Grandfathering Planets
Posted February 23rd, 2006 by Howard TaylerPluto is a weird planet. So weird, in fact, that lots of respectable scientists want to call it NOT a planet.
My own view on the matter is that calling something a planet is like naming your dog. It’s arbitrary. Completely arbitrary. For any definition of “planet” you come up with, you’re going to find objects in this universe that fit, yet defy explanation… unless your definition of “planet” is “one of the nine celestial objects either named for the greek gods or conveniently right underfoot, those being Mercury, Venus, Earth (underfoot), Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.”
Does a planet have to have moons? Nope. Venus and Mercury are both moonless, and Pluto now has THREE.
What about atmosphere? Hmmm…. Titan has atmosphere, but it’s only a MOON. Mercury has no atmosphere either. It has an exosphere — elements from its crust that have been knocked free by high-energy radiation from the Sun, and which are so rarified that they never collide.
And don’t get me started on size. Pluto is smaller than non-planetary objects, and Titan is larger than Mercury.
Well… maybe “it has to have atmosphere or exosphere, has to be at least so large, but it can’t be orbiting something else (besides a star).” Okay, now it’s starting to sound arbitrary.
But I’m fine calling Pluto a planet, because “Planet” these days includes objects so dissimilar that the only thing they all have in common is a name scheme. Mercury, Venus, Earth, and Mars are all rocky worlds with thin atmospheres (neither too thin nor too thick in Earth’s case). Jupiter, Saturn, Uranus and Neptune are all gaseous worlds that are almost ALL atmosphere. Pluto is a Kuiper-belt object orbiting in a different plane, and which appears to actually be a clump of Kuiper belt objects caused by a collision billions of years ago.
Kids learning astronomy need to have “hooks” to hang information on. The word “Planet” is a good hook. Scientists, on the other hand, need to be able to let go of oversimplified generalizations. The current arguments about “planet or not-a-planet” are irrelevant. Pluto is a thing, different from some things and similar to others. Categorizing it or re-categorizing it will not change its nature. You can’t turn your dog into a cat by calling it “Kitty.” You CAN confuse your children, though.
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February 23rd, 2006 at 12:10 pm
Well said!
What’s in a name? that which we call a rose
By any other name would smell as sweet;
– Romeo and Juliet (II, ii, 1-2)
February 23rd, 2006 at 12:15 pm
Just to correct a slip, Howard, Titan is larger than Mercury, not Mars.
As for the rest, firstly, the definition of a planet is not nearly as confusing as you suggest. It has nothing to do with atmospheres, only with size and orbit. A planet is an object of sufficient size (but still small enough not to undergo nuclear burning like a star) in orbit around a star. The only debated point here is the lower limit, the ’sufficient size’. There has never been any question regarding Titan, despite it being larger than Mercury, as it orbits Saturn, not the Sun.
Categorizing things correctly is important, and far from arbitrary. If you had been calling a Pekingese a cat for years (hey, it’s smaller) before discovering it was in fact a dog, would you want to continue to call it a cat? Since Pluto seems to be a Kuiper belt object (now that we have observed more of them) isn’t it better to call it one? Or, consider calling all large Kuiper belt objects planets? Would that not be less confusing and more useful in the long run, than sticking to calling it a planet while calling the other Kuiper belt objects something else?
Things get recategorized all the time, as our understanding improves. Hanging on to outdated terminology is more confusing, not less.
February 23rd, 2006 at 12:31 pm
Fixed the misquote on Titan — yeah, I knew that. What is it with “M-”planets, anyway?
Re: outdated terminology… Science doesn’t do a good job at driving usage for the lay person. As I see it there are rocky worlds, gas giants, kuiper objects that stay outside the inner system, kuiper objects that loop INSIDE the inner system, Oort objects in both those categories, and asteroids. Oh, and any of these objects may end up as a satellite to any of the others (though we’ve yet to find one gas giant orbiting another, I suspect it’s only a matter of time.)
It would be helpful to have words for all of these that were related in such a way that knowing the word also allowed the speaker to know the relationship between the objects. But like the classification of stars by luminosity, it’s not something a lay person would ever grasp.
February 23rd, 2006 at 12:39 pm
Patrick Moore was quite adamant in the January episode of The Sky at Night that Pluto wasn’t a planet. I *think* the reason he gave was that it was a Kuiper Belt object come in for a cup of tea and a sit down, but I might be wrong and I’m certainly no expert myself.
The episode’s not available online yet, but should be soon.
February 23rd, 2006 at 1:34 pm
I had a couple of small email chats with the guy who discovered UB313 (the KBO that is larger than Pluto), here’s his site: http://www.gps.caltech.edu/~mbrown/planetlila/
In it he argues that although he was once one who decried Pluto as a planet, since he’s discovered one bigger he’s now changed his mind. Can’t argue his point as it makes sense.
I for one believe that any object with suffecient mass to become spherical should be named a planet. You can say that Pluto inhabits the Kuiper belt, but many don’t know that Jupiter has asteroids in it’s orbit called Trojans (granted Jupiter out sizes/masses them all combined!). What happens if we find a Mercury or Mars sized planet in the Kuiper Belt area? Not to mention what we might find in other solar systems.
I say: Orbits? Schmorbits! If it’s round, it’s a planet. Scientists already use the term Major and Minor Planets anyway. Let ‘em call ‘em what they want.
February 23rd, 2006 at 1:55 pm
The planets are actually named after Roman gods, not Greek ones.
February 23rd, 2006 at 2:25 pm
Isn’t confusing kids the primary point of interacting with them?
February 23rd, 2006 at 2:36 pm
strangely, planet comes from a greek word meaning “wanderer.” I think we should stick with the ancient definition. the SEVEN planets are Mercury, Venus, Mars, Jupiter, Saturn, Sol, and Luna.
This definition is logically consistant, and even scientifically applicable: a planet is an object in the heavens which can be observed with the unaided eye, and appears to move on at least a daily timescale with respect to the “fixed” celestial sphere.
actually, sol could be excluded if you presume that all observations take place from the surface and require the ability to actually observe the celestial sphere and the object at the same time.
February 23rd, 2006 at 4:38 pm
I’d go with the following set of definitions, myself:
1) A star is any body massive enough to sustain nuclear fusion or to have sustained it during its existence.
2) A planet is any body that insufficiently massive to sustain fusion that is massive enough to be spheroidal under its own gravity.
3) An asteroid is anything smaller.
4) A primary is any body that primarily orbits the center of the galaxy; a secondary primarily orbits a primary, a tertiary primarily orbits a tertiary, and so on.
