Pluto on the Bubble

[EHocking]

Just for the sake of amusement, could you give a "reasonable definition" of a planet that isn't arbitrary?

Also, can you define the difference between a hill and a mountain?

One inch?

Probably less...

 

[Dark Jaguar]

Not sure why people are making a big deal out of this, for reasons already listed it's been arbitrary for some time, and I aims to keep it that way!

As for the cartoon dog question, what's to wonder about? Why can humans speak but monkeys can't? We're different creatures! Or, for the more pragmatic answer that solves everything in all fiction, "it was in the script".

 

[Starthinker]

On a slightly related note I did learn today that a rock is undisturbed and in it's natural state and becomes a stone once it's moved by artificial means. This is why we have stone houses (not rock houses) and stonehenge. So, the gravel in your driveway is made of stones, but that thing by the tree in the woods is a rock. Gemstone on your finger. Rock of Gibralter. It seems logical.

At least, that's what I heard. I'm too tired right now to look it up.

 

[Johnny Pixels]

On a slightly related note I did learn today that a rock is undisturbed and in it's natural state and becomes a stone once it's moved by artificial means. This is why we have stone houses (not rock houses) and stonehenge. So, the gravel in your driveway is made of stones, but that thing by the tree in the woods is a rock. Gemstone on your finger. Rock of Gibralter. It seems logical.

At least, that's what I heard. I'm too tired right now to look it up.

Ooh that's cool, I never knew that.

Works with the Rolling Stones too.

What about a rock garden/rockery though?

 

[Dragon]

Ooh that's cool, I never knew that.

Works with the Rolling Stones too.

What about a rock garden/rockery though?

Well, a rock garden is supposed to be imitating natural formations, so it's sort of poetic licence.

 

[ponderingturtle]

If we get rid of Pluto, who will I know what My Very Eager Mother Just Served Us?

This is all very silly, in my opinion. This is not a scientific debate. Adding or removing Pluto from the list of planets does nothing to further our understanding or knowledge of the universe. It is important to know that there's this rock out beyond Neptune (most of the time) that orbits the Sun. Whether we call it a planet or not matters very little. I'm calling it "Bob".

But we added ceres, so you need to have something with C inbetween M and J on there now anyway.

Think of all the trivia questions that have been messed up by this.

 

[Molinaro]

Er, probably not, because there's no other option for a configuration of stars.

I may not be fully understanding your question.

Only smaller bodies -- planets and such-like -- have been observed to arrange themselves in satellite-like configurations, where body A orbits body B, while the joint A-B system orbits body C as a unit. The likelihood of two stars forming closely enough that their barycentre was within one of the stars, while still remaining separate bodies, is close to zero; they would simply collapse into a single star instead.

Actualy the answer is yes. That is how it is determined if 2 stars are to be considered a binary pair, or a star with an orbiting planet.

And the fact that that definition has been in use for stars is the reason given for using it with planets also.

Considering only the seperation of the stars obviously makes it unlikely to have the barycentre within one of them. However, it is common for the pair to consist of one that is orders of magnitude more massive than the other. A brown dwarf orbiting a reg giant would be one example.

There's an article or 2 over on www.space.com that explains all this.

 

[ponderingturtle]

Actualy the answer is yes. That is how it is determined if 2 stars are to be considered a binary pair, or a star with an orbiting planet.

Couldn't a definition that used enough mass to support fusion be enough of a definition of a star to seperate it from a planet? Or is there really not a good line between star and planet anymore?

And the fact that that definition has been in use for stars is the reason given for using it with planets also.

If used that way then I don't have problems with it

Considering only the seperation of the stars obviously makes it unlikely to have the barycentre within one of them. However, it is common for the pair to consist of one that is orders of magnitude more massive than the other. A brown dwarf orbiting a reg giant would be one example.

There's an article or 2 over on www.space.com that explains all this.

will look at that

 

[drkitten]

Actualy the answer is yes. That is how it is determined if 2 stars are to be considered a binary pair, or a star with an orbiting planet.

I'm sorry -- did you just say that the position of the barycentre is used to decide if a collection of two stars are to be considered two stars, or a star and a planet?

Because I would think that whether or not the second body were a star would be the relevant criterion there.

I'm reminded of the ethnic farmer who finally figured out how to tell his two horses apart -- the white one was 2cm taller than the black one.

 

[Molinaro]

Hmmm.... on re-reading I don't think I said that right. Give me a sec to go find that article. It definitely said that the same method was used for stars. Let me see exactly what they meant.

Ok, here is the line I was remembering:

In response to the criticism, Binzel said it was important to distinguish between planets and satellites. He noted that barycenters are used to define and describe double stars and so the concept should apply to planets, too.

