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MiniTES

Jul 31 2005, 05:43 PM

QUOTE (Alan Stern @ Jul 31 2005, 02:00 PM)

Localtion and relative-size arguments always have these problems. Planets are planets
because of what kind of body they are. I remain convinced it is better to pick a good
criteria-- like being rounded by gravity-- and let the number of bodies be whatever
Nature delivered.

Alan: What about Ceres and Vesta? Do you think that we should call them planets by virtue of their shape? Personally I agree with your scheme but I don't think it would be logical to call Ceres and Vesta planets instead of asteroids.

DEChengst

Jul 31 2005, 06:25 PM

QUOTE (Alan Stern @ Jul 31 2005, 04:00 PM)

Localtion and relative-size arguments always have these problems. Planets are planets because of what kind of body they are. I remain convinced it is better to pick a good criteria-- like being rounded by gravity-- and let the number of bodies be whatever Nature delivered.

Wouldn't that criteria be pretty much the same as classifying objects larger than a certain size as planets ? Afterall, to have an object pull itself into a sphere you need a certain amount of gravity. The larger the object the larger the mass and thus the force of gravity. Ofcourse if you have two objects with the same size but different density the denser object will have the bigger gravity. My guess would be that a less dense object would need less gravity to have itself pull into a spherical shape. So in the end "objects larger than x will be spherical" might still be a approximation.

BTW: With all those big KBOs being discovered, how many New Horizon missions would you like to do ?

alan

Jul 31 2005, 06:35 PM

This is how I would divide things

If it orbits a star it is a planet
If it large enough the remove or control other objects in its vicinity it is a major planet
If it is not it is a minor planet

Pluto is not large enough to remove objects near it so it is a minor planet
A Mars sized object in the Oort cloud would probably eject anything it encountered so would be a major planet

Mongo

Jul 31 2005, 06:42 PM

I think that the problem we have is that the current classification may be too coarse-grained to be all that useful at grouping objects. There will be some classification system -- the objects themselves may be unaffected by what we call them, but their perception by most humans will be affected by their classification.

What are the primary physical break-points among various sizes of objects?

1) Deturium fusion at some point in the object's history would define the upper limit of planet-hood. This is usually put at about 13 Jupiter masses.

2) An obvious break-point is whether the object was almost entirely formed from planetisimals, or whether significant direct accretion of gas also occured. Not that all 'gas giants' are the same. Jupiter and Saturn are basically solar composition, while Uranus and Neptune are depleted in H and He compared to the sun. Other planetary systems are different again. One recently announced planet is about Saturn-mass, but otherwise apparently resembles a hot Neptune.

3) Another possible dividing line is whether the object has a significant secondary atmosphere, although this has a lot to do with the level of heating from its primary -- the colder the object, the easier to retain an atmosphere, unless it's too cold.

4) Sufficient self-heating to cause significant reprocessing of the surface might be a good indicator, but it would be difficult to determine from a great distance.

5) Probably the lowest dividing line of interest is whether the object self-gravitates into a spherical shape, although again, other factors enter into this, such as composition (silicates vs ices) and temperature. Another issue would be: how spherical is spherical enough? Objects at the lower limit might be only roughly spherical, so what degree of departure from the an ideal sphere (allowing for rotation) is acceptable?

My own list of known 'major planets' would include:

CLASS 1 PLANET: (significant direct acretion of gas, no deturium fusion) Jupiter, Saturn, Neptune, Uranus

CLASS 2 PLANET: (significant secondary atmosphere, no significant direct accretion of gas) Earth, Venus, Mars, Pluto

CLASS 3 PLANET: (self-gravitates into sphere, no significant secondary atmosphere) Mercury, 2003UB313, 2005FY9, 2003EL61, Sedna, Orcus, Quaoar, Ixion, Ceres, 2002TX300, 2002AW197, 2002UX25, Varuna, 2002MS4, 2003AZ84, 2004GV9, Vesta ...

While we're at it, here is a list of moons as well:

CLASS 2 MOON: Titan, Triton

CLASS 3 MOON: Ganymede, Callisto, Io, Luna, Europa, Titania, Oberon, Rhea, Charon, Iapetus, Ariel, Umbriel, Dione, Tethys, Enceladus, Mimas, Miranda

Bill

dvandorn

Jul 31 2005, 07:44 PM

If real estate doesn't matter and you classify planet vs. non-planet based solely on size and mass (i.e., is it big enough to have pulled itself into a ball), then what about a majority of the moons of the gas giants? Remember, real estate cannot be a factor in the equation.

Under the classification system that everything massive or large enough to pull itself into a sphere (more or less) is a planet, we have to admit Ceres, Vesta, the Galilean moons of Jupiter, many other Jovian moons, a lot of Saturnian moons, a lot of Uranian and Neptunian moons, plus possibly thousands of KBOs, all into the League of Planets.

Oh, and while it's not usually called a planet, our own Moon would have to be considered a planet, too.