5) A moon is a special term for any tertiary or later planet, or any secondary planet the same orbit as a larger secondary planet. (Asteroids/irregular moons no longer count, which has the advantage of fixing the number of moons of the gas giants reasonably, and solves the question of how large a ring chunk has to be before it’s a moon.)
6) The term “major planet” is grandfathered for the nine secondary planets in our solar system defined as such as of 1950.
So, under this classification, Pluto is a secondary planet and a major planet; Luna is a moon and a secondary planet; Titan is a moon and a secondary planet; Ceres is a secondary planet; UB313 is a secondary planet.
Mercury, Venus, and Mars are secondary and major planets without moons; Earth, Neptune, and Pluto are secondary and major planets with one moon each; Jupiter is a secondary and major planet with four moons; Uranus is a secondary and major planet with five moons; Saturn is a secondary and major planet with seven moons.
February 23rd, 2006 at 4:39 pm
MOST of the planets other than Earth are named after Roman gods. Uranus was, in fact, a member of the Greek pantheon.
So says the guy who did way too much research for a Sailor Moon fanfic.
February 23rd, 2006 at 4:40 pm
Agggh! Two mistakes — Teritaries orbit secondaries; Titan is a moon and a *tertiary* planet.
February 23rd, 2006 at 5:05 pm
^.^;; My dog answers to “Here, kitty, kitty” all the time…
February 23rd, 2006 at 5:20 pm
“You can’t turn your dog into a cat by calling it “Kitty.” You CAN confuse your children, though.”
That explains why I was so confused about cats and dogs for the longest time…
now my parents also called pants shirts, and vice versa. When I was told to take my shirt off to play on skins back in highschool gym class… let me tell you, it was an embarrassing moment… ;)
February 23rd, 2006 at 7:22 pm
Your HS gym class had “shirts” vs. skins? Either it wasn’t a mixed sex HS, or I went to the wrong one….
February 23rd, 2006 at 7:39 pm
Planetmongering Lunatic, your classification scheme would have the advantage of being (mostly) unambiguous and consistent (though just how spherical does something have to be to be a planet not an asteroid?), but I can’t see something like that catching on generally. It requires too much knowledge of the subject for the lay person to properly understand it, especially the planet/asteroid divider. It’s the sort of thing that might appeal to scientists, but astronomy does has a tendency to stick with old classification systems and nomenclature long after more sensible alternatives are available (e.g. the magnitude system, stellar spectral type classications).
Your definition of a star is similar to the official one, however by having everything below the fusion limit be a planet you end up lumping brown dwarves into the same category, which just doesn’t seem right to me.
Also, the way that planets orbiting the secondary in a binary star system would be classified a level below equivalent planets orbiting an isolated star seems a little arbitray too.
Basically, I think I’m agreeing with Howard on this. No matter how hard you try to be purely objective, consistent and logical in defining what a planet is the variety of the universe keeps forcing you into making arbitrary cutoffs, which will eventually lead to incosistencies when new oddball objects are discovered, so you may as well not worry too much about it.
The decision on whether UB313 is a planet or not isn’t completely unimportant however. Until the International Astronomical Union decides what sort of object it is it can’t be given an offical name, because the rules for naming planets are different than for naming asteroids/comets/etc. With a bit of luck a decision will be made by the end of the General Assembly in August, as UB313 just isn’t catchy enough to be using long term.
February 23rd, 2006 at 7:42 pm
I like the idea of people 80 years from now still discovering planets. My vote: Something Pluto sized or larger that orbits the sun is a planet. The fact that Pluto has 3 moons strengthens its claim I think as you could argue: “Planets have moons and important planets have BIG moons! (Or at least lots of them.)”.
Pluto’s moon is the largest relative to the size of its planet, and if you argue, “well, it isn’t THAT big then Pluto can fall back on having lots of moons”.
Regards, Rick.
February 23rd, 2006 at 7:46 pm
I say, a planet is:
A self-contained object that origionally was in direct orbit around a star.
February 23rd, 2006 at 7:56 pm
Reg:
There’s no “official” definition from the IAU – International Astronomical Union, the group that takes care of nomenclature for all astronomical bodies. They’re supposedly working on it.
Planetmongering Lunatic:
I like your list. I’ve got a similar one: not official, but some star formation people I’ve talked to like it. Unfortunately, since it’s really a continuum from stars to planets to other, any line we draw is going to be somewhat arbitrary.
1) If it sustains nuclear fusion of Hydrogen, it’s a star.
2) If it does not sustain Hydrogen fusion, but does sustain Deuterium fusion, it’s a brown dwarf.
3) If it does not sustain any fusion, is round from self-gravitation, and is more massive than all other objects with similar orbits combined, it is a planet. (“Similar orbit” to be definied; I’d say something like +/-5% on the radius?) Such objects typically orbit stars.
4) If it is not more massive than all other objects with similar orbits, and primarily orbits a planet, it is a moon.
5) If it is not more massive than all other objects with similar orbits, and does not primarily orbit a planet, it is a minor planet. This includes asteroids, Kuiper Belt objects, comets, and probably Pluto, Sedna, Quaoar, and “Xena.”
Within the category of stars, Annie Jump Cannon empirically classified types (by mass or temperature), and Subrahmanyan Chandrasekhar devised the theory behind it. The study of sub-stars (brown dwarfs, planets, and minor planets) is still at the “counting and naming” stage (see Williamina Fleming for the equivalent stage in stellar classification history), but we’ll get to the theory eventually.
February 23rd, 2006 at 8:10 pm
A planet orbits a star, and only a star. It is very minorly, if at all, affected by the gravity of non-stellar objects.
An asteroid is a large peice of rock, larger than a meteor but not large enough to be spherical without an alternate source of gravity. A moon is an asteroid orbiting a planet.
That’s as good as I can do, but I think it covers it. I guess some meteors are considered moons in some astronomical circles, but not any I subscribe to.
February 23rd, 2006 at 8:35 pm
I reckon people will definitely still be discovering planets in 80 years time, however they might not be in our own solar system… ;-) The planets around other stars are already a significant (and growing) part of observational astronomy.
This subject was discussed at work at while back (I’m an astronomer), and there seem to be a number of possible definitions that ‘the professionals’ have put forward.
