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Date: 18 Aug 2006 11:55:29
From: Brian Tung
Subject: YADOP: Yet Another Definition of Planet (repost)
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I'm reposting this from another thread, and embellishing it a bit,
because I don't want anyone to miss what a brilliant definition this is,
which is why I've post this on Usenet. (Irony noted and ignored.)
How do planets form? Once they get large enough, by accretion. If a
body isn't sufficiently large, then an incoming piece of debris doesn't
accrete, it just bounces off. How massive does a body have to be before
an incoming piece of, say, water ice at the triple point melts to become
water at the triple point, so that it just sits there in a puzzle (and
possibly refreezes later on)? Why water? Because it's the universal
solvent.
The heat of fusion of water is about 335 kJ/kg. In order for impact to
deliver that much energy to one kg, the incoming mass must be travelling
at about 820 m/s. So an object with an escape velocity of 820 m/s
should just be able to melt an incoming piece of water ice.
Interestingly...
Pluto's escape velocity is 1220 m/s
Ceres's escape velocity is 450 m/s
Charon's escape velocity is 660 m/s
The mass of 2003 UB313 isn't currently known, but assuming it's at least
half that of Pluto, it would also have an escape velocity greater than
820 m/s.
So my proposed definition:
A planet is a non-fusor in a bound orbit with a fusor, whose
escape velocity is sufficient to melt ice at the triple point
into water.
Well, it's no crazier than what they're looking at now.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 19 Aug 2006 01:02:49
From: Chris L Peterson
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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On Fri, 18 Aug 2006 11:55:29 -0700 (PDT), brian@isi.edu (Brian Tung)
wrote:
>So my proposed definition:
>
> A planet is a non-fusor in a bound orbit with a fusor, whose
> escape velocity is sufficient to melt ice at the triple point
> into water.
There surely must be planetary bodies that have become detached from
their parent fusors, and are now wandering freely through space (a
popular device in many sci-fi stories). Does such an object cease to be
a planet? Perhaps your definition should only require that the object
originally be formed in some sort of stellar system (assuming, of
course, that such a body could form in any other environment).
Similarly, a very old stellar system may no longer contain a fusor, but
I think we'd still call any large surviving satellites "planets".
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 18 Aug 2006 19:13:35
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Chris L Peterson wrote (of my proposed definition):
> There surely must be planetary bodies that have become detached from
> their parent fusors, and are now wandering freely through space (a
> popular device in many sci-fi stories). Does such an object cease to be
> a planet? Perhaps your definition should only require that the object
> originally be formed in some sort of stellar system (assuming, of
> course, that such a body could form in any other environment).
I primarily meant my definition as an exercise, but OK, let's keep
going. I'm undecided as to whether I'd continue to call it a planet.
I might want to call it something else, especially if planets are
something that might bear life. The life-bearing possibilities are
considerably changed when the planet leaves the star! :)
> Similarly, a very old stellar system may no longer contain a fusor, but
> I think we'd still call any large surviving satellites "planets".
That's why I used the definition that says that the fusor *at any
point in its lifetime* used fusion for energy.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 19 Aug 2006 02:41:44
From: Chris L Peterson
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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On Fri, 18 Aug 2006 19:13:35 -0700 (PDT), brian@isi.edu (Brian Tung)
wrote:
>I primarily meant my definition as an exercise, but OK, let's keep
>going. I'm undecided as to whether I'd continue to call it a planet.
>I might want to call it something else, especially if planets are
>something that might bear life. The life-bearing possibilities are
>considerably changed when the planet leaves the star! :)
Come now... you don't want to break all those great old stories where
intergalactic explorers come across "rogue planets" harboring ancient
civilizations living off the dwindling heat of their planetary core. <g >
>> Similarly, a very old stellar system may no longer contain a fusor, but
>> I think we'd still call any large surviving satellites "planets".
>
>That's why I used the definition that says that the fusor *at any
>point in its lifetime* used fusion for energy.
That'll teach me to trust your SAA summary rather than reading the
entire write-up you linked.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 19 Aug 2006 14:59:19
From: Carsten A. Arnholm
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Brian Tung wrote:
> Chris L Peterson wrote (of my proposed definition):
>> There surely must be planetary bodies that have become detached from
>> their parent fusors, and are now wandering freely through space (a
>> popular device in many sci-fi stories). Does such an object cease to
>> be a planet? Perhaps your definition should only require that the
>> object originally be formed in some sort of stellar system
>> (assuming, of course, that such a body could form in any other
>> environment).
>
> I primarily meant my definition as an exercise, but OK, let's keep
> going. I'm undecided as to whether I'd continue to call it a planet.
> I might want to call it something else, especially if planets are
> something that might bear life. The life-bearing possibilities are
> considerably changed when the planet leaves the star! :)
>
>> Similarly, a very old stellar system may no longer contain a fusor,
>> but I think we'd still call any large surviving satellites "planets".