If you're going to make an exception for bodies that orbit other planets to call them moons, then you're allowing real estate to enter the equation, and once you do that, you're simply applying arbitrary dividing lines...

-the other Doug

Alan Stern

Jul 31 2005, 08:07 PM

I do think Ceres is a planet: a dwarf one, but no less a planet than a 100 Mj object
is a star.

I wrestled with this whole question a long time ago, and I think the fundamental
difference between a planet a a big rock is that a planet does something collectively--
i./e., it shapes itself into a sphere by graivty overcoming maerial strength. Anything
too small to do this is acting like a rock. Anything beig enough to do this, but
not so big that it does fusion, is a planet.

And as I point out in public talks sometimes, though many, amny adults claiim
to have never thought about this, any kid knows it: jst ask a kid to draw
a planet; they always draw a circle, never an egg or a box or a pyramid or
even a hamburger. Kids know planets are things that are essentially spherical;
of course most don't know why this is so, but they recognize the observational
telltale, that's for sure.

-Alan

Alan Stern

Jul 31 2005, 08:11 PM

[quote=alan,Jul 31 2005, 06:35 PM]
This is how I would divide things

If it orbits a star it is a planet
If it large enough the remove or control other objects in its vicinity it is a major planet
If it is not it is a minor planet

...Careful, stars orbit stars.

As to Pluto etc. being "minor" planets, I agree in spririt but prefer
the term "dwarf" planet for two reasons. Firstly, this is a well accepted
terminology in astrophysics (i.e., there are no minor stars or galaxies,
but there sure are dwarf stars and dwarf galaxies). And secondly,
some scientists say they feel that the term "minor" is pejorative in that
one who works on "minor" object is not doing something as important as one
might. I personally don't feel this way, but I am sensitive to the many
people who do.

Alan Stern

Jul 31 2005, 08:14 PM

QUOTE (Mongo @ Jul 31 2005, 06:42 PM)

I think that the problem we have is that the current classification may be too coarse-grained to be all that useful at grouping objects. There will be some classification system -- the objects themselves may be unaffected by what we call them, but their perception by most humans will be affected by their classification.

What are the primary physical break-points among various sizes of objects?

1) Deturium fusion at some point in the object's history would define the upper limit of planet-hood. This is usually put at about 13 Jupiter masses.

2) An obvious break-point is whether the object was almost entirely formed from planetisimals, or whether significant direct accretion of gas also occured. Not that all 'gas giants' are the same. Jupiter and Saturn are basically solar composition, while Uranus and Neptune are depleted in H and He compared to the sun. Other planetary systems are different again. One recently announced planet is about Saturn-mass, but otherwise apparently resembles a hot Neptune.

3) Another possible dividing line is whether the object has a significant secondary atmosphere, although this has a lot to do with the level of heating from its primary -- the colder the object, the easier to retain an atmosphere, unless it's too cold.

4) Sufficient self-heating to cause significant reprocessing of the surface might be a good indicator, but it would be difficult to determine from a great distance.

5) Probably the lowest dividing line of interest is whether the object self-gravitates into a spherical shape, although again, other factors enter into this, such as composition (silicates vs ices) and temperature. Another issue would be: how spherical is spherical enough? Objects at the lower limit might be only roughly spherical, so what degree of departure from the an ideal sphere (allowing for rotation) is acceptable?

My own list of known 'major planets' would include:

CLASS 1 PLANET: (significant direct acretion of gas, no deturium fusion) Jupiter, Saturn, Neptune, Uranus

CLASS 2 PLANET: (significant secondary atmosphere, no significant direct accretion of gas) Earth, Venus, Mars, Pluto

CLASS 3 PLANET: (self-gravitates into sphere, no significant secondary atmosphere) Mercury, 2003UB313, 2005FY9, 2003EL61, Sedna, Orcus, Quaoar, Ixion, Ceres, 2002TX300, 2002AW197, 2002UX25, Varuna, 2002MS4, 2003AZ84, 2004GV9, Vesta ...

While we're at it, here is a list of moons as well:

CLASS 2 MOON: Titan, Triton

This sounds pretty good! The one comment I'll make here is that we have been
carefful not to insist that an object BE spherical, only that it be massive enough
to become spherical. This avoids issues like the one you brought up (who
spherical does it have to be?), as well as issues related to rotational
flattening (ala Jupiter and Earth).

CLASS 3 MOON: Ganymede, Callisto, Io, Luna, Europa, Titania, Oberon, Rhea, Charon, Iapetus, Ariel, Umbriel, Dione, Tethys, Enceladus, Mimas, Miranda

Bill

dvandorn

Jul 31 2005, 08:15 PM

So, is Titan a planet? Is Ganymede? Is Triton?

Or does real estate count, after all?

