a poll on this? (Idon't know how to.) There seem to be three positions:
1 The IAU should declare Pluto a planet.
2 The IAU should declare Pluto is not a planet.
3 The term 'planet' is scientifically obsolete and the IAU has no competence to decide on matters of wider word usage.
I go with number 3.

But we also shouldn't present the solar system as a neat and tidy place when it isn't. The discoveries since 1992 have allowed us to appreciate the complexity of not just our solar system, but other solar systems as well. From other solar systems, we have found large planets that don't following neat and tidy orbits, some have high eccentricities for example. We have found stars with two accretion disks at different inclinations. In our own solar system, we have found icy dwarf bodies that follow a miriad of orbits and have various shapes, and there maybe some the approach the size of the terrestrial planets.

The solar system (and other systems) are not neat and tidy places and we shouldn't pretend that it is. Listen, I understand we need a system for categorization. It allows us to more easily make sense of our world or the worlds around us. I understand that. But the amount of press this has gotten and the amount of breath and time spent on this is not worth it. Pluto is still Pluto whether it is a planet or a TNO, or any icy dwarf, or a dog.

Setting arbitrary definitions also makes the word less useful for scientific purposes. A TNO at 4000 km probably didn't form fundimentally any different from a 2000 km wide body (or a 1900 km wide body). As long as we make it clear to the public what the words value is (for classification purposes and for nomenclature purposes), I think we can come to an understanding. But if we treat it as if objects that are planets are some exclusive group or club and those that are just moons or minor planets are inferior and aren't worth our time in terms of exploration purposes (just because they are not planets), then we have a problem.

Okay, I'm sorry about the rant...

Jason, I think you and everyone else are missing Alan's point. No one is trying to obscure the fact that our "solar system [isn't] a neat and tidy place." Quite the contrary. Taxonomies and classification systems are very useful in science, especially in astronomy. Discerning hierarchical relationships, ipso facto, can lead to scientific discoveries.

You're right, there wasn't. The following historical summary discusses how it happened:
When Did the Asteroids Become Minor Planets?
The decision was in the hands of the compilers of astronomical almanacs. For the first 50 years after the discovery of Ceres, asteroids were listed together with the planets, between Mars and Jupiter, in order by length of their semi-major axes. In 1841 the British Nautical Almanac and Astronomical Ephemeris began to collectively name the four then-discovered asteroids as "Minor Planets". In 1851 asteroids 5-15 and Neptune were moved "to the back of the book" of the Berliner Astronomisches Jahrbuch. At the same time, numbers were substituted for the astronomical symbols that had been invented for them. In 1867, Ceres, Pallas, Juno and Vesta went "to the back of the book" as well. Likewise, in 1868, the Paris Observatory began to classify these four asteroids as "petites planètes". So for a few decades, at least, there were three categories of planet: major (Mercury-Neptune), minor (asteroids 5+) and a nameless middle group consisting of asteroids 1-4. In the '50s and '60s other almanacs also stopped printing the ephemerides of the asteroids in the same section with the planets or abandoned them altogether.

The distinct treatment of Ceres, Pallas, Juno and Vesta depended not so much on their size (though Ceres, Pallas, and Juno were drastically overestimated) but, I think, on the fact that they had been treated as planets for forty or fifty years -- in a situation comparable to that of Pluto today. They were, you might say, "grandfathered in". Astraea and the others were (c. 1850) newcomers, only discovered in the past decade, and so not worthy of the same degree of reverence!

If Pluto, 2003UB313 and some others are granted a middling status like "mesoplanet", perhaps we can expect them also to drift into being merely "minor planets" some decades from now.

I understand that. I guess my point was that given the current proposals (with the exception of the roundness one) are arbitrary and don't use anything fundamental about the body itself to seperate "minor" from "major". Based how much this is argued and how much press this gets, you'd think that this was something more important, but really, it isn't. Discerning hierarchical relationships is very important, I grant you, but most of the proposals don't do that.