So what exactly do they mean by that line? Is it simply saying that since they have a barycenter it means they are a double star?

This is from http://www.space.com/scienceastronomy/060816_planet_definition.html

 

[ponderingturtle]

I would have been more confortable with saying that if X is so much more massive than Y, X is a planet and Y is a moon, but if they are with in NN% of each other they are binary planets. The barycenter definition means that two objects can be in either catagory depending on their distance to each other.

And the artical did say that it was used for binary stars but did not seem to give any good indication what it was used for with binary stars.

 

[drkitten]

The barycenter definition means that two objects can be in either catagory depending on their distance to each other.

If their masses are sufficiently dissimilar. Two similarly-sized objects will never have a barycentre inside one of them unless the two objects are basically in contact with each other.

But, you know, I'm comfortable with including how close together two objects are as a factor in whether they are to be treated as one thing or two. Two objects spacially separated should be conceptually separated. Hence, a "double planet" instead of a planet/satellite.

 

[Jimbo07]

Here's a Fun link on the Pluto-Charon binary system.

 

[DRBUZZ0]

To be hones, I'm quite upset by the new tenative "planet" definition. There could verywell be dozens to hundreds of "planets" in our solar system by this definition. If you call pluto a planet instead of a sorta large planetoid...then you gotta add many others.

It's stupid. Pluto is so not Jupiter.

Here's two ideas I came up with

Idea Number 1:

A planet must be large enough to hold down an atmosphere, even if it
does not have an atmosphere (being stripped by solar winds or is in a
frozen state). It must have sufficient gravity that it could have an
atmosphere. This, of course, would raise the issue of what is an
"atmosphere." (IE: How much pressure is necessary)


Idea Number 2:

To qualify as a moon, an object must be large enough to be round.
(similar to the proposed definition of a planet). The object must
also orbit some body other than a star. If it is too small to
achieve "roundness" then it only qualifies as a minor-satellite.

To be a planet, an object must be massive enough to have a moon
orbiting it. (IE: the orbit is constantly within the bounds of the
planet or within some constraints within the planet). It does not
necessarily have to have a moon, but must be large enough to have one.



I sent them in an e-mail to Dr. Neil Tyson (because I agree with him)

but I doubt I will hear back...or that he'll even read it.

~Steve

 

[ponderingturtle]

If their masses are sufficiently dissimilar. Two similarly-sized objects will never have a barycentre inside one of them unless the two objects are basically in contact with each other.

But, you know, I'm comfortable with including how close together two objects are as a factor in whether they are to be treated as one thing or two. Two objects spacially separated should be conceptually separated. Hence, a "double planet" instead of a planet/satellite.

And I find that aestheticaly unplesant to treat the same two objects differenetly over time.

I will agree that the new definition is clear concise and can absolutely say for any known case if it is a planet or not.

Hmm, moons with excentric orbits might be intesting case, what happens if the center of mass is sometimes inside the planet and sometimes not?

 

[drkitten]

And I find that aestheticaly unplesant to treat the same two objects differenetly over time.

Really? So Ayers' Rock and the Earth should still be treated as two separate bodies, because at one point Ayers' Rock was a detached asteroid floating in space (until it crashed into the earth).

Does this mean that I could move to Ayers' Rock and claim to live in outer space?

Alternatively, since the Moon was once part of the Earth (before it was ejected), does this mean that the Moon is still part of the earth and is not a separate body?

 

[ponderingturtle]

Really? So Ayers' Rock and the Earth should still be treated as two separate bodies, because at one point Ayers' Rock was a detached asteroid floating in space (until it crashed into the earth).

Um, that is very different from any geology explanation I have ever heard of it
forming

Being sandstone from an ocean would seem to contra indicate any formation in space.

Does this mean that I could move to Ayers' Rock and claim to live in outer space?

Alternatively, since the Moon was once part of the Earth (before it was ejected), does this mean that the Moon is still part of the earth and is not a separate body?

I don't see why you need to take it to this extreem. You can easily determine two bodies that might meet the planet definition from one as that it the point of having mass in excess of structural strength, The only time that this could ever be an issue is with asteriods and ones that are basicly piles of gravel and such.

There are no conjoined twin planets or something like that, individuality is easy to determine.

 

[Wolverine]

[JAFO*]

I've put some thought into this since my previous post on the subject, and for whatever little it's worth, here are my thoughts.

This ongoing wrangling over nomenclature has irked me. Since last year’s news of the discovery of 2003 UB313, it seems to me that the majority of public discussion has centered on the least consequential aspects. What's in a name, anyway? I realize the need to have useful working definitions, but this largely resembles a strange cosmic popularity contest. The debate over the naming of names has greatly overshadowed the really important stuff -- the objects' properties, and what we can learn from them.