-the other Doug

Alan Stern

Jul 31 2005, 08:16 PM

QUOTE (dvandorn @ Jul 31 2005, 07:44 PM)

We dealt with the satellites issue in a long IAU article which I am happy to share if
anyone wants it; just email me and I'll send it.

Here's what we said: if an object fitting the planetary definition orbits another planet
then it is called a satellite of the planet and a "planetary body", but not a planet.

dvandorn

Jul 31 2005, 08:29 PM

OK -- fair enough. Though that *is* allowing a gravitational definition of real estate to affect the terminology...

Isn't there some theory out there that Triton was once a KBO that was later captured by Neptune? If that's the case, then you would say that Triton is a planetary body that was once a planet but is now a satellite?

I think the reason people are so energized over the classification issue is that most people have a need for a world around them that they can hold in their heads at one time. When we think of a city, for example, we think in sequential sequences of roughly ten-square-block areas that we can characterize in our minds "at once." We even give names to these small, handle-able chunks, calling them districts or neighborhoods. But we chop things into segments that we feel comfortable dealing with as single entities.

If you want people to feel like they have a place in a larger Universe, you need to give them relatively "small" chunks to deal with. Giving school kids ever-widening chunks (Earth as a planet, Earth/Moon System, Inner Solar System, Solar System) you keep the number of elements of each "chunk" under 10. That seems to be a good limit, since anything that gets a lot more complex is difficult for an average person to handle in one "chunk."

So, I think it is important to give people some kind of system that identifies a Solar System consisting of a number of objects (in the vicinty of 10 or so objects) that they can grasp in one "chunk." When you add thousands of objects, you need to add them "en masse," is with the Asteroid Belt, the Kuiper Belt, the Oort Cloud -- note that those are all singular, not plural, nounds. Otherwise, people begin to feel lost and overwhelmed by the sheer number of "things" they need to consider or account for within a given system.

(Note -- I'm not talking about the scientists and engineers, here, who are trained, or have an affinity, to think in different scales. I'm talking about your normal, salt-of-the-Earth kinds of people who make up 95% of the world's population...)

-the other Doug

DEChengst

Jul 31 2005, 08:40 PM

QUOTE (Alan Stern @ Jul 31 2005, 10:07 PM)

Just ask a kid to draw
a planet; they always draw a circle, never an egg or a box or a pyramid or
even a hamburger.

I bet Borg children would draw a box

Alan Stern

Jul 31 2005, 09:19 PM

Other Doug-- I respectfully disagree; people I speak to in public talks find the i
dea of there being a lot of planets new and captivating, many even find it really
enchanting.

I don't think they have any problem at all getting used to lots of planets as long
as they know that, like stars, they won't have ot be able to name them all.

-Alan

ps. Yes, Triton's retrograde orbit means it is a capture from heliocentric orbit. It
formed as a planet and was captured to become a satellite. Because it orbits
a planet now, rather than old Sol, it is best to refer to this kind of object as
a planetary body or a planetary-scale satellite. If you do look at the Icarus
paper reference I sent a yesterday, you will see that Triton is hard to capture,
indicating that indicates there were a lot of them once around in the U-N zone,
in order to get one into orbit around Neptune.

dilo

Jul 31 2005, 10:13 PM

Alan, you observed that my scheme wouldn't correctly classify eventual Mars-sized objects in the Oort Cloud or ejected Earth-sized bodies...
Maybe, but the constraint I made in terms of orbit and population sizes goes in the same direction of your criteria: "If is large enough the remove or control other objects in its vicinity it is a major planet", otherwise is a minor planet. I must admit that latter criteria is simpler and less arbitrary, but mass treshold would be harder to calculate, because depends on distance from the Sun...
If joined to the spherical shape constraint, this criteria appear acceptable (I wouldn't classify as a planet an isolated chunck of rock orbiting the Sun!)...
Based on this, I'm happy for the satellite statement too: "if an object fitting the planetary definition orbits another planet then it is called a satellite"; now, if "planetary definition" includes also constraint on size/shape, IAU shold update the list of planets orbiting giant planets or, at least, divide them in the two cathegories of major and minor/dwarf satellites!

Mongo

Jul 31 2005, 10:33 PM

Just to let everybody know ... there is a new Yahoo Group called 'majororminor' located here, concerned with discussing the definition of a planet, and related topics. I have already posted some of my earlier posts from this forum there, but thought it would be good to have multiple viewpoints from outside the mpml community.

Bill

p.s. Is it okay for flog this new site here?

BruceMoomaw

Aug 1 2005, 03:31 AM

Alan Stern: "The one comment I'll make here is that we have been
careful not to insist that an object BE spherical, only that it be massive enough
to become spherical. This avoids issues like the one you brought up (who
spherical does it have to be?), as well as issues related to rotational
flattening (ala Jupiter and Earth)."

Ah, but whether an object is "massive enough to become spherical" depends on what kind of substance it's made of, and thus how rigid it is. And determining that is a lot more difficult than determining how spherical it actually is.