1. Everything in orbit around the Sun (and not gravitationally bound to another solar system object larger than itself, i.e. not a moon) that is at least as large as Pluto is a planet. The maintains the status quo with respect to Pluto (no need to update all those school textbooks…) but requires that UB313 be classified as the tenth planet. Making the distinction between planet and not a planet amongst the Kuiper Belt Objects purely based on size is completely arbitrary though, as a KBO marginally smaller than Pluto isn’t really that different to one marginally bigger. Also some people have argued that if dozens of Kuiper Belt Objects larger than Pluto end up being discovered it might ‘devalue’ the term planet, and lead to a need to subdivide the classification later into ‘inner’ planets and ‘all those hundreds of not very interesting big Kuiper Belt Objects that no one learns the name of’ planets so it’d be better to make that distinction now rather than later.
2. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are planets, and everything else isn’t. Pluto and the other Kuiper Belt Objects are qualitively rather different to the rest of the planets (in terms of orbits, sizes, composition, etc.) so this makes some sense. This relegates Pluto from being a planet to being a Kuiper Belt Object, which is bound to upset some people, but it guarantees (almost) that we won’t have to make anymore difficult decisions in the future as the number of planets is fixed. As compensation to those who think that Pluto should retain some special status instead of just being classified as ‘one of the bigger Kuiper Belt Objects, and the first to be discovered’ one of my colleagues suggested classifying the large KBOs (or Pluto size or larger, say) as a new type of object with a name which reflects Pluto’s status as the prototype, ‘Plutoids’, for example.
3. The nine objects currently called planets are planets, and everything else isn’t. This is the minimally disruptive, status quo maintaining option. It’s very difficult to make a logical argument for Pluto to be a planet while UB313 isn’t, but most people won’t care about the inconsistency, people already call Pluto a planet so that’s just the way it is.
Personally I think 2 is marginally the best option (I like the idea of ‘Plutoids’) but I’d be happy enough with 1 too.
February 23rd, 2006 at 8:38 pm
I believe class M was just a term made up by Gene Roddenbery. I think his reasoning for the term is explained in a book I’ve got. If I recall correctly, it was “Why? Why not?”
February 23rd, 2006 at 8:43 pm
Brickwall, your system has a lot of solar system moons not qualifying as being anything, as they’re large enough to be spherical due to their self-gravity but aren’t in direct solar orbits.
Meteors have a very specific definition already. They’re specks of dust/grains of sand/pebbles that hit the Earth’s atmosphere. If they’re big enough to make it to the ground without totally burning up then the lump of rock is called a meteorite. These certainly aren’t moons of anything, and also aren’t distinct from asteroids. An small asteroid in an Earth-crossing orbit may well become a meteor, and it it doesn’t hit the ground too hard end up as a meteorite.
February 23rd, 2006 at 9:22 pm
Ceres was downgraded from “planet” to “asteroid.” Tradition is a stupid reason to call a KBO a planet, especially in science. Unless we want to call earth, air, fire and water elements.
Pluto’s a snowball. It’s status isn’t “now under question,” it’s BEEN under question since it was discovered–too small (And smaller every time it’s looked at with better gear), odd structure, odd orbit.
As for thinking of the poor children, how will they feel when there’s 50 of these danged things to memorize?
And the discoverer decided he’d rather be credited with the 10th planet than the 2nd KBO? Oh, what a surprise. Of course, he’s a totally disinterested party. :rolleyes:
February 23rd, 2006 at 9:45 pm
I say we just call anything bigger than a certain size a planet and then make the kids learn some incredibly long mnemonic trick just to pass third grade.
February 23rd, 2006 at 10:06 pm
Honestly, I think the whole thing is a stupid argument. Put simply, the Terrestrial Planets (Mercury, Venus, Terra (Earth, where the word Terrestrial comes from), and Mars) are qualitatively different from the Jovian Planets (Jupiter, Saturn, Uranus and Neptune) which are qualitatively different from the Asteriods (Ceres, Hektor, etc) which are qualitatively different from the Trans-Neptunian Objects (Pluto, Sedna, Quoaor etc.) The Jovians may or may not be qualitatively different from the Super-Jovian ‘planets’ we’ve discovered in orbit around other stars.
The fact is, these things shouldn’t be lumped together. It implies a similarity where none exists.
At the end of the day though, we’re stuck with the word ‘planet’, even though it is becoming less and less useful. That being the case, I’d honestly like to toss Pluto back and restrict the label based on two properties. Objects which orbit a star, and which have, through internal heating, undergone chemical layering. This gives you a nice set of criteria which includes the terrestrials and the Jovians, but will very likely leave out anything we find out in the Kupier Belt and Oort Clouds.
February 23rd, 2006 at 10:46 pm
Apparently Isaac Asimov (ommmmm) suggested ‘mesoplanet’ for things Plutonic-sized. It works for me, but will it work for the snail-like IAU?
I was wondering about the moonlets’ names today, too. ‘Thanatos’ is apparently not taken, but ‘Orcus’ and ‘Hypnos’ already are, drat it. ‘Cerberus’ is too nifty to use up on something so small. Maybe the rivers of the Underworld, then?
(Nidoking — I want soooo bad for Sailorsedna to be some embittered lonely outpost senshi. *wink*)
February 23rd, 2006 at 11:20 pm
I like the name “Plutoids.” That’s a good name.
February 23rd, 2006 at 11:25 pm
I remember from Astronomy class that astronomers have (in essence) wound the clock back far enough, tracing the planets’ paths (and yes, Pluto counts) and a few billion years ago, guess what? *SMACK* Pluto and Neptune had a little bitty run-in. They hypothesize that this collision is 1. why Neptune has a retrograde orbit (rotates opposite its orbit), and 2. why Pluto is now in orbit around the Sun. In fact, from [http://cse.ssl.berkeley.edu/AtHomeAstronomy/act09_planet_list.html]:
“Because Pluto’s orbit is quite elliptical in shape, at times Pluto travels closer to the Sun than Neptune’s orbit. This was the case from January 1979 through February 1999, when Neptune was the farthest planet from the Sun.”
And who is to argue with the Animaniacs? (lyrics from one of their shortest songs)
The closest to the Sun
Is the planet Mercury.
Next is shrouded planet
Venus, it’s a cloudy mystery!
The next is Earth, we call it home,
Let’s hope it stays that way!
And next is Mars, it’s really red,
What more can we say?
We travel on to Jupiter,
It’s big as planets come.
Then there’s Saturn with its mighty rings
Made up of tiny crumbs!
Further out is Neptune
It’s a gassy, freezing ball.
And lastly there is Pluto,
It’s the furthest one of all!
Well, that’s all the plan–
… Goooood night, everyone!
