True, that is a fairly specialized group of kids, and some are certainly better at processing ambiguities than others.

Another sample I deal with on a regular basis is my 8 year old daughter and her buddies, whose interests run mostly to princesses, unicorns, and jump-rope songs. There too I have found that when I respond with "we don't really know, what do you think?", it usually results in a lively conversation.

I still think it's good to try to tackle these kinds of questions with children openly. Anything to get their brains switched on

I'll be blunt, I couldn't care less about this whole, planet/not a planet/what is a planet? debate. Personally, I think the whole thing is moronic. It has become obvious within the satellite systems of the outer satellites that size doesn't matter when it comes to how interesting an object is. I'm sure no one would argue that Rhea is a more interesting, scientifically, world than Enceladus, despite having a radius 3x that of a world that appears to be active. Mercury is surely not more interesting than Io, the moon more than Europa. And what does it matter what crowd you hang out with? Whether an object is with not so much smaller objects or ones that are MUCH smaller than you. Or whether you go around in a funny orbit, when it is so easy to go from a normal orbit, go by Neptune, and be in an inclined orbit.

So all this debate is just silly. If you seperate every thing into planets and non-planets, just make Pluto the cut-off and be done with it. If there turns out to be many objects in the KB that are larger than Pluto, then just not have school children learn all of them. It's not like they can look up in the night sky and see any of them. You just teach Pluto as the typical planet in the far outer solar system and say that there are X number of other planets as well as many more smaller objects orbiting in that region.

I agree with Mike Brown, "planet" is a culural term. As astronomers and planetary scientists uncovered the true complexity of the solar system in the last 40 years, "planet" ceased becoming an important term for describing what we are seeing scientifically.

Well, if you think about it, it never really was....the five planets were just those stars that moved that the ancients saw. When Uranus and Neptune were discovered, it was realized that they were similar, just more distant and hence fainter and so they were added. The problem happend with Ceres and the asteroids, as it was decided that they were too small. When Pluto was discovered, it was assumed its albedo was much less than it is (Additionally, since Charon wasn't discovered until 1978, most observations combined the light from the two worlds, making it seem brighter and hence larger), and I remember reading in a old book from the 1960s that it was 6,000 miles across! Now it appears that there is no size chasm between the inner rocky worlds and the worlds called asteroids and comets (I am assuming that, based on the way things are going, we probably haven't found the biggest of these worlds yet). The fact that the eight planets outsidet the Kuiper belt vary so much in size is a problem in and of itself - the ancients would have never realized that. I mean, in many ways Mercury has more in common with Ceres and Vesta than it does Jupiter.

The category was one made in ancient times. Neat models were made, in which the all the planets orbited in perfect circles with earth at the center. Secondary circles were made to compensate for discrepencies. When the Copernican revolution occured, the sun displaced earth, but the perfect circles continued until Kepler showed that orbits were elliptical. The powers that be were then angered as the telescope showed features on the moon, and then the planets, and worse, changing features - they were not perfect, changeless orbs. Also, some of them had moons of their own. People tried to make sense of this, and ideas like Bode's law seemed to make sense of planetary distances (a great coincidence). Theories developed that beginning with Earth having one moon, the patern would go 2 (Mars), 4(Jupiter), 8 (Saturn - the fact that Saturn and the planets beyond it didn't have that many known moons was at the time linked to their distance - surely they would be found!) and so on. The discovEventually, as I said earlier, two outer planets were discovered and the four outer planets were found to be the gas giants, very unlike the rocky worlds of the inner solar system. The discovery of the asteroid belt damaged this still relatively neat solar system, but this was turned backwards....the problem with Bode's law was that it predicted a planet between Mars and Jupiter - so it was assumed that this was it, but it had simply been smashed to rubble. Pluto became the odd-man-out, perhaps an ejected moon of Neptune. My point in all this is that our insistance on order in the solar system a deeply engrained cultural thing - people like order in the cosmos. Today, President Bush suggested intelligent design be taught in schools - a reminder of this. However, it now appears the ancient's view of the solar system is suffering yet another blow - It appears that the solar system is a messy place, with all sorts of objects lurking in its outer reaches. And we may have to redefine or abandon the word planet...If we were forced to re-categorize all the worlds in the solar system with no memory of tradition, it is unlikely that the gas giants would have ever been put in the same category as rocky worlds anyhow - it is scientific nonsense. In fact, Uranus and Neptune are quite different from Jupiter and Saturn, and push-come-to-shove, Jupiter is a borderline brown dwarf.