Moreover, we once again have the problem of fuzzy borders. Pallas (which Mongo accidentally left off his list of Class 3 planets) and Vesta are mildly but significantly non-spherical, and NOT because of rotational flattening. Among the moons, so are Iapetus and Mimas -- to say nothing of Neptune's second-biggest moon Proteus, which looks like nothing so much as a giant marshmallow. And given the number of KBOs, there are bound to be a lot of them that fall into this "Is it spherical or not?" category.

Parenthetically, has anyone come up with a convincing explanation for why Pallas -- alone of all significantly large asteroids -- has that incredible 30-degree orbital tilt? Either something really big ran into it (in which case one would tend to think its parent body would have shattered into multiple objects), or something even bigger brushed past it and tidally yanked it into that orbit.

BruceMoomaw

Aug 1 2005, 03:33 AM

More news from Mike Brown via Ron Baalke in the "Planetary Sciences" webgroup: the Spitzer Telescope's IR observations of 2005 FY9 show it to be only 50-75% of Pluto's diameter -- which takes it off the "planet" list even if one defines a planet as something more than 2000 km wide. So we're back to 10.

Decepticon

Aug 1 2005, 03:42 AM

Boy would I love to see one of these up close.

Makes you wonder if all stars in the Milky Way have KBO.

Rob Pinnegar

Aug 1 2005, 05:57 AM

Forgetting about trans-Neptunian objects for the moment: I'm going to play Devil's advocate here...

If I recall correctly, the millenia-old original list of "planets" included seven objects: the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn.

Since that list was defined, we have been finding ways of updating it by redefining the word "planet" in ways that incorporate new discoveries while conveniently keeping most of the original members on the list. But even if we only consider the "Mercury-through-Neptune" list, we hit some problems.

Does it really make sense to put Saturn and Mercury in the same taxonomic classification, when one of them is two thousand times more massive than the other, and their compositions are completely different?

On the same note, is Jupiter a planet in the same way that Mars is a planet?

Some people call the Earth-Moon system a "double planet" -- so why don't we cut Neptune and Triton the same slack? Or Saturn and Titan? And why isn't the Jupiter system called a "quintuple planet"?

If we are going to consider demoting Pluto from planetary status, then maybe it's time to throw out the baby with the bathwater, and demote _everything_ from planetary status, because "planetary status" has become a quaintly outmoded concept. We need to divorce ourselves from our sentimental attachment to the word "planet". Five thousand years ago, it meant something, but not any more. It is obsolete.

Pluto is what it is, no matter what we call it.

Cheers
Rob, Canada

abalone

Aug 1 2005, 06:23 AM

QUOTE (BruceMoomaw @ Aug 1 2005, 02:31 PM)

The chondrules that make up carbonaceous chondrites what about them?

"A roughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at about 1400°C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5 to 2 mm in diameter and are usually composed of iron, aluminum, or magnesium silicates in the form of the minerals olivine and pyroxene, with smaller amounts of glass and iron-nickel. Together with calcium aluminium inclusions, which predate them by a couple of million years, they are among the oldest objects in the Solar System with an age of about 4.57 billion years. They formed when dusty regions of the solar nebula were heated to very high temperatures, became molten, and then resolidified as tiny droplets. "
From http://www.daviddarling.info/index.html

Were they all once planets and are there enough combinations of letters to name them all if they were?

This shows the pointlessness of trying to invent rules where none are needed.

Alan Stern

Aug 1 2005, 06:40 AM

Chonrules are spherical due to surface tension, not gravity. It's not that
an object *is* spherical, the thing that counts, that reveals it acts like a planet in
a fundamental way, is that it is massive enough to have its shape controlled
by self-gravity.

abalone

Aug 1 2005, 07:00 AM

QUOTE (Alan Stern @ Aug 1 2005, 05:40 PM)

Chonrules are spherical due to surface tension, not gravity.

I realise this Alan, I was just taking the rule to its ultimate extreme. Exactly how big would it have to be before gravity is stronger than surface tension, 10m, 50m certainly by 100m?
If there was a material that had no surface tension then gravity would cicularise it irrespective of mass and if a 100km lump of rock had enough internal heat generated by short lived radionucleides it would melt and form a sphere due to gravitational forces in the brief time before it resolidified, but now I am getting ridiculous again

It is like making up a rule for what constitutes a tall or a rich person

dvandorn

Aug 1 2005, 07:37 AM

I've been enjoying the discussion, actually. It's obvious that human beings need to classify things into systems -- it's how we look at things. And whenever you get into defining rules for systems, you get into such wonderful discussions as this...

Alan, believe me when I say that I respect your opinion and your accomplishments. Quite a bit. I've also enjoyed how you have stuck to a single set of referents within the argument, no matter how many people have tried to place their own rules onto the system.

I still think there need to be more useful and handle-able subclassifications within the system for "popular consumption." But other than that, your logic holds sway, Alan.