:-)
So, let’s let Clyde W. Tombaugh have his due and quit picking nits. It is a planet. End of story. Bye-bye. :-)
February 23rd, 2006 at 11:28 pm
Darn. It cut out the line
“You forgot Uranus” before the good night everyone line. Darn brackets…
February 23rd, 2006 at 11:34 pm
Brian Kristopher said: That being the case, I’d honestly like to toss Pluto back and restrict the label based on two properties. Objects which orbit a star, and which have, through internal heating, undergone chemical layering. This gives you a nice set of criteria which includes the terrestrials and the Jovians, but will very likely leave out anything we find out in the Kupier Belt and Oort Clouds.
——————–
You will find there are several asteroids of spherical nature that fit your definition of “planet.”
February 23rd, 2006 at 11:50 pm
Neptune doesn’t have retrograde rotation, but Pluto does (opposite rotation direction to the majority of planets). A retrograde orbit would be something rather more dramatic, going round the sun in the opposite direction, but none of the planets do that.
Pluto has always been in orbit around the Sun, but its orbit has certainly been altered by Neptune. I’m not sure about any close encounters but Pluto has been under the gravitation influence of Neptune for the majority of the history of the solar system, and this has determined Pluto’s orbital period (it’s caught in a 3:2 orbital resonance such that 3 Pluto ‘years’ equal 2 Neptunian ‘years’). There are about 150 other known KBO’s trapped in the same 3:2 resonance (plutinos), and others caught up in other resonant orbits further out.
February 23rd, 2006 at 11:55 pm
We’re missing a point here, I think. Scientists aren’t happy unless they’re arguing over quibbling little semantic points.
These guys have neutron sources and laser beams. We want to keep them happy, right?
February 24th, 2006 at 12:08 am
A friend pointed out that the only reason the classification is controversial… is that it determines whose funding is used to study them :-)
February 24th, 2006 at 12:10 am
Heheh.
I think the main problem is actually that people are looking to a group of scientists (the IAU) to agree on a definitive answer to something they think is a scientific question (Howard and the people commenting here know better, of course) but which is in fact just a quibbling little semantic point. The scientists have then tried to approach the problem from a scientific basis (as that is what people seem to expect) in order to persuade each other towards an agreement but that just doesn’t work because (as pointed out here) it’s all about scientifically irrelevant nomenclature.
I’ve discussed the issue with people that are part of the IAU working group on the definition of a planet, and they’re just fed up with the whole enterprise because they can’t agree on anything. When presented with something like this most scientists would prefer to let someone else argue semantics while they get stuck into a proper scientific problem where there’s some prospect of persuading others you’re ‘right’.
February 24th, 2006 at 1:16 am
‘ I believe class M was just a term made up by Gene Roddenbery. I think his reasoning for the term is explained in a book I’ve got. If I recall correctly, it was “Why? Why not?” ‘
http://memory-alpha.org/en/wiki/Planetary_classification
Has all the names for the ‘classes’ of planet, though this link might just be useful to the whole ‘wtf is a planet?’ debate;
http://memory-alpha.org/en/wiki/Planet
Using both links, Pluto, I think, is still classified as a Planet.
When in doubt, turn to Star Trek; taking technobabble and turning it into layman’s terms since 1966.
TTFN,
Phil
February 24th, 2006 at 2:33 am
“I was wondering about the moonlets’ names today, too. ‘Thanatos’ is apparently not taken, but ‘Orcus’ and ‘Hypnos’ already are, drat it. ‘Cerberus’ is too nifty to use up on something so small. Maybe the rivers of the Underworld, then?”
That’s a kinda silly position:
“Well, we’ve found another moon orbiting mars”
“Well, the first one’s called Phobos. I was thinking Diemos”
“Nah, Diemos is to scary, and it’s a really small moon. Lets just go with Fred”
Cerberus is a perfect name for a pluto-orbiting object, and I find it extremely fortunate that it’s not taken.
Prosperina (or Persephone) would have been my choice for the other object, but those are both taken. Is there a Dis yet?
February 24th, 2006 at 2:53 am
Hey, folks, reality check here. I’m a science teacher. Do you have ANY IDEA how COOL it is to be able to say “How many planets are there?” “Nine? Bzzzzzzzzzzzt! Wrong answer! Either eight or ten!”
All facetiousness aside, it’s always good to check and recheck nomenclature against new information. FWIW, I don’t think there’s any reason other than history to call Pluto a planet. But either it is, whereupon if we are consistent then we recategorise a bunch of Kuiper belt objects as planets too (please don’t, that’s messy) or we reassign the useless iceball off to the Kuiper belt itself, which is where it belongs. Don’t give me the half-baked idea that nothing has changed!
February 24th, 2006 at 3:54 am
I don’t really understand why folks are so vehemently opposed to calling Kuiper belt objects “planets”. I mean, are you all close friends of Mr. Kuiper, or what? “Kuiper belt object” is not a very good name, anyway. It’s 3 words long, for starters, and “object” is about as descriptive as “thing”. So “Kuiper belt object” merely describes “a thing found in the circular (belt-like) region discovered by some guy named Kuiper”. Which Pluto, by definition, is not, since it is not in that region. There is no such thing as a Kuiper belt object which is not in the Kuiper belt. Duh.
February 24th, 2006 at 3:56 am
3 moons for Pluto, drat, that throws a monkey wrench into Roger MacBride Allen’s “Ring of Charon” and several other SF novels and short stories involving Pluto… so did the discovery of Charon. ;)
I say leave history alone. Pluto’s a planet because it was the ninth solar orbiting, non-asteroid, object discovered before anyone even thought about KBOs.
Divide the KBOs into over and under Pluto size and be done with it.
Moons, either spherical objects orbiting a planet, or in the abscence of spherical objects orbiting the planet, any chunks of matter of any shape 75% or higher above the median* size of everything orbiting the planet. That leaves Mars’ two moons as moons instead of random junk.
*With a median, unlike an average or mean (which are the same thing) there cannot be more or less than 50% of a set above or below the median. The median is whatever is right in the middle once the group is divided into two equal halves. So when some politician says something like “More than 50% of schoolchildren are below average in math.” he’s NOT a math dunderhead. If he said _median_, get out the math cluebats…
Going by Saturn’s collection of orbiting junk, there’s certainly few enough objects in the upper 25% of the size range to keep the number of qualifying moons down to something manageable. Saturn is a special case though, it has outer moons that’re spherical and orbit from almost smack against the outer edge of the rings to so far out they’re >thisclose
February 24th, 2006 at 4:33 am
I can solve the whole problem quicker and easier than the IAU and I only have one simple rule.