I haven't read the whole discussion here for lack of time, so I apologise if this repeats something already said.

One problem: people want definitions to be fences: a fence around certain objects called planets, another around objects called comets and so on. A fence definition is like 'over 2000 km diameter' or 'within 5% of being spherical' - a simple unambiguous test to decide if an object is in or out.

This worked in the 19th century! we then knew so few objects that a simple fence could surround each class of object. But now it doesn't work very well. In truth, the solar system has a complete spectrum of sizes, dust to Jupiter... a complete spectrum of shapes from Kleopatra to... uh.. Venus, a complete spectrum of ice versus rock composition and so on.

In this fuzzy universe, definitions really deal with core characteristics... they define a core and every object is a certain distance from it. Planets are large and orbit the sun... moons orbit planets... asteroids are small, rocky, and orbit the sun... comets are small, icy and orbit the sun. Then you look at a real object and it might have characteristics of several classes. Enceladus is a comet orbiting in its own tail (the E-ring)...

None of this helps... but we can't get too hung up on definitions because they are too fuzzy. I prefer to think of the word planet as a traditional designation with no very firm scientific definition. Pluto is a planet because since it was discovered it was called one. But all these objects are 'worlds'... to me.

Phil

Oh, don't be such a party-pooper, Phil. If the "news" media don't have this debate to talk about perpetually, they'll have to limit themselves to covering runaway brides.

2003-UB313 is not a great name for a planet -- and in fact, that's not what the discoverers call it. They've been referring to it as Xena -- after the television series about the Greek warrior princess. Xena was popular when the astronomers began their sweep of the sky in 2000.
http://www.cbc.ca/thecurrent/2005/200508/20050802.html

If I remember my greek correctly "Xena" translates as "female stranger"

tty

Nice diagrams!

I always make use of these verbal comparisons too when describing the planets to other people:

The Moon's surface area is the same as Africa
Mare Crisium is about the same size as Scotland
Mars has the same surface area as Earth's land area
Earth would neatly fit inside Jupiter's Great Red Spot

Are there any other, similar, comparisons out there (preferably not ones which use the size of Wales!).

I'm not sure the definition of "more or less a sphere" is -- my own criterion would be "can you make a cylindrical projection from it?" But this criterion has its own fuzzy boundaries (with weird moons like Iapetus sliding off the edge of it). But I don't quite see under which definition Vesta is "more or less a sphere"; to my eye, it's definitely "less" and then some. Likewise, there are no Jovian moons other than the Galilaeans that are "more or less" spherical. Five Saturnian moons are "more" spherical, with Iapetus and Mimas being borderline (and the example of Iapetus shows that major irregularity is not incompatible with large size; contrast the nicely rounded, but very small, Enceladus). Four Uranian moons are "more" spherical, with Miranda being borderline, and the rest irregular. Only one Neptunian moon, Triton, is round. But to determine sphericality, you can't just go by diameter or mass. No one would have predicted (or did) how irregular Iapetus actually is. Proteus is larger than Mimas but blockish rather than round. Quite possibly many of these KBOs are also very irregular despite large size. You actually have to observe their disks directly.



Which would be just, considering that it was one of the original list of planets, in the pre-Copernican systems. The reason for demoting it from planethood was not its size, but the fact that it did not revolve around the Sun.