-the other Doug

BruceMoomaw

Aug 1 2005, 09:03 AM

Today's MPEC ( http://cfa-www.harvard.edu/mpec/K05/K05P01.html ) knocks the absolute magnitude of 2005 FY9 down to 0.3 (as against 0.4 for 2003 EL61 and minus 1.2 for 2003 UB313).

edstrick

Aug 1 2005, 10:14 AM

I haven't read every work exhaustively in the "planet definition" discussion, but there's one idea I've had for some time that seems to cut to the core of the distinction between planet and "minor body".

As planetismals form in scenarious of planet, asteroid and comet formation, they grow by hierarchial capture of smaller objects, so that at any time there's a few relative big ones, lot's of relative small ones, and Sagans (billions and billions) of tiny ones. But initially, they the big fish all eat the little fish by simply running into them. Their cross-section for capture is simply their projected surface area.

As the biggest planetismals grow bigger, they start to get significant gravity. At whatever the average local encounter velocity is for that part of the nebula at that time, eventually their gravity bends approaching objects in toward collision and accretion. As that threshold is passed, the cross-sectional capture area becomes larger, then much larger than the purely geometric area.

At that point, a vaccuum-cleaner effect starts to become significant, and the biggest fish start eating faster and faster, as you start to get almost a run-away accretion. (True runaway accretion is what's proposed to happen around a 25 or so earth-mass core when a proto-gas-giant starts sucking hydrogen and helium in a purely hydronamic infall)

My proposal is a planetismal becomes a planet when it's capture area is some somewhat arbitrary times larger than it's cross-sectional area. The asteroid belt and Kuiper belt seem have to have the largest objects get up to or slightly above this threshold.

I don't know whether models show a distinct break in the size-frequency distribution of objects on a log-log plot that's related to incresed gravitational cross section. That break in the curve would be the division point for any segment of the solar system to decide between planet and planetisimal.

abalone

Aug 1 2005, 12:28 PM

QUOTE (dvandorn @ Aug 1 2005, 07:29 AM)

OK --
If you want people to feel like they have a place in a larger Universe, you need to give them relatively "small" chunks to deal with. Giving school kids ever-widening chunks (Earth as a planet, Earth/Moon System, Inner Solar System, Solar System) you keep the number of elements of each "chunk" under 10. That seems to be a good limit, since anything that gets a lot more complex is difficult for an average person to handle in one "chunk."

So, I think it is important to give people some kind of system that identifies a Solar System consisting of a number of objects (in the vicinty of 10 or so objects) that they can grasp in one "chunk."
-the other Doug

I think I agree more with Alan S that if you want to give people a taste of the enormity and vastness of the universe, to challenge their povincial view and give them a feel for our place in it, the more planets the better, so lets be generous and not limit ourselves to a 19 century perspective. It is often difficult for us to make a quantum leap and accept that reality is no longer represented our old neat picture of the solar system.

In teaching basic astronomy to students I find it difficult even to give them a rudimentary understanding of say the enormous distance to the nearest star with respect to the size of our solar system and how this makes the prospect that we have been visited by aliens so unlikely. Lets not hide the truth, a solar system is a lot more interesting the a few planets and moons.

abalone

Aug 1 2005, 12:38 PM

QUOTE (dvandorn @ Aug 1 2005, 06:37 PM)

It's obvious that human beings need to classify things into systems
-the other Doug

Classification is a good and noble scientific cause but the group of bodies orbiting our sun that we call planets dont have a lot in common. Any classification system that puts Jupiter in the same group as say Mars or Mercury is not really of any scientific relevance and more for lay media consumption. It would be difficult to convince me that Mars has more in common with Jupiter than it has with Pluto.

AndyG

Aug 1 2005, 03:11 PM

QUOTE (abalone @ Aug 1 2005, 12:38 PM)

Absolutely! The only time that Mars and Jupiter really had anything in common was in the eyes of pre-telescopic ancient cultures. Planets - πλανήτης - "wanderers". Not a bad description a few thousand years ago, but really rather redundant today, especially for new-found planets that require 30cm+ scopes to even see...

Cast Pluto into the KBO bin, I say! There's 4 gas giants and 4 terrestrial planets. Everything else can be organised by groupings: asteroids, comets, satellites, etc.

Andy G

ilbasso

Aug 1 2005, 04:24 PM

Our taxonomic system for life went through some major changes once we discovered how to use nuclear and mitochondrial DNA to map the evolution of species. Some beings that "clearly" fell into one category and thought to be related to others, that on the surface apepared to be similar, are now thought to be completely different.

Is there a similar way in which we might classify stars/planets instead by how they evolved? E.g., are they primarily plasma, gaseous, rocky, or icy? Or do they have molten cores or not?

dvandorn

Aug 1 2005, 05:48 PM

Don't delude yourselves, guys -- there is a far larger percentage of the world's population out there who are terrified by the increasing complexity we can now see in the Universe, than are awe-struck and delighted.