Personally, I prefer a definition that is inclusive rather than exclusive. As the article by Tom Gehrels stated, such an inclusive defintion (which would be one that would allow for the discovery of "planets" in the Kuiper Belt, rather than excluding all members of that region of the solar system), would help to spur future scientific discoveries and would help boost research into the outer reaches of the solar system.

I don't disagree; but if it were the business of the IAU to try to make its nomenclatorial system conform to any one of several possible planetary taxonomies, surely the first order of that business would be to find a way of pointing out that Jupiter and Mercury are not the same kind of object?

Perhaps these will help some who have not seen them; sorry for spamming those who did-- the
links will save me from typing my views:

Gravity Rules: http://www.spacedaily.com/news/outerplanets-04b.html

Copernicus Smiled: http://www.thespacereview.com/article/450/1

I'm quite fond of the "rounded by gravity" criterion myself; but the presence of objects like 2003 EL61 and Iapetus makes it rather difficult to apply. Objects with diameters between 400km and 1600km exhibit a wide variety of shapes: spheres, near-spheres, flattened spheroids, spindly spheroids, nicely rounded ellipsoids, bumpy, lumpy, and partially concave ellipsoids, and plain old irregulars. If there's a direct correlation between shape and size or mass, it's not an obvious one.

Why wouldn't a cutoff above 1600km diameter be just as defensible a gravity-based division as one below 400km?

Careful, careful, careful! The roundness argument is not about whether an object is round or not-- because it could for axample be tidally bulgded or rotationally distorted. I's about whether its massive enough **Tto be rounded by gravity** in the absence of
the other effects. You will see this speccifically noted in the IAU language tomorrow.

-Alan

ps. EL61 is probably not a big egg: it's most likely a huge contact binary. At least that's where my money is.

I realize that there is this "out", but it seems to me that it makes the concept very nebulous and subject to a lot of special pleading. One might argue for any number of objects below 400km diameter, right down to the size of "roundable" water droplets, that they could be gravitationally rounded in some ideal situation, but due to a variety of other factors (like impacts) they don't happen to have fully realized their inner roundness. That's the argument used for Vesta, for instance: it would be a nice clean spheroid if it weren't for that rotten polar impact crater!



Interesting thought.

And for the sake of amusement, the author of a "liveblog" from Prague announces that:

Let's discuss this tomorrow after you see what the IAU position is. Some of your questions will be addressed.

-Alan

Ah, an intergalactic snob from the old days of astronomy. You know, the further it
is from the Sol system (meaning Percival Lowell and his ancient Martians with their
darn canals), the more important it is - to the professional astronomers.



Instead of this elitist attitude, I hope astronomers will use this opportunity to
educate the public and media on our favorite science while at least one aspect
of the field is hot, trendy, and generating publicity.

As for naming Pluto and all the smaller worlds, what about the good old term
Planetoid?

It means "little planets", is less awkward than dwarf planets, and goes in
line with the less accurate term asteroid (little star).

I also think black holes should be called collapsars, keeping in line with
pulsars and quasars.

[...]

What many people who have a sentimental attachment to the term "planet" lose sight of is the fact that the term originated in ancient times to describe the appearance of certain "wandering stars." There was absolutely no scientific need for it. Therefore, despite the very long usage of "planet" and what it has come to stand for, I don't have any particular qualms about redefining it, for example, to take into account our rapidly growing base of knowledge about Edgeworth-Kuiper Belt objects. And hey, if Alan Stern et al. ever find the hypothesized population of Vulcanoids, then I have no sentimental attachment in reclassifying Mercury, as well.

So does that mean that as a major comet brightens on approach to the sun, it magically transmogrifies into a planet? There has to be more to the definition than that.

David

Obviously they mean the absolute visual magnitude of the body itself, not any associated coma or other debris cloud.