>
> That's why I used the definition that says that the fusor *at any
> point in its lifetime* used fusion for energy.
But even that isn't precise. You could argue that, according to the
definition, the Earth is a star given the efforts to use fusion for energy
production http://www.iter.org/
Splitting hairs of course, but to find a clear definition isn't easy!
--
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457
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Date: 19 Aug 2006 10:26:03
From: Davoud
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Carsten A. Arnholm wrote:
> You could argue that, according to the
> definition, the Earth is a star given the efforts to use fusion for energy
> production http://www.iter.org/
No, you couldn't. Not in a sensible way. There may be some gray areas
in the question of what is a star, but a habitable planet with an
artificial fusion reactor would lie well outside that gray area. (The
nattering nabobs of negativism haven't objected to /the/ /Earth/
falling under the proposed IAU definition have, have they?)
> Splitting hairs of course, but to find a clear definition isn't easy!
Step back a moment. Do you /really/ think that one must split hairs to
distinguish between the Earth and a star?
Y'all are starting to get silly.
Davoud
--
usenet *at* davidillig dawt com
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Date: 19 Aug 2006 16:08:54
From: Chris L Peterson
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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On Sat, 19 Aug 2006 10:26:03 -0400, Davoud <star@sky.net > wrote:
>Y'all are starting to get silly.
Surely the whole point of this thread was to be a little bit silly; that
serves the purpose of showing that the IAU, too, is being silly.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 19 Aug 2006 17:46:23
From: Carsten A. Arnholm
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Davoud wrote:
> Carsten A. Arnholm wrote:
>> You could argue that, according to the
>> definition, the Earth is a star given the efforts to use fusion for
>> energy production http://www.iter.org/
>
> No, you couldn't. Not in a sensible way. There may be some gray areas
> in the question of what is a star, but a habitable planet with an
> artificial fusion reactor would lie well outside that gray area.
Well, I was referring to ".. the definition that says that the fusor *at any
point in its lifetime* used fusion for energy".
The Earth is not a star in my subjective opinion (my reasons are tradition),
but the definition given is not clear and its interpretation is open to
other, equally valid, subjective opinions. If you think such opinions are
not "sensible", that is fine, but what's that?
> (The
> nattering nabobs of negativism haven't objected to /the/ /Earth/
> falling under the proposed IAU definition have, have they?)
I don't know. I just point to the fact that people trying to give stringent,
non-arbitrarty and objective definitions to what is a star, what is a planet
and what is a moon, have trouble coming up with formulations that most
people can accept.
>> Splitting hairs of course, but to find a clear definition isn't easy!
>
> Step back a moment. Do you /really/ think that one must split hairs to
> distinguish between the Earth and a star?
That was not my point, see above.
> Y'all are starting to get silly.
I have always been silly.
--
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457
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Date: 18 Aug 2006 19:11:54
From: Davoud
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Brian Tung wrote:
> I'm reposting this from another thread, and embellishing it a bit,
> because I don't want anyone to miss what a brilliant definition this is,
> which is why I've post this on Usenet. (Irony noted and ignored.)
>
> How do planets form? Once they get large enough, by accretion. If a
> body isn't sufficiently large, then an incoming piece of debris doesn't
> accrete, it just bounces off. How massive does a body have to be before
> an incoming piece of, say, water ice at the triple point melts to become
> water at the triple point, so that it just sits there in a puzzle (and
> possibly refreezes later on)? Why water? Because it's the universal
> solvent.
>
> The heat of fusion of water is about 335 kJ/kg. In order for impact to
> deliver that much energy to one kg, the incoming mass must be travelling
> at about 820 m/s. So an object with an escape velocity of 820 m/s
> should just be able to melt an incoming piece of water ice.
>
> Interestingly...
>
> Pluto's escape velocity is 1220 m/s
> Ceres's escape velocity is 450 m/s
> Charon's escape velocity is 660 m/s
>
> The mass of 2003 UB313 isn't currently known, but assuming it's at least
> half that of Pluto, it would also have an escape velocity greater than
> 820 m/s.
>
> So my proposed definition:
>
> A planet is a non-fusor in a bound orbit with a fusor, whose
> escape velocity is sufficient to melt ice at the triple point
> into water.
>
> Well, it's no crazier than what they're looking at now.
Yes it is. Nice try, though, if a little bit extravagant.
Davoud
--
usenet *at* davidillig dawt com
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Date: 18 Aug 2006 17:35:54
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Davoud wrote:
> > Well, it's no crazier than what they're looking at now.
>
> Yes it is.
Well, we'll have to agree to disagree on that one. In my opinion, what
they're proposing to do is just as crazy as defining how tall a hill
has to be before it's a mountain.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Aug 2006 18:58:39
From: Greg Crinklaw
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Brian Tung wrote:
> Davoud wrote:
>>> Well, it's no crazier than what they're looking at now.
>> Yes it is.