One of the reasons so many people in this world retreat into incredibly narrow and limiting, but very well-defined, roles and world-views is because facing up to how complex the world *really* is scares the living daylights out of them.

Since scientists and like-minded individuals rarely, if ever, have to deal with those people in any context other than the extremely mundane, we tend to forget that they're out there. But they are, and they outnumber us hundreds to one. (Note that you'll rarely see one of these people at a lecture by an astrophysicist -- except perhaps to demonstrate against the "relentless march of science" as if it's a bad thing, or loudly proclaim that "your science is all false becasue my god told me so." Just Google up some discussions about Creationism and its teaching in American public schools, if you don't believe me.)

Not that we need, as a culture or as individuals, to hide from the ever-more-complex Universe that is unfolding before us. Just that we need to understand that a vast majority of the human populace is irrational and fears this trend towards complexity-beyond-their-ability-to-understand, and that we need to take that at least somewhat into account when we design classification systems.

(Of course, there is always that relatively small percentage of scientists who *glory* in making their classification systems as complex and unapproachable as possible, so that the average person out there will confuse the system with magic, and confuse the scientist with a magician... but those ego-maniacal scientests tend to be few and far between. I think most of them work for ESA, though... *sigh*...)

-the other Doug

JRehling

Aug 1 2005, 08:44 PM

QUOTE (BruceMoomaw @ Jul 30 2005, 10:55 PM)

In our little private "Planetary Sciences" webgroup, Ron Baalke quoted Mike Brown himself as saying yesterday: "Based on Spitzer measurements, 2005 FY9 is confirmed to be smaller than Pluto." Unfortunately, he didn't say how much smaller. But at any rate the Revolution is now upon us: depending upon what size you use as a dividing line, the Solar System no longer has 9 known planets. It now has 10 or 11, or else it has 8, or else (if you follow Alan Stern's lead) it has a hell of a lot more. What we are really going to have to tell the schoolkids, of course, is that the question from now on will be forever ambiguous.

If I were designing a roster of solar system entities for fifth grade classrooms for the 2006-7 school year, I would have it read something like this:
Sun, Mercury, Venus, Earth, Mars, asteroids, Jupiter, Saturn, Uranus, Neptune, Pluto, [Whatever name 2003 UB313 ends up getting], comets, Kuiper Belt. (Yes that list ends up sounding like the roster of Santa's reindeers, which might be a nice way to get kids to remember some of it.)

If the number of things of planetlike size gets to be much bigger, it will start to be cruel to expect wee little kids to remember them all, which may merit dropping individual mention of everything past Neptune -- that's not a scientific measure, but a pedagogical one.

tedstryk

Aug 1 2005, 11:50 PM

QUOTE (JRehling @ Aug 1 2005, 08:44 PM)

In the case that too many planets are found, It might be useful to retain a name like Kuiper belt, and teach that it contains lots of asteroids, comets, and planets. So there could be the Mercury - Neptune sequence, and then the "Objects of the Kuiper Belt."

spaceffm

Aug 2 2005, 12:19 AM

For all interested in sizes i made 2 little Diagramms.
The First contains earth, some moons, biggest planetoids, some tno ect.

All sizes of all shown bodies are correct and in the same scale to each other as far as known.
Of course there it is not made public a definite diameter of 2003 UB313, 2005 FY9 und 2003 EL61 ( +b ).
2003 UB313 has a diameter of 2800km ( latest status ) in my graphic.
2005 FY9 has 1600km, 2003 EL61 has 1500 km with b aprx. 250km.

The 2nd graphic shows the first together with Jupiter...

Normal
used without credt so editid out,,, too bad

Before using it somewhere else please ask and give credit, i worked 6 hours in total time...Puh...thx

How small Enceladus is, but so activ...
So size does not always matter...

gpurcell

Aug 2 2005, 01:20 AM

At what mass will a body have a differentiated core?

Rob Pinnegar

Aug 2 2005, 01:23 AM

QUOTE (dvandorn @ Aug 1 2005, 11:48 AM)

One of the reasons so many people in this world retreat into incredibly narrow and limiting, but very well-defined, roles and world-views is because facing up to how complex the world *really* is scares the living daylights out of them.

I guess that pretty much sums up people like Moon Hoaxers. If you're going to believe that astronauts landed on the Moon, you have to accept that there were (and still are) large numbers of engineers and scientists out there who were smart enough to figure out how to do it. For some reason that makes certain people feel small. It's easier for them to believe that it was all made up.

tedstryk

Aug 2 2005, 01:31 AM

It might be cool to add Ganymede, since it is the largest moon, and Europa, since it is such a hot topic. Great graphic!

ilbasso

Aug 2 2005, 02:19 AM

And don't forget Venus! (I know, and Saturn, and Uranus, and Neptune...)

I agree, cool graphic!!! Thanks for posting it!