I think that the concept of "planet" has really nothing to do with the scientific hierarchical classification system. As far as that goes, I think we have five major classifications -- ISSRO's (Inner Solar System Rocky Objects), GGO's (Gas Giant Objects), IGO's (Ice Giant Objects), KBO's (Kuiper Belt Objects) and OCO's (Oort Cloud Objects). A separate set of classifications can be applied to moons of these objects.

I will restate, though, that when an average citizen of the Earth asks "What are the planets?" he/she is asking something similar to "What's the layout and population of my town?" They don't want to gain new scientific insights into the Solar System, they want a number and a set of names they can wrap their minds around, feel comfortable with, and go out armed with the knowledge that they at least know the basic layout of their own little corner of the Universe.

For example, there was a time when the population of a town was only expressed in the number of adult white males that lived there. Then women and minorities made it clear that they needed to be counted, and so the concept of what made up the census of people in a given place changed. What we're arguing about here is similar to the little old lady who complains that the census says she lives alone, when she actually lives with her fourteen cats, and she demands that the cats be counted in...

In other words, your average person, in my humble opinion, doesn't care about the fine scientific distinctions. They want to know the names of the streets in their neighborhood, the names of the families that live nearby, and where City Hall, the grocery store and the shopping mall are located. They don't want (or need) to have their "naming of things" stretched out to include detailed numeric representations of every street, path, walkway, sidewalk, and alley, nor do they have any need to know the names of every cat, dog, gerbil and flea that lives near them. If you give them such a detailed accounting, they will simply ignore it. They will know it exists, but they just won't care.

I think that's why this whole issue with Pluto is getting some people energized. They don't really care why something is named a planet or some other thing, they want to know the equivalent of the street names in their town and where their friends and acquaintances live. They want to know the names of, and a little about, the "places" in our Solar System, and if that list grows from 9 to 256,347, they're going to ask for (and get!) a list of just those places they ought to consider "important."

In the end, it's that list they ask for -- the one that defines the "important" places in the solar system -- that will be the list of the "planets." At least, it will be the only list that anyone beyond a small handful of scientists will ever memorize or feel that they "know"...

-the other Doug

It has been announced on the SpaceDaily website that the committee was unanimous in defining a "Planet" as a body big enough to round itself off gravitationally, and whose shape is determined by hydrostatic rather than rigid forces.

Pluto remains a planet under this definition.

All seven members of the committee are reported to be in complete agreement on this. And this will be the draft submitted to the IAU.

They report that there are twelve known planets in our solar system under this definition.

Spacedaily claims that Charon makes the cut as a planet. I don't see how, since the body has to be in orbit around a star. It seems like they are saying that if the barycenter is outside either body (or something like that) then both bodies are planets.

Seems kinda silly to me. Worst. Definition. Ever.

? only 12? In your other post, you stated that they considered this size to be around 850 km. So in addition to the current 9, I assume you would have 2003 UB313, Ceres, and Sedna, at least. But I seem to recall several other currently known bodies in the Kuiper Belt larger than 850 km across, such as Quaoar, 2005 FY9, and 2003 EL61 as well as perhaps 2002 TC302.

I am very happy to see that the definition has some basis in the physical nature of the body and not some arbitrary cutoff, like 2000 km. While it may take some time for people to accept that Ceres will now be called a planet, I am glad that this whole non-sense is finally nearing an end and we can all get on with our lives.

EDIT: Okay, I think we can all agree that Charon is not a planet...

So, is the new nursery-rhyme mnemonic for the planets going to go something lik this?

"My Very Educated Mother, Catherine, Just Served Us Nine Pickled, Spicy Xylophones."



-the other Doug

Mmm...pickled spicy xylophones....

Interesting take from the IAU on this contentious issue. Ceres, though...looks pretty spherical from the HST images (which Dawn should amply confirm), as does Vesta despite its south polar divot...gotta wonder what Chiron's morpology is , as well as that of other Centaurs, and where to really draw a line that might mean something?