Actually, Xena is a totally fictional TV character. There never was a greek female warrior named Xena. It's all fantasy.

Noting the lack of female named planets, I have suggested "Artemis" as a good name. Artemis was the goddess of hunting, nature and women in ancient Greece.
(Diana is the latin name, but that is already taken on earth )

I hope they name it Persephone. That was the name that James Christy originally intended to hang on Pluto's moon -- and it would have been magnificently appropriate poetically, given that it and Pluto perpetually keep their faces toward each other -- but by sheer dumb bad luck his wife was named Charlene and he felt the obligation to honor her, thereby both fouling up a beautiful metaphor and creating a moon which will forever be confused with Chiron. As for as I'm concerned, Christy's wife's real name is Mud. But in any case, Ceres' daughter is well overdue for an honoring.

damn there goes my favorite mnemonic:

my very efficient memory just stored up nine planets

There is an asteroid 399 Persephone; and also a 26 Proserpina (the Latin equivalent). This really ought not be any bar to the adoption of either of those names, as many of the asteroid names double the names of other bodies in the Solar System, like 593 Titania, 113 Amalthea, 577 Rhea, 106 Dione et cetera.
Although in looking for names of Roman gods to use for planets, "Minerva" and "Vulcan" seem to have been missed. And I dare say no one will want to name a planet "Bacchus"...

Tombaugh's group was actually leaning toward naming Pluto "Minerva" until that 11-year-old British schoolgirl came up with her famous suggestion. (Better than Percival Lowell's wife, who -- after suing for years to try and acquire all his observatory's funds for herself -- suggested that they name the planet after herself.)

I heartily agree. In my experience, fifth graders find it wonderful to discover that there are questions that no one knows the answer to.

One thing I find terribly sad about the intersection of public education and the "what is a planet" debate is that no definition of "planet" is likely to include fascinating worlds like Io, Enceladus, or Miranda. Kids are taught about Pluto -- a place we've never been to -- but not about Titan, a world that's bigger and much more dynamic than either Pluto or Mercury. In my book, "planets" are things that wander across the sky; "worlds" are places that we can (or have, or will) go to visit.

Sometimes tiny rocks like Tempel 1 and Eros get promoted to "world" status, and that's all right as far as I'm concerned. Explain to a fifth grader (or even a second grader) that if they jumped off the ground on one of those worlds, they'd fly off into space -- they think that's pretty cool. Especially if you jump up and down while you're explaining it to them. (You can invite them to jump up and down, too, but then you have to get them to stop!)

I have an old astronomy textbook from 1869 (no, I'm not THAT old ... I rescued it from an estate sale junk bin). Your post reminded me of this page in the book. Looks like Vulcan had been tried once before as a planet's name. (besides Spock's homeworld).

Click to view attachment

Yes, the Vulcan story is a classic of how Mother Nature keeps playing tricks on us. (I believe there was even a book published about it a few years ago.)

Short version: after it was discovered that Uranus wasn't quite where it should be in its orbit, the idea that there was another planet perturbing it was only one of the theories to explain this -- another was that Newton's gravitational law was very slightly off. The New Planet explanation -- namely, Neptune -- turned out to be the correct one. So when similar oddities were discovered in Mercury's orbit, the astronomical community naturally jumped to the conclusion that an undiscovered planet closer to the Sun than Mercury was, once again, the explanation -- and one unfortunate prominent French astronomer (can't remember who it was) actually swore that he'd seen the thing during a solar eclipse in (I believe) 1869. But that time, it turned out that the explanation really WAS subtle flaws in Newton's gravitational theory, as finally nailed by Einstein. There are times when it is hard to avoid the conclusion that God is pulling our leg.

How about Terminus, the roman god of borders out there on "the borderland of Sol" to quote Larry Niven? Or perhaps Boreas the greek god of the north (or the north wind at least). Or Thule, a semi-mythological land of the far north. However I agree that Persephone would be a good choice.

tty

But if you call it Terminus, we'll have to establish the First Foundation there, and that's just asking for a whole lot of problems down the road...

