Experts meet to decide Pluto fate, Finally we'll know what a 'planet' is... Options

[ljk4-1]

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

"Seed magazine links here, but predicts that you will be able to find out if Pluto is a planet here. No, you won't! I think this is an incredibly unimportant topic, it's not what this meeting is about and I will not mention it at all."

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.

[JRehling]

[...]

[Guest_AlexBlackwell_*]

I quite agree -- my question would be: why take the old, problematic term "planet" and try to shoehorn it into a nice, logical taxonomic system? It is precisely because the term is in the popular lingo that it's ill-suited for such a role. To me, trying to tinker with the popular term "planet", changing it, in order to get a useful taxonomy would be like trying to come up with a geological definition of "hill" as opposed to "mountain". Because there once seemed to be a sharp divide between planets and asteroids, the usefulness of the term was unquestioned. Now that the divide is known not to be sharp, the question is: why mold the term instead of working aroundit? People still have their nonscientific words for mountains and hills, and it doesn't hurt geology.

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.

This post has been edited by AlexBlackwell: Aug 15 2006, 09:06 PM

[DFinfrock]

This proposal is therefore to stay with the 75 years of popularly considering Pluto the Ninth, as the IAU agreed to in Manchester, and to adopt Xena as the Tenth Planet because it is intrinsically brighter than Pluto. The proposal is further that the same accurate and convenient criterion be used for naming an Eleventh Planet and so forth, namely that they be intrinsically brighter than Pluto, measured in “absolute V-magnitude.” Pluto's absolute visual magnitude is –0.76, Xena's –1.2.

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

[volcanopele]

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.

[dvandorn]

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

[Holder of the Tw...]

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.

[mcaplinger]

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.

[volcanopele]

? 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...

[dvandorn]

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

[nprev]

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".

[volcanopele]

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.

[Guest_DonPMitchell_*]

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.

[attachment=7015: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?

[attachment=7016:attachment]

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

[djellison]

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

Doug

[MichaelT]

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

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.

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