Decepticon

Aug 2 2005, 03:54 AM

That is a Great chart!

Very few of those on the net. And the ones that are out there are not updated.

abalone

Aug 2 2005, 09:24 AM

Here's something to consider

Brown argues that astronomers cannot control what gets called a planet. "Our culture has fully embraced the idea that Pluto is a planet and scientists have for the most part not yet fully realized that the term 'planet' no longer belongs to them," he says.
"Everyone should ignore the distracting debates of the scientists, and planets in our Solar System should be defined not by some attempt at forcing a scientific definition on a thousands-of-years-old cultural term, but by simply embracing culture," says Brown. "Pluto is a planet because culture says it is." And, he adds, that means his new find is a planet too.
http://www.nature.com/news/2005/050801/full/050801-2.html

Benoît

Aug 2 2005, 10:05 AM

QUOTE (abalone @ Aug 2 2005, 05:24 AM)

There was a time when culture said the earth is the centre of the universe and the sun as everything else rotates around it. That cultural icon was challenged by science with a nice mesure of success.

It would be a shame to let culture intimidate science.

paxdan

Aug 2 2005, 12:03 PM

QUOTE (spaceffm @ Aug 2 2005, 01:19 AM)

For all interested in sizes i made 2 little Diagramms.
The First contains earth, some moons, biggest planetoids, some tno ect.

All sizes of all shown bodies are correct and in the same scale to each other as far as known.
Of course there it is not made public a definite diameter of 2003 UB313, 2005 FY9 und 2003 EL61 ( +b ).
2003 UB313 has a diameter of 2800km ( latest status ) in my graphic.
2005 FY9 has 1600km, 2003 EL61 has 1500 km with b aprx. 250km.

How small Enceladus is, but so activ...
So size does not always matter...

Nice one, err how about including a single pixel width yellow curved line to indicate the size of the sun for comparrison too.

abalone

Aug 2 2005, 12:12 PM

QUOTE (Benoît @ Aug 2 2005, 09:05 PM)

Good try but not the same. In your example scientific discovery was totally in conflict with the established culture. The two were mutually exclusive.

With planets it is only a slightly different interprtation between "culture" and a group of astronomers who cant even present a uniform position in scientific literature.

I am not sure that the population at large would be convinced that the Earth is not the centre of the universe and the sun as everything else rotates around it, if half the scientific community was telling them it is.

ljk4-1

Aug 2 2005, 02:00 PM

QUOTE (paxdan @ Aug 2 2005, 07:03 AM)

Nice one, err how about including a single pixel width yellow curved line to indicate the size of the sun for comparrison too.

And don't forget how active Triton is. Maybe it's just thanks to Neptune, but it makes one wonder what is going on in the Pluto-Charon system.

odave

Aug 2 2005, 02:23 PM

QUOTE (JRehling @ Aug 1 2005, 04:44 PM)

If I were designing a roster of solar system entities for fifth grade classrooms for the 2006-7 school year...

One thing I've discovered about elementary age kids, after doing astronomy nights and LEGO robotics with them, is that they are a lot smarter and more sophisticated than many adults give them credit for. And they really seem to appreciate an adult giving them an honest "we don't know for sure" answer.

So I'd give them JRehling's curriculum through Neptune and then "take the bull by the horns" with them on Pluto and KBOs. I'd explain the reasoning behind both sides of the planet/not planet debate, then ask them what they thought. It would be a great exercise in observation, logic, reasoning, testing hypotheses, and debate. From what I know of fifth graders, they can certainly handle the ambiguity and would delight in knowing that their opinion is as good as anyone else's.

Rob Pinnegar

Aug 2 2005, 02:30 PM

QUOTE (abalone @ Aug 2 2005, 03:24 AM)

"Everyone should ignore the distracting debates of the scientists, and planets in our Solar System should be defined not by some attempt at forcing a scientific definition on a thousands-of-years-old cultural term, but by simply embracing culture," says Brown. "Pluto is a planet because culture says it is." And, he adds, that means his new find is a planet too.

That's a terrible argument. It would make astronomy one big Appeal to Popularity.

A hundred years ago, a paleontologist discovered and described a dinosaur he christened "Apatosaurus". His work was ignored. Just after that, somebody else found another skeleton of the same dinosaur and named it "Brontosaurus". For a century, in the public mind, "Brontosaurus" was synonymous with "dinosaur".

Then somebody ran across the original discovery, and made people aware of it. The paleo community immediately changed the name to Apatosaurus. Why? Because the first discoverer gets naming priority, and they weren't about to change the rules to accomodate Joe Sixpack's idea of what a dinosaur should be called.

If astronomers are going to "embrace culture", then they'd better be ready to call themselves "astrologers", learn to read horoscopes, and accept people like Hoagland into their ranks. I agree that it's bad form to unnecessarily confuse the public -- but if it's necessary, then do it. Let's face it, they're going to be confused most of the time anyways.