Seriously, Terminus would indicate a border, and I'm pretty certain that this new KBO is not the most outlying of the large KBOs out there. Let's save the distinction of the name Terminus for something that truly does mark a natural boundary.

-the other Doug

The observation that Neptune was discovered because people were trying to explain the disturbances in Uranus' orbit also brings to mind a debate we should have on what it means to "discover" a planet. We have 100+ extrasolar planets that have been "discovered" but never observed directly. Most of these "discoveries" are based solely on the inferred presence, size, and motion of an object based entirely on its effects on its parent star. So to be consistent, shouldn't we say that the person who discovered Neptune was the person who first hypothesized its existence based on the perturbations of Uranus' orbit? The actual visual sighting of Neptune was only the "confirmation" of its existence, using today's logic.

In a name discussion over on Usenet's rec.arts.sf.written, a poster dug up this article on the Beeb's website, published just after Sedna's discovery:


I'm not well versed on Arctic mythology - anyone else?

I'd prefer Persephone myself...

A pop science book I bought around 1981 came out and called the Galileans and Titan planets, although that author's notion did not become convention. Although the label "Lunar and Planetary Science" implicitly includes Phobos and Charon and Halley's Comet as "planetARY"... although oddly enough, the Moon is different enough that it needs its own half of the label!



Categories are powerful things -- people are surprised to learn that Reno is west of San Diego, and that Windsor, Canada is south of Detroit -- when the parent categories stand in one relation to one another, people assume that the members must all hold that relation to (CA west of NV; Canada north of USA). So, people assume that Mercury is more worth knowing about than Titan (and maybe it is -- that's debatable).

The analogy that I think of (maybe not the best for fifth graders) is of evidence at a crime scene. You want to understand the crime -- the best clues are not necessarily going to come from the largest objects in the room, or even the largest objects related to the crime. The killer's fingerprints (very small) may be more useful than his/her bootprints. A tiny drop of blood may be of more use than a discarded hat. In the same way, the isotopes of argon on Venus may tell us more about the origin of the solar system than do the bands in the clouds of Jupiter. And certainly some of the more exciting places in the solar system are smaller -- in fact, I don't know any solar system aficionados whose favorite world is the Sun -- and it's almost 1000 times more massive than everything else put together.

It's a pretty good bet that the largest US county doesn't have as much to see as Manhattan -- this could be an easy point to get across if you get past the "memorize the names of the nine planets" starting point. Maybe the best thing that can happen is that so many new planets are discovered that it becomes futile to learn their names and the rule of thumb becomes "Most planets are cold, barren iceballs; let's learn about the more interesting worlds."

That said, although the exciting worlds are usually the unique ones (Io, Europa, Titan) -- there's a lot to learn from comparing almost-alike pairs and sets of worlds, and the icy midsized moons plus the uranian satellites make a fascinating study on planetary evolution even though most of them are less than spectacular individually. The most interesting thing about Pluto -- and now Planet 10 -- may be comparing them to each other.

The 2003 UB313 discovery page now includes this:

"Though we tried earlier to measure the size using Spitzer, those observations failed due to a technical glitch. We are trying again! The new data will be down by the end of the month."

Didn't they base their size estmates on the fact that Spitzer was unable to detect it?

Yes, but as I understand it, the lack of a Spitzer observation sets the upper estimate only.

The lower estimate was set by assuming 100% albedo, it would be about the same size as Pluto.

So if Sptizer does see it now, it may be even bigger than the original upper estimate...

Short IAU statement:

http://www.iau.org/IAU/FAQ/2003_UB313.html

Spitzer observation schedule for the last week of August (not yet up):

http://ssc.spitzer.caltech.edu/approvdprog...lan/week092.txt

HST proposal:

http://www.stsci.edu/cgi-bin/get-proposal-info?10545

Depends what you mean by hypothesizing. Because Neptune was discovered near the position it was expected to be according to LeVerrier, he deserves the discovery credit. One would say that he discovered it by its gravity. Those who claimed that there should be additional giant planets (Lowell, Pickering et al.) don't deserve the credit even if one was found, because they did not make accurate/correct predictions.