1. It’s a planet if I say it’s a planet.
There, done. Pluto is a planet, so is Xena. So are the rest of the traditional 9 planets, and by traditional I mean the ones that were planets since I’ve been born. You may refer to that as the Crane Astronomical Calender if doing such things makes you happy, and judging by the love to argue what a planet is, it probably does.
For all other discoveries please contact me by email, provided for use by the IAU as well, with photos and data and I will give them the once over to announce what you have gotten your mits on.
I will be completely discrete and no amounts of money will be able to sway my decisions, though I do have a small group from Madagascar who are offering quite a good some of money for me to reclassify Mars. A substantial amount. Something about the candy bar.
Anyways, I’m glad to have been of service to you all. There are now 10 known planets. You may now be productive and go about your business, whatever that is.
Clean
February 24th, 2006 at 5:12 am
Well, some very nice comments. Too bad most of them don’t make sense, for one of two reasons:
1) All objects in a system with more then two bodies do not orbit any single other object. Therefore, you can’t say “if it doesn’t orbit a star, it’s not a planet”. Nothing orbits just a star, and everything in the solar system orbits sol to some degree, or it wouldn’t be in the solar system.
2) Scientists have this thing, this very important thing, that says that the scientist isn’t important, it’s the reality that’s important. That’s why we don’t say things like “it’s not an element becuase we didn’t discover it before 1940″, or “it’s a planet because in 1950, we thought it was”. Consider that we want to use these terms to talk about planets orbiting other stars then Sol, which is why “visible with the naked eye” is a bad idea.
3) Large enough to make itself spherical is another bad idea. Earth isn’t spherical. There’s these big protrusions. We call them “mountians”. Past that, some asteroids are large enough to do so.
Really, the most important facet is that this is /science/. In science, we take in new evidence, and say “OK, we were wrong, what now”. You may have learned that Pluto was a planet, and that there are nine planets. Turns out that’s not right. Let’s figure out what is right, and start teaching it. Those who have already passed the third grade will have to deal with not everything you were taught in school being correct.
February 24th, 2006 at 6:43 am
While your other points are alright I’m afraid I have to comment on your point 1. There is in fact a rigourous, precisely defined criteria you can apply to decide whether a body is in orbit around another solar system body or not. Either the total energy of the body (kinetic – gravitational binding energy) in the inertial frame of the centre of the mass of the bodies is negative or positive. If it’s postive the body is gravitationally unbound and it is not in a periodic orbit, but if it’s negative it’s gravitational bound and will be in an elliptical orbit around the system centre of mass. So you can say unambigously whether two or more solar system bodies are orbiting each other. If they aren’t gravitationally bound to each other they’re in stellar orbits (provided they’re gravitationally bound to the star of course), and so can qualify as a planet. If they are gravitionally bound they are orbiting their mutual centre of mass, and you call all but the largest one moons, not planets.
February 24th, 2006 at 7:04 am
Point of order
Deuterium is hydrogen. So is tritium. Just because a brown dwarf doesn’t fuse the same kind of hydrogen as all of the other stars is no reason to degrade it or consider it special. You might hurt its feelings. :)
Science is about reality, and renamings are frequent. Personally, I didn’t like it when they switched from Pantera Concolor to Felis Concolor. Of course, most people just call them mountain lions or cougars.
A planet is a body which:
1. is too small to presently support fusion and did not support fusion in the past
2. Formed from a solar accretion disk
3. is large enough to be spherical under its own gravity
4. is the most massive object in its local orbital group
5. does not share a solar orbit with multiple other bodies of a similar mass that are not in its local orbital group
6. The exception to #4 is if two bodies have a roughtly similar mass and are orbiting a mutual center which is located outside of either of the two (or more) bodies. In that case, they’re both planets.
A local orbital group is defined (by me) to be a group of bodies where the radius of the bodies is within one to two orders of magnitude of the radius of the orbit. Basically, a planet and its moons or a set of mutually orbiting minor bodies.
February 24th, 2006 at 7:13 am
Karl: that’s PERFECT! We use two different names for animals (technical species name and the “lay” name), we could do the same with astronomical objects. “Planet” is the lay name. Now we need to make scientists call them something like “biggus roundus” or “hassus moonses.”
February 24th, 2006 at 7:43 am
Hmmm. There are apparently two Karls around here, but I like the way the other one thinks, so he can keep the name. ;)
Agree whole hartedly with the post.
February 24th, 2006 at 8:27 am
James makes an interesting point about some asteroids being generally spherical like Ceres. Maybe it should be reclassified as a planet. I’d be for it.
Personally I like the idea of alot of planets out there. Makes it more exciting! All these different worlds to explore and discover!
Of course in response to having all of these “Major” and “Minor” planets, we could go the Star Trek route and have a “Class M” planet or maybe something like a “Type 1″ planet and build from there.
February 24th, 2006 at 9:25 am
Some of the asteroids out there are pretty small, as well as some moons and many KBO’s, yet many are still spherical. If being spherical is the criteria, we end up with a LOT of planets.
I think the definition should be any body which gravitationally dominates the region in which it orbits. This is clearly the case with the 8 undisputed planets, and clearly not the case with Pluto and the other KBOs (though we may discover another KBO of sufficient size to do this, there’s apparently a gap where no large ones have been found).
February 24th, 2006 at 9:43 am
Sure, there are plenty of spherical bodies out there. Most fail the test.
The requirement is that the bodies are spherical [i]under the force of their own gravity. [/i]
There is a minimum size for this. I don’t know the exact numbers, but it’ll be somewhere between 100 and 1000 kilometers in diameter and depend on the composition of the body.
That means that asteroids such as Ceres do not qualify, but larger objects like Mercury, Io, and the Moon do. Of course, two of the list fail due to requirement 4.
Karl2, by request from Karl Prime
February 24th, 2006 at 10:46 am
I believe the main argument for Pluto not being a planet is the path of its orbit. The 8 inner planets all orbit in the ecliptic plane. Pluto deviates from this its orbit is tilted of the plain as if it was another type of celestial object. This plus the fact that it Pluto is outside the Kuiper Belt seems to indicate that it was not formed like the other planets of the solar system, but and instead came to be via seems some other combination of mechanisms, thus it would not be considered a planet.
February 24th, 2006 at 10:57 am
Hmm… It’s amazing how much debate the entire thing over clasifying planets has sparked.