>
> Well, we'll have to agree to disagree on that one. In my opinion, what
> they're proposing to do is just as crazy as defining how tall a hill
> has to be before it's a mountain.
Bingo.
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://www.skyhound.com/sh/comets.html
To reply take out your eye
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Date: 18 Aug 2006 17:51:45
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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I (Brian Tung) wrote:
> Well, we'll have to agree to disagree on that one. In my opinion, what
> they're proposing to do is just as crazy as defining how tall a hill
> has to be before it's a mountain.
Tancredi's proposal is even crazier, from a practical perspective. It
asks us to define when a planet is "by far the largest" in its local
population. What on earth (or anywhere) does that mean?
And yet, it's intuitively what people mean when they use the word
"planet." That is probably all the more reason not to define this word
rigorously--that way madness lies.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 19 Aug 2006 08:32:38
From: Marty
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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>And yet, it's intuitively what people mean
> when they use the word "planet." That is
> probably all the more reason not to
> define this word rigorously--that way
> madness lies.
>--
>Brian Tung
I propose that the IAU do an historical search of literature and cinema
to see which bodies have been attributed with creatures living on, or in
them, or creatures which have invaded Earth. These bodies would be
classified as "planets." This may include a few stars, most notably,
Antares, and eliminates most future discoveries, but none of these
classification systems are perfect.
Marty :)
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Date: 18 Aug 2006 13:23:03
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Further expanded at
http://astro.isi.edu/notes/planet.html
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Aug 2006 13:40:03
From: Greg Crinklaw
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Brian Tung wrote:
> So my proposed definition:
>
> A planet is a non-fusor in a bound orbit with a fusor, whose
> escape velocity is sufficient to melt ice at the triple point
> into water.
>
> Well, it's no crazier than what they're looking at now.
Quite right there! ;-)
I like it, Brian.
Did you see my definition (on another thread)? I got round the whole
problem entirely! It's horribly unpopular, but as measured in terms of
how arbitrary it is, it's unbeatable. It's also historically
consistent, simple, causes little trouble for educators, and is
primarily based in science.
In case you missed it, I define a planet as any non-stellar body larger
than a dust grain that orbits a star, either directly or indirectly.
Simple eh?
I go on to define four sub groupings: rocky planets, icy planets,
gaseous planets, and traditional planets (of which there are eight or
nine, I don't much care anymore myself).
Greg
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://www.skyhound.com/sh/comets.html
To reply take out your eye
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Date: 18 Aug 2006 13:21:18
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Greg Crinklaw wrote:
> Did you see my definition (on another thread)? I got round the whole
> problem entirely! It's horribly unpopular, but as measured in terms of
> how arbitrary it is, it's unbeatable.
Do you mean that no other proposal could be more arbitrary, or less
arbitrary? :)
> It's also historically consistent, simple, causes little trouble for
> educators, and is primarily based in science.
>
> In case you missed it, I define a planet as any non-stellar body larger
> than a dust grain that orbits a star, either directly or indirectly.
>
> Simple eh?
It is simple. I'm not sure it would cause little trouble for educators,
though. :-o
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Aug 2006 14:50:15
From: Greg Crinklaw
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Brian Tung wrote:
> It is simple. I'm not sure it would cause little trouble for educators,
> though. :-o
As usual, you're more clever than I am. But ya gotta admit that I go
straight to the err... jugular of the problem. ;-)
Greg
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://www.skyhound.com/sh/comets.html
To reply take out your eye
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Date: 18 Aug 2006 14:06:32
From: Brian Tung
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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Greg Crinklaw wrote:
> As usual, you're more clever than I am. But ya gotta admit that I go
> straight to the err... jugular of the problem. ;-)
Yeowch! :)
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Aug 2006 15:57:29
From: osdfey
Subject: Re: YADOP: Yet Another Definition of Planet (repost)
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On Fri, 18 Aug 2006 13:40:03 -0600, Greg Crinklaw wrote:
> Brian Tung wrote:
>> So my proposed definition:
>>
>> A planet is a non-fusor in a bound orbit with a fusor, whose
>> escape velocity is sufficient to melt ice at the triple point
>> into water.
>>
>> Well, it's no crazier than what they're looking at now.
>
> Quite right there! ;-)
>
> I like it, Brian.
>
> Did you see my definition (on another thread)? I got round the whole
> problem entirely! It's horribly unpopular, but as measured in terms of
> how arbitrary it is, it's unbeatable. It's also historically
> consistent, simple, causes little trouble for educators, and is
> primarily based in science.
>
> In case you missed it, I define a planet as any non-stellar body larger
> than a dust grain that orbits a star, either directly or indirectly.
>
ah the old astrological definition, i guess it could work, dust grains
should be included too though
and it would probably cause even more trouble than the IAU def, but oh
well
> Simple eh?
>
> I go on to define four sub groupings: rocky planets, icy planets,
> gaseous planets, and traditional planets (of which there are eight or
> nine, I don't much care anymore myself).
>
> Greg
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