Point here is, obviously, that if this definition is rigorously enforced we may end up with a heckuva lot of planets, and that might get pretty cumbersome very quickly. Why not add a diameter provision (let's say that of Pluto, because it's probably a safe bet that there are many bodies bigger than 2003UB313 further out) as an additional requirement for planetary status? Like everything else in nature, the natural satellites of any star will exhibit a continuum of sizes rather than fall into nice, neat categories...gotta put this fire out now before it spreads.

And actually, let me present a new concept: the "Mercury Standard". Mercury is the smallest universally recognized planet, and its distinctive features with respect to planethood are that it formed independently as the result of accretion from the primordial Solar nebula at or near its present orbit. Using this logic, any body that is smaller than Mercury and in an orbit that exhibits any evidence of prior association with a major planet (the old "escaped moon" chestnut) would be excluded from planetary status. This would presumably eliminate Pluto, but perhaps admit Sedna and 2003UB313 if their respective orbital parameters are "clean".

I certainly have no problem with having a lot of planets. I say, the more, the merrier (Though if I had my way, we would have a couple of hundred thousand known planets, but I digress). I am just happy that some arbitrary cutoff wasn't chosen.

Personally, I am happy to see the inclusion of Ceres, though I hope that the objects I listed are not excluded and the list of bodies given by Spacedaily are just there extrapolation from the definition (particularly with the Charon inclusion, God I hope they meant to say Sedna).

Though the more I read, the more confused I am. What is this "pluton" non-sense? Will this have the same effect as "gas planet" and "terrestrial planet", or is this just an attempt to keep our heat-impaired comrades down? The idea of 8 "classical" planets bothers me a bit, again since it is a "exclusive" definition.

A wise choice. They have a nice physically-based definition instead of "I think Mercury is big enough, but Pluto isn't". Well worth the millions spent on their big meeting in Prague.

If they had reduced us to 8 planets and kicked out Pluto, many people would surely have been upset. It would have been hard to get concensus at IAU, which undermines it. And it would be harder to get funding to look for and study new Planets in the outer solarsystem.

Click to view attachment

But instead they gave us three new planets. TV news programs tomorrow get to tell everyone there are 12 planets, they get to introduce them to Ceres and explain it is named after the goddess of wheat or whatever. And nobody is going to be angry, because who has a grudge against Ceres?

Click to view attachment

So now the next pointless but irresistable debate will certainly be, what do we call 2003UB313?

Totally unrelated politics and political imagery removed. You all know the rules guys.

Doug

The relevant IAU press release can be found here:
http://www.iau2006.org/mirror/www.iau.org/...resolution.html



Yes indeed. This is an excerpt from the news text:

"For two or more objects comprising a multiple object system, the primary object is designated a planet if it independently satisfies the conditions above. A secondary object satisfying these conditions is also designated a planet if the system barycentre resides outside the primary. Secondary objects not satisfying these criteria are "satellites". Under this definition, Pluto's companion Charon is a planet, making Pluto-Charon a double planet."

Michael

I wonder what happens if the mutual orbits are eccentric and the barycentre moves in and out of the larger body every 'month'?

And just for good measure, an article about a backward polarity sun spot today describes sun spots as being 'planet sized'

PLANET SIZED

What the hell does that mean

Doug

Perhaps an "average" barycenter point can be taken as measure in that case. Say circularizing the orbits, leaving the orbital periods constant?

Pah! that's an easy one: 950 to 142984 km.

Personally, I have to admit that I feel rather uneasy about this proposal. People are liable to reject it on unscientific grounds because it provides 'too many planets'. Also, why do they mention only three planet candidates to the news, while treating other qualifying objects in a a separate, not-mentioned to the news category? I've seen quite alot of opposition already.

I think a slightly more acceptable definition would stress the difference between the 'dwarf planets' and the 'eight classical planets', thus allowing those who are so inclined to ignore the dwarf planets, while the inclusivists would include the dwarf planets.