Just my own $0.02 here, I’d have to agree with Howard’s initial comment that ther’s no way to clearly classify anything. Any time that you generate a classification it’s possible to find (or even build) something that breaks that classification (Imagine if you will a robot that performs all the defined functions of a living being, thus breaking the classification line between Organic and Inorganic)
That said, when it comes to teaching third graders about sciences in general more stress should be placed on the idea that our ideas about science are (and should be) constantly changing based on new evidence, technology and experimentation. Cirriculum that focus on memorizing outdated facts should be filed away with ideas like “Four elements” and “Flat Earths”, to be replaced with a better utilization of our modern information technology to research the state of science -now-, rather than 20 years ago.
The side benefit of that approach is the practical application of critical thinking skills. Being able to tell crackpots from genuine authorities, and being able to evaluate the ideas of authorities and crackpots alike to determine when the crackpots should be the authorities. Maybe, just maybe, a better teaching of critical thinking skills would create a better citizenry as a whole; ones that vote for politicians based on their views rather than on what party they are a part of, consumers that buy products based on their value and performance rather than marketing gimmicks.
Well, we can all dream anyway.
February 24th, 2006 at 10:57 am
“Reality is not only stranger than we imagine, it is stranger than we can imagine”
Also, bear in mind that for the majority of planets we won’t be interested enough to even name them.
February 24th, 2006 at 11:32 am
”
strangely, planet comes from a greek word meaning “wanderer.” I think we should stick with the ancient definition. the SEVEN planets are Mercury, Venus, Mars, Jupiter, Saturn, Sol, and Luna.
This definition is logically consistant, and even scientifically applicable: a planet is an object in the heavens which can be observed with the unaided eye, and appears to move on at least a daily timescale with respect to the “fixed” celestial sphere.
actually, sol could be excluded if you presume that all observations take place from the surface and require the ability to actually observe the celestial sphere and the object at the same time.
”
gosh, maybe we should go back to measuring time by sideral time while we’re at it? noon being defined as “When the sun is precisely above”?
Karl’s definition seems to work
February 24th, 2006 at 12:55 pm
I noticed a problem most have. They keep saying, “If it is larger than pluto, it is a planet. If it is smaller it is … [not]“. Lets change the the definition from pluto to mercury (which is SMALLER than pluto.)
February 24th, 2006 at 1:23 pm
Krenn.. that’s not what sidereal time is. You’ve mixed up terms there. Sidereal time is based on the celestial sphere. A sidereal day is shorter than a conventional day because the earth actually rotates through more than 360 degrees in a solar day.
The planet naming problem is this: people don’t want to change. so IAU is not only charged with creating a definiton for planet which is logically consistant, but a definition for planet which includes pluto and other 8 bodies currently called planets, excludes everything else in the solar system, and allows for the possibility of extra-solar objects to be called planets.
February 24th, 2006 at 2:14 pm
“There is a minimum size for this. I don’t know the exact numbers, but it’ll be somewhere between 100 and 1000 kilometers in diameter and depend on the composition of the body.”
True, but there’s plenty of KBOs bigger than that, and I don’t think they deserve the title “planet” either. “Planet” confers
We need some new classification for bodies large enough to gravitationally round themselves and have satellites and so forth, but that do not have the dominance to warrant a “planet” designation.
February 24th, 2006 at 4:54 pm
Isn’t “satellite” supposed to be the generic, and “Moon” refers to the Earth’s natural satellite, or has the astronomy community given up on that one as well?
February 24th, 2006 at 6:40 pm
As (almost) always, semantics….
February 24th, 2006 at 8:52 pm
Hi Everyone,
Some Comments:
Mercury is larger than Pluto.
Mercury is 4,900 km in diamter where as Pluto is 2,300 km. Ceres is 930 km.
Ceres has indeed collapsed into a sphere under its own gravity. It seems that anything with a diameter over 800 or 850 km will do so. It is likely that Ceres has undergone some geologic differentiation. (This guess is based on many meteorites have differentiated into metalic and stony parts and then have had the stony parts knocked away leaving almost pure nickle iron meteorites.)
As for Earth not being a sphere because of its equitorial bulge and mountains, that is a very minor point. If you made the Earth the size of a billiard ball, it would be rounder than any billiard ball, mountains and ocean trenches included. I think that saying that “planets are bodies that are large enough to collapse into spheres (which do not orbit other planets)” could be a reasonable criteria for judging if a body is a planet or not. Saying the Earth does not count because it REALLY isn’t a PERFECT sphere is nit picking. The major problem with that is then Ceres is a good candidate for planet hood. As for no atmosphere, when pluto is closest to the Sun, it has a thicker atmosphere than Mercury as nitrogen frost on Pluto’s surface sublimes. (Its atmosphere is still getting thicker even tho it has started moving further away from the sun as the heat from the sun continues to work its way deeper into the soil of Pluto.)
I am reluctant to call Pluto a Kuiper Belt Object because Pluto is not IN the Kuiper belt for almost all of its orbit. See:
http://www.harmsy.freeuk.com/kuiper.html
for a nice diagram showing Pluto’s orbit compared to most KBO’s.
Pluto and its moons is actually a very interesting set of objects. (Or things if you prefer.) I think it would be a shame to demote it from a planet.
Regards, Rick.
February 24th, 2006 at 10:01 pm
Well, Ceres, Pallas, Juno and Vesta have “historically” been planets. As I said, history is a stupid argument to bring to science.
That aside, Larry Niven’s “World of Ptavvs” had a marvelous if now dated take on Pluto.
And Asimov had a mystery wherein an alien referred to a ship as a asteroid. “A body moving generally in an orbit between Mars and Jupiter.”
There do have to be specific definitions to this.
Pluto’s in deep trouble. It’s not the only, the largest, or even the most important KBO. If it’s a planet, so are 50 other things going to be. If not, there won’t be a way to explain why it’s significantly different.
The only parallel even close is that the Trojan and Greek asteroids each have a few spies in the enemy camps, before the naming tradition was fixed.
But that’s got nothing to do with structure.
February 24th, 2006 at 11:25 pm
Well, I don’t know about you guys but…
Here’s an easier solution to it all. Figure out a definition of what planets, asteroids and whatnot. If people find out that X item isn’t such an item anymore, we can always ask for those same scientists to just blow the item down (or up) to the right size using whatever technology (probably a lot of atomic weapons), solving our problem of things not quite fitting.
… What, I’m a mercenary too. And I’m sure those scientists would be thrilled at the budgets in blowing things to their ‘proper’ order.
February 25th, 2006 at 8:18 am
I think a good distinction for planets would be for them to be unique objects.