Nope. In the case of Uranus' subtle, slow orbital perturbations, they might well (like Mercury's) have been due to flaws in Newton's theory rather than to a new planet. In the case, of the extrasolar planets, however, we're seeing some stars do a persistent, circular jig while others do not -- and the only remotely plausible reason for that is that they are being orbited by large planets.

Personally, as a kid I would have been far more interested to learn that the number of planets was really indeterminate, and dependent upon definition, than that it was a boring old nine. And, as John says, it's not the size of your world; it's how interesting it is.

That's right. Still, it seems to have Pluto-like surface (although it's not reddish like Pluto), so it may have relatively high albedo like the other two new giant KBOs.

OK -- here's a gedankenexperiment.

You have God's Magic Eight-Ball. You can only ask it the following question: "How many planets does this particular star have?" It can only give you a number back.

What answer is more helpful to you -- four, 12, or 33,117?

A classification system that is *too* inclusive makes it less useful.

-the other Doug

More information on the possible name:

http://www.sacbee.com/content/news/science...-14199188c.html



Perhaps this will carry through to the official name...

deleted double post apologies ...

Xena is female ?

Unless you happened to know a lot about the planets when you were young. In 4th grade, the teacher exempted me from the platetary lessons, because she said I knew more about the planets than she did. I could tell you the orbital times of most planets, how many moons they had, and the names of some of the larger moons. I knew all of the Galilean Satellites, and of course, Titan. Miranda, Triton, Charon....fun times.

Seeing that you knew Charon's name when you were a kid makes some of us feel mighty old - it doesn't seem THAT long ago that we didn't know that Pluto had a moon!

If I REALLY want to make myself feel old, I can remind myself that I visited Hawaii before it became a US State! On the way from Japan (where I was born) to the US, our ship stopped in Honolulu in June 1957.

If you feel old, I feel like a newborn... the first moons I remember being discovered are Caliban and Sycorax in 1997. I was alive for the Neptune tour in '89 and Pan in '90, but considering I was 2-3 years old, I don't quite remember them.

Personally, I don't think it's silly to ask a definition of planet. Sure it's a wide category, but I think we're stuck with it now, whether we like it or not. I don't think any dictionary editors will be fazed even by the IAU calling them up and telling them what a planet is.

When I took my high school astronomy classes, there wasn't much about the moons at all. When we took notes, maybe one little note about each of the Galileans and Titan. And that was about it. I was quite disappointed, although at that point I didn't expect I'd learn anything new.

As for being able to name the planets and moons, I still pride myself on it. Well, more on the moons, since there are so many of them nowadays. And speaking of which, the issue of what's a moon is still open, too... unless someone wants to catelog each and every ring particle out there as one.

Considering this post and Emily's earlier, I am starting to think that a lot of angst over the "planet" label might be eased if someone issued an "authoritative" list of the Ten Most Interesting Worlds, to keep people from mistaking the label "planet" with "most interesting". Of course, this would still be political as hell, and people would argue about what number to stop at, but at least it would keep people from assuming that what's not a planet isn't interesting. The point would be more of an educational canon -- nothing scientific.

I'd say that a good solar system education should pay special attention to these worlds: Earth, Sun, Moon, plus a topic each for Venus, Mars, Jupiter, Saturn (rings), Uranus/Neptune, Pluto/KBOs, Io, Europa, Titan, asteroids/comets/small satellites. That covers just about everything in ten topics.

Maybe that's the solution to the "planet" problem. Let's just call 'em all "worlds".

A "ten most interesting worlds" poll might be kind of fun...