Myran

Aug 2 2005, 02:37 PM

QUOTE

ljk4-1 said: And don't forget how active Triton is. Maybe it's just thanks to Neptune, but it makes one wonder what is going on in the Pluto-Charon system.

Neptune have a mass just so many times larger than Triton, and Tritons orbit are retrogade and eccentric - so theres some energy getting pumped into Tritons interior by constant flexing.

Pluto and Charon are -comparatively speaking- almost of the same mass, in addition it is thought that they always show the same face against each other.

So the tidal flexing will be quite limited, but there are some other things we might find thats unique. It have been speculated that Pluto and Charon might exchange a bit of Plutos thin atmosphere. Yet it have started to freeze as Pluto moves away frmo the sun and when New Horizons get there it might be so thin that we might not be able to find if that truly occurs.

centsworth_II

Aug 2 2005, 03:23 PM

Rather than embracing culture, why not embrace history? The nine original planets can be focused on in an historical context the same way the the thirteen original colonies enjoy a special place in american history. The discovery of additional planetary objects opens a new era in the study of the solar system and these objects are separated historically as well as spacially from the original nine. I see no problem with "The NIne" maintaining a special place no matter how many other planetary objects are discovered orbiting our sun.

JRehling

Aug 2 2005, 03:23 PM

QUOTE (odave @ Aug 2 2005, 07:23 AM)

Honest question: Is that a random sample of all kids that age, or are those the ones who choose to show up for astronomy night and LEGO robotics? It's a wide bell curve. With ability not the only independent variable.

Your proposed discussion does sound good, though.

ljk4-1

Aug 2 2005, 03:37 PM

QUOTE (JRehling @ Aug 2 2005, 10:23 AM)

I sometimes volunteer at the local observatory on their open house nights. When Mars was at its closest in 2003 (the real close encounter

, I recall that one of the few people who really seemed to know what was going on (at least out loud) was a 4-year-old boy.

To top it off, when I asked him what he thought made the Red Planet red (I know, it doesn't look red in the telescope, but never mind here), he suggested the lava from the volcanoes there. I got the impression that his parents and others around him didn't even know Mars had volcanoes, let alone even bother to speculate as to why the planet's surface looks as it does.

I just hope his intelligence and sense of wonder isn't totally destroyed by our so-called educational system.

JRehling

Aug 2 2005, 03:41 PM

QUOTE (Rob Pinnegar @ Aug 2 2005, 07:30 AM)

That's a terrible argument. It would make astronomy one big Appeal to Popularity.

[...]

If astronomers are going to "embrace culture", then they'd better be ready to call themselves "astrologers", learn to read horoscopes, and accept people like Hoagland into their ranks. I agree that it's bad form to unnecessarily confuse the public -- but if it's necessary, then do it. Let's face it, they're going to be confused most of the time anyways.

One thing I'd like to add is that we should remember what topic astronomers are experts on. (Or, let's say, planetary scientists.) They know scads about how worlds evolve, what sort of dynamic properties ruled them in the past and continue to rule them in the present. They are very familiar with the bulk and trace properties of the worlds in our solar system. That doesn't mean they are particularly skilled at taxonomizing, categorizing, naming, etc., even though they have the facts at hand that a taxonomist would make use of.

I heartily recommend George Lakoff's narrative in his book "Women, Fire, and Dangerous Things" concerning a debate in biology over taxonomies (and biologists are presumably much more practiced in taxonomy than astronomers!). Perhaps by being so close to the subject matter, the biologists seem to have missed some essential points -- in my opinion, Lakoff, a linguist who is undoubtedly farther from the biological facts, cuts the Gordian knot at the center of the debate, identifying it as not really a debate at all.

Astronomy circa 1959 had an easy time of it. There were 9 known things Mercury sized or bigger (Pluto was supposed to be that size); uncounted stars, each far bigger than Jupiter; a collection of smaller asteroids, none more than a fraction of Mercury's diameter; and dozens of natural planetary satellites, in no case within a factor of 80 of the mass of its primary. The only bumps in the road were that 2 or 3 satellites of giant planets were bigger than Mercury, and that the whole comet-asteroid distinction was a bit puzzling. But overall, I would say that professional astronomers were less acquainted -- needed less to be acquainted -- with tough taxonomical decisions than did a baker, a mapmaker, or a bricklayer. When the time has come that some tough decisions confront the field, there's no reason to suppose that the inside people with the facts will easily and triumphantly rise to the occasion because they have the facts -- it's quite easy to find a way to get tripped up in the facts, uncertain of what to cling to when the easy categorizations fail.

In short, I'm not sure if a room of astronomers with votes to cast would do a good job settling this if they had to vote off the cuff. I have a better feeling that with some good discussion, those who have better things to say about it will get to sway the mass of astronomers and come up with something that will filter well through elementary school teachers and journalists and end up being a way to describe our corner of the universe in a way that makes it accessible for as many people as possible.

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