Ceres though its large and round, thus wouldn’t be a planet, because its in a belt full of similar rocks.
Similarly Pluto isn’t a planet either, because there are other objects like it around.
This doesn’t mean Pluto (or those other objects) is uninteresting because its not a planet (in fact, I’m very curious as to what it really looks like up close.) Just means it ain’t a planet. I always thought it was a teeny little oddball anyway. Always sort of a planetini rather then a planet.
And now it just happens to be a KBO, and calling it a planet is just sentimental foolishness. Sold as ‘the will of the people’ (Most of the people don’t even know anything about the planets. Just ask a random person how many planets there are in the solar system. You’ll get answers ranging from five to fifteen. Let alone that they can name the order.)
February 25th, 2006 at 8:57 am
Also, the argument that Pluto isn’t quite in the Kuiper Belt isn’t valid. There are numerous asteroids not in the Main Belt, and a couple out past Saturn, not to mention the Earth and Sun grazers. They’re still asteroids.
The planets are generally categorized as terrrestrial and gaseous (or Jovian). As we discover more planets elsewhere, we’ll need to add categories. We have superJovian now, for some of those 5-50 J mass monstrosities.
But with several other similar sized masses discovered, including one larger, I think the BEST status Pluto can hope for is Kuiper Belt Planet, as opposed to Main System Planet.
Otherwise we have to argue that we’re already at 12 planets with more on the way.
There’s a similar problem counting satellites of Jupiter and Saturn. There are too danged many and most of them are temporary captures only. Interesting to study, but not really to name.
February 25th, 2006 at 10:40 am
zippthorne:
Yeah, we had Shirts vs Skins, and it was only gym class that they seperated the guys and girls, unfortunately.
February 25th, 2006 at 11:38 am
Pretty much everything has more atmosphere than Mercury. Let me put it this way:
The mean free path for particles in mercury’s “atmosphere” is significantly greater than the ballistic trajectory the particles are on. Particles are more likely to bounce of the surface than each other. This is also interesting as the collisions are pretty much perfectly elastic.
February 25th, 2006 at 12:24 pm
The Golden Age Green Lantern said:
Cerberus is a perfect name for a pluto-orbiting object, and I find it extremely fortunate that it’s not taken.
Prosperina (or Persephone) would have been my choice for the other object, but those are both taken. Is there a Dis yet?
Cerberus should be something either larger or in triplicate; the Big Dog has, after all, managed to make himself popular in disproportion to his significance in myth.
Making Prosperina/Persephone a tiny moon when she was at least a second-rank goddess does her disservice, to my mind. That’d be a better name for Charon now, but they’re not gonna juggle names because of my OCDish sense of order. *grin* (then it could be Charon and Styx, for the little ones, yeah?)
Hey! No ‘Dis’! (from here: http://cfa-www.harvard.edu/iau/lists/MPNames.html)
(1319) Disa
(15630) Disanti
(9770) Discovery
(4017) Disneya
(21999) Disora
(11037) Distler
(27977) Distratis
February 25th, 2006 at 1:05 pm
The whole problem is that Pluto is a mickey mouse planet…
February 25th, 2006 at 5:19 pm
Bit about orbits not being singular is granted. For “primarily orbits an x”, read “the most massive body the object has a fully-convex orbit around is an x”.
Yes, tertiary planets around secondary stars would be in some ways equivalent to secondary planets around single stars, but that’s indicated by sharing the designation “planet” — much like “tertiary planets” Ganymede and Titan resemble the terrestrial planets more than they resemble “tertiary asteroids” Phobos or Deimos.
And yes, it’s “complicated”, but it can be ignored by the layman. In common usage, a cucumber is a vegetable and a strawberry is a fruit, though botanical definitions would be reversed. For pedagogic purposes, the label “major planets” being limited to the nine acknowledged in 1950 would be good enough; those actually learning astronomy, like those actually learning botany, would learn the more sophisticated system. Given the current use of the term “minor planets”, this split in usage of the term “planet” already exists anyway.
On other systems:
I do like the “classical planets” approach. It’s useful. I would note that Uranus has been sighted with the naked eye, and so might qualify.
On Karl’s — the #4/#6 rules — how similar is similar? How do you define, say, a 0.47-0.35-0.23 of Jupiter mass triad where 0.35 and 0.23 are close bodies orbiting a mutual barycenter between them, and that pair and the 0.47 both additionally orbit a mutual barycenter at somewhat longer distance?
I mean, they could all be non-planets, which would seem odd for three bodies all more massive than Saturn. Or they’re all planets, despite the lightest having about a fifth of the local orbit’s mass and being less than half the size of the largest object — would it be a planet in a 0.82-0.23 system? Or 0.47 could be a planet and the others not, despite the majority of the mass not being in 0.47. Or . . . .
All systems of classification are arbitrary. The question is whether they are useful. I fail to see the utility in such an exacting definition of planet.
February 25th, 2006 at 5:40 pm
“There is no such thing as a Kuiper belt object which is not in the Kuiper belt. Duh.”
That’s like saying: There is no such thing as an American who is traveling outside the U.S.
Objects can be knocked outside the Kuiper belt. Shall we call everything in the Kuiper belt a planet once it gets knocked off course?
February 25th, 2006 at 9:14 pm
The problem is not if Pluto and the other things (“Xena and Gabrielle” or “Santa and Rudolph”) are Planets or not. The question is: do they deserve a name?. The distinction is not arbitrary, Neptune marks the boundary of the jovian planets and this distinction is important, there are only few objects (planetary subsystems) in the jovian/terrestrial dichotomy and they are distinct enough to warrant individual names.
“Plutoids” are quite likely a huge population of icy round objects that will differ essentially only on size. Having 1000 planets is not the problem, the problem is naming the damn things with names from roman gods. I wouldn’t mind defining a planet as something with a spherical shape or radius above a certain value and giving them names as Sol-IX, Sol-X, Sol XI… Sol CDLXVII, etc.. Pluto as the first detected “large” object after the jovians probably deserves to keep its name, but not the others (at least not until some humans settle there).
Of course it’s cooler saying “I discovered planet Pluto” rather than “I discovered planet Sol-IX”, but we will have to stop naming these things at some stage.
February 26th, 2006 at 12:31 am
I, for one, say that the term ‘planet’ should be a purely colloquial one. It’s a term that has been around since long before anyone had any idea what a planet actually was, and trying to force that word into having a scientific definition is like trying to hammer a square peg into a round hole… so let’s just let ‘planet’ mean whatever it will eventually come to mean through the natural evolution of language.