Personally, I have no problem with Pluto being referred to as a planet. I also wouldn’t mind if it received a demotion of any sort. Call it a Kuiper Belt Object, Dwarf Planet, trans-Neptunian Object… call it a planet with an asterisk; in the end, it doesn’t really matter. It doesn’t change Pluto’s characteristics or what ongoing study of the Plutonian system can help us understand about the distant reaches of our solar system.

I'm of the opinion that the term planet cannot be feasibly bent and stretched to accomodate scientifically significant attributes. To me, it would make more sense to design a planetary classification scheme like the Morgan-Keenan system used for stars, or the Hubble scheme for galaxies. Leave the term planet as vague as it is now (pre-IAU draft proposal), or only place very loose constraints upon it, recognizing the inherent limitations -- the word amounts to a mere placeholder suitable for use in casual discussions and little else.

But I'm neither a pro nor do I have a vote, so what do I know?

[/JAFO]

* = Blue Thunder reference.

 

[Notrump]

Committees

Q1) What does one call a horse designed by a committee?
A1) A camel

Q2) What does one call a set of planets chosen by a committee?
A2) Wanderingstarsasteroidsgasgiantssatelliteskuiperbeltobjects

Note: The software for this message board wants to put a space near the end of the long word.

 

[Notrump]

Logical Classification Helps Science

In my opinion, nineteenth century astronomers wisely demoted Ceres from initial planetary status after they discovered some of its brethren. Their small sizes, and highly eccentric and inclined orbits indicated the need for defining a new class. Those earlier astronomers felt a classification called asteroids would be more helpful in guiding the research of those seeking to understand the dynamics and origin of the solar system. For the same reason, I believe it would make more sense to place all KBO’s (including Pluto) in a class of their own.

The inclusion of Pluto’s satellite Charon in the list of 12 major planets seems especially ludicrous. Many other planetary satellites, including the Moon, are far larger. The argument seems to be that the Pluto-Charon barycenter lies above Pluto's surface. The location of a planet's surface can depend on its density. For the Moon and the other large satellites the barycenter lies within the main planet. The barycenter for the solar system oscillates above and below the surface of the Sun. Does that mean the Sun is alternately a central star and just another planet? Future students memorizing the list of planets will have a hard time understanding the difference that caused Charon to be on the list of planets and the Moon left out.

I would think that the shape of a planetary satellite's orbit relative to the Sun would be a greater consideration than barycenter. As with most non-retrograde satellites, Charon describes an epitrochoid relative to the Sun. In particular this is the type of epitrochoid that is alternately convex and concave with points of inflection (wavelike), e.g. Jupiter’s Ganymede and Callisto. Other satellites describe epitrochoids that cross over themselves (loop-the-loop), e.g. Jupiter’s Io and Europa.

The Moon is unique in that its orbit is perpetually concave toward the Sun. We think of the Earth as orbiting the Sun while being perturbed by the Moon. Normally we consider the Moon as orbiting the Earth while being perturbed by the Sun. But more so than other satellites, the Moon could also be thought of as orbiting the Sun while being perturbed by the Earth.

I would refer to the Moon as a planet before I would do so for Charon. Geophysically, I have always thought of the Moon as the first extraterrestrial planet visited by astronauts. Historically, there were seven planets (wandering stars): Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. Although in most contexts the term referred only to the latter five, as the Sun and Moon were considered to be of elevated importance to ancient naked-eye observers.

In truth, I am not calling for the Moon and other large planetary satellites to be included in the list of major planets. I’m just asking that Charon be crossed off the list. It makes those seven committee members who agreed to it look silly. They almost have me wondering if they intended to draw up a list so ridiculous that it might make others stop insisting on the inclusion of Pluto.

Let's keep all asteroids in their own class. There inability to assemble into larger bodies due to the gravitational influence of Jupiter is a story unto itself. Similarly, KBO's (including Pluto) need to be studied as members of a special class that may have been flung outward by the gas giant planets, preventing them from coalescing into larger bodies. And those bodies that are satellites of larger planetary bodies need to first be considered as part of a localized dynamical relationship.

In conclusion, I’m for a set of eight major planets. Although, I would bow to those who favor the five wandering stars (exclusive of Sun and Moon) of the ancients. My apologies to Mickey Mouse’s dog.

By the way, there is really only one Moon. The proper term for bodies orbiting planets is satellite. Yes, the generic word moon has entered the popular language. This has led some to ask why the Moon has no name of its own. It has a name in English: Moon. Of course when the Moon was first called so, there were no others to consider. Today, even some astronomers use the term imprecisely. But the enlightened ones realize the original error. The launching of artificial satellites beginning nearly 50 years ago may have caused some writers to mistakenly believe that all satellites must be artificial, leading to the greatly increased generic use of the term moon.