...but I've already thought of a quandrary: I think Saturn's rings are awfully cool, but find Saturn itself rather boring. Do rings count as part of a planet, or are they a "world" in themselves? Or worlds?

I do apologise for drifting off the TNO topic. Maybe we need a "what's a world? / what's a planet?" thread.

How about if the body is large enough to have tectonics or volcanisms we call it a planetary body. That brings in Enceladus, Miranda and Vesta.

And Triton. Don't forget the liquid nitrogen geysers....

Chris

I dont think you can judge a body on it's nature, only it's 'stats'

At some point - you're always going to have to make an discreet cut-off, be it size or some other parameter.

I thinn the phrase 'planet' should be reserved for anything that orbits the sun and is over X km. Anything that orbits a planet is a moon. Anything smaller than X is a minor planet.

I'm in favour of semi-arbitrary cut-offs, but I think it should be mass rather than diameter, just like the present upper limit (13 Mjup). Planetary satellites could be called 'secondary planets' and be categorized in exactly the same way

How about:

'World' planets (bodies containing less than 5% molecular hydrogen):

0 < m <Mmimas = minor planets (takes out most of the aspheroidal bodies)
Mmimas < m < Mmercury = dwarf planets/small planets/mesoplanets/planetoids
Mmercury < m < 5 MEarth = major planet
5MEarth < m = super planet (none known to exist)

I think there should be a separate classification for objects composed of between 5% and 50% molecular hydrogen. Uranian planets? Ice giants? I don't think they belong with the Jovians or with the 'world' planets.

Jupiter and Saturn are different again. Gas giants, Jovians, call 'em what you will. I see them as the dwarf end of a range that has stellar bodies at the upper end, not as giant versions of bodies like Mercury.

Bodies with > 50% hydrogen

? < m < 13 Mjup = jovians
13 Mjup < m < 90Mjup = brown dwarfs

Should be some </= signs rather than < signs here, but you get the idea...

Another insight into the forthcoming IAU decision:

http://www.sfgate.com/cgi-bin/article.cgi?...MNGU5E4K2Q1.DTL



Don't like this idea at all. Yes, the label 'planet' is in common usage, but that isn't a good reason to continue propogating it (especially if it becomes as meaningless as this proposal would make it). It's a sign that there is a major barrier between the public and the astronomical community; one that needs to be broken. To do otherwise is patronising and carries the assumption that people are too stupid to understand more a short list of the names of ancient gods.

I think culture would appreciate the word 'world' more than 'planet' or 'moon' anyway. Which sounds more funding-worthy:

A mission to 'Saturn's biggest moon, named Titan'
or
A mission to 'a world named Titan'?

'Planet' belongs in the era of naked-eye to telescopic astronomy. It's a name for bright lights in the sky that change position relative to the crystal vault of the heavens.

It's not a name for places that humans drive remotely controlled vehicles across the surface of.

How about Tombaugh?

Maybe the list of planets won't get so crowded after all. Some of the brighter KBO's may not be as large as has been assumed. Instead they only have a brighter surface.
Albedos, Diameters (and a Density) of Kuiper Belt and Centaur Objects

Several updates at:

http://www.gps.caltech.edu/~mbrown/planetlila/index.html

Nat Geo article:

http://news.nationalgeographic.com/news/20...w_planet_2.html




Also:

Spitzer observations of 2003 UB313 on 25 & 26 August.

2003 UB313 currently listed as H = -1.1 (data-arc = 1954-2005)
2005 FY9 currently listed as H = -0.2 (data-arc = 1955-2005)
2003 EL61 currently listed as H = 0.1 (data-arc = 1955-2005)

It seems almost certain to me now that if it is recognized as a planet, it will be a feminine name probably between Persephone/Artemis/Minerva.

Personally, my vote's for "Yuggoth". Fans of H.P.Lovecraft will understand.

ALF once had names for the two planets beyond Pluto. They were something like Dave and Steve. Anyone remember? Or care to admit they know?