I can’t imagine that fixing some sort of artificial designation on what a ‘planet’ is would help out any scientists, either. Other classifications of celestial objects (“inner terrestrials,” “gas giants,” “KBOs,” “Moons of Saturn”), yes, they can be useful. But ‘planet’ just seems way too hodge-podge to actually help anybody understand anything.
February 26th, 2006 at 5:30 am
I’m not sure where the idea that Pluto isn’t a Kuiper Belt Object has come from, but it appears suprisingly popular. The Kuiper Belt is often defined as the band 30-50 AU from the Sun. Pluto has an eccentric orbit (like most KBOs) which takes it closer to the Sun than 30AU, however its mean distance from the Sun (which equals the orbit’s semi-major axis) is 39.5AU.
An alternative way of defining the extent of the Kuiper Belt, which seems to correlate well with the observed distribution of the objects themselves, is in terms of orbital periods relative to Neptune. Pluto, and approximately 150 other known KBO’s occupy orbits whose period it 3/2 times the period of Netpune. These are collectively known as plutinos and mark the inner edge of the Kuiper Belt. At the outer edge of the observed Kuiper Belt there a few tens of objects with orbital periods of twice that of Neptune (the twotinos). In between these two extremes are the remainder of the approximately 800 Kuiper Belt Objects so far observed (classical Kuiper Belt Objects). There are only a few outer solar system objects known to be closer than the plutinos or futher out than the twotinos (though some are notable, e.g. Sedna).
While Pluto is towards the inner edge of the Kuiper Belt it’s not distinct from the distribution of these objects, it has a whole load of (admittedely smaller) relatives is similar orbits. Unless being Pluto-sized is enough by itself to confer planet status Pluto is nothing special.
February 27th, 2006 at 8:32 am
I think people are missing a very important point. Someone has said before that these are SCIENTISTS doing the thinking on what is a planet, and what isn’t. But as scientists, they wont have to “just” think about OUR solar system. They need to think of other solar systems, and science as we know it is a quickly changing force.
Imagine when I was born, pluto was the 9th. planet. But when I was like what… Well, some time later anyway, scientists started finding out that there were planets around other stars… How did they know ? If there IS no clear definition of a planet, then how can they tell ? “Well, it’s there and it’s big, and we think it’s a planet”. Read the scientists reviews. Each one argues differently, but in the end, they all make valid points. Should we change the way we think because the majority says so ? If the majority said that the earth was flat, would that MAKE it so ? No, but if we change the definition of “flat”, then sure….
Now some time after that the term “free planet” was cooked up, and used to describe large objects in space that apaprently are NOT orbiting anything, but at the same time are not (or probably never have been) stars. Why would THESE objects then be categorized as planets ? I mean if they’re not even bothering to orbit a STAR, why would we think of them as planets ? Because the term “planet” is just so cool to hear ? Apparently so. The terms “other worlds”, “alien planets” and similar concoctions seems to make poeple start dreaming, and wondering. Many people would like to think that there is life on other planets (See, again the word planets, it’s fascinating, right ?). I would think that this term will eventually fall into disuse. At least I hope so.
Then what of comets, asteroids, sattelites and such ? Well, it’s not my call, but where I’m from we call a car a car, no matter if it’s a fiat, or a BMW. There are very nice definitions fitting these objects. Let’s revise those definitions if we manage to get in to trouble with them in the future (“hey I just discovered a new asteroid belt around the sun, it’s like 10 million times the size of the kuiper !”, not likely is it ?).
I will have no problem adapting to whatever the scientists cook up, and in two-three generations, people are going to loko back at this moment and wonder why it was so tough for us to decide “what is a planet”.
Tough I am no astronomer, it is my understanding that the majority of the mass in our solar system is placed in a “disk” around the sun. I would have no problem definfong a planet as the 10 largest objects created from the materials in this disc, that are currently orbiting the sun along the axis of said disc.
This would have the added benefit that ALL solar systems would have 10 planets, so you wouldn’t even have to remember how many are in each starsystem ! ;)
I would find that SO cool. But hey that’s just MY take on a difinition.
Since this wont suit people, I think the scientists will simply make it a matter of size (yes, size IS important). But wont’ make it about pluto or not…. There’s no “pluto” in the next solar system over. Simply calculate the total “weight” or mass of a solar system, and the take the previous disc orbiting definitions, and simply say any body on the disc with a mass of more than 3% of the total mass of the solar system… This would totally make the current definition valid, we’d just be replacing “significant size” with something tangible, that is still usable for solar systems with a different mass than our own…. Something our grandchildren would be happy with, I’m sure. So THEY wont have to have this argument again when they travel to the stars. (“hey is that a planet over there ?”, “Ofcourse not, you know perfectly well, planets only exist at home”).
March 18th, 2006 at 8:36 am
Personally, looking forwards to the future, a planet should be ‘anything you can’t accidently jump off because there’s too much gravity.’ With the world record highjump at less than 2.5m, http://www.iaaf.org/statistics/records/gender=M/allrecords/discipline=HJ/index.html, and v2=u2+2as http://www.gazinotes.com/a-level/M1/EQUATIONS%20OF%20MOTION.htm, the escape velocity must be less than 7m/s. By my reckoning, this means a planetoid comprised of water has to have a radius of 300km to comply.
However, it might take a while to fall back to the surface of an asteroid if you’re near the escape velocity. A lower, more practical level (ie: you come back the same hour as you left) might be more appropiate.
Dave.
November 7th, 2006 at 12:21 pm
I have rewritten the Animaniacs Planets song!
Yakko:
The closest to the sun is the planet Mercury
Next the shrouded planet Venus is as cloudy as can be
The Earth is next, we call it home, let’s hope it stays that way
And then there’s Mars, it’s really red – what more can I say?
The gassy planet Jupiter’s as big as planets come
Then there’s Saturn with its mighty rings made up of tiny crumbs
Far Uranus spins sideways but its north pole’s still on top
And Neptune’s lots of freezing gas and that is where we stop!
Wakko: I thought it was pronounced UrAYnus.
Dot: [i]Please[/i] let’s not go there.
March 25th, 2008 at 1:58 pm
Wow. So many comments that even I, procrastinating though I may be, got bored with them. Frankly, people will call things whatever. The average person doesn’t care what Pluto is, just don’t change it’s name. This whole mess is going to be an annoyance to middle school science teachers for a little while, until we get a new batch out there and they just use the debate as fodder for their lesson plans.