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Main
Date: 04 Sep 2006 16:09:24
From:
Subject: Why Xena Must Not Become a Planet!
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No, it's not because the ambiguities of its relationship with Gabrielle
might be a bad influence on impressionable schoolchildren.
In all the controversy over the apparent demotion of Pluto, many points
have been raised.
Isn't a dwarf planet still a planet? (Well, if so, then what about a
minor planet?)
There was a question about how an alternate resolution for defining a
planet was suddenly brought forward by a coterie of determined
dynamicists at the last minute at the IAU meeting. (Of course, one
might ask why they needed to do so; surely it is astrophysicists, and
not planetary geologists, who would outnumber them.)
And, of course, there is the history of the matter - we were used to
calling Pluto a planet for longer even than those who called Ceres a
planet (and, while they were doing so, they were calling Pallas, Juno,
and Vesta planets as well). We feel that whether or not Michael Brown
deserves the laurel wreath of a planet discoverer on his head, Clyde
Tombaugh certainly does.
But in all of this, one point seems to have been ignored.
One thing that would unite astrophysicists with dynamicists in wanting
to take extreme measures if necessary to forestall the possibility that
2003 UB 313 might _ever_ be considered for planetary status!
What was 2003 UB 313, also known as Xena, _discovered with_? Was it
some 100-inch telescope, languishing alone in some forgotten dusty
observatory, because no one had any glamorous projects to use it on?
(One _could_ say that about a 48-inch telescope, which was what got
Michael Brown started; but even though 100-inch telescopes usually are
in active use, we *do* remember that the Hooker was in a decomissioned
status for a few years.)
No. It was discovered with the Keck. Remember it? A 400-inch telescope,
atop Mauna Kea? At least in December of 1997, it was the world's
largest optical telescope! (Google and APOD are one's friends.) And I
don't recall hearing of a bigger or more important one since, although
there are a few 8-meter telescopes around which give the astronomers
who can't get time on the 10-meter Keck *something* useful to do with
their time.
No wonder there are a number of astronomers out there rather determined
not to do anything to encourage Dr. Brown to spend more of the Keck's
valuable time hunting down those - those - _vermin_ of the skies!
John Savard
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Date: 05 Sep 2006 04:41:44
From:
Subject: Re: Why Xena Must Not Become a Planet!
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tholen@antispam.ham wrote:
> John Savard writes:
> > What was 2003 UB 313, also known as Xena, _discovered with_?
> > It was discovered with the Keck.
> Incorrect.
Oh, drat. I really should have read that Discover magazine article more
carefully.
Anyways, he did use the Keck to make _some_ of his Kuiper belt
discoveries, and I believe the article at least ended with him using
time on that telescope for this purpose, so my point would still
stand...
John Savard
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Date: 05 Sep 2006 08:46:12
From: George Dishman
Subject: Re: Why Xena Must Not Become a Planet!
|
<jsavard@ecn.ab.ca > wrote in message
news:1157411364.356432.300570@m79g2000cwm.googlegroups.com...
..
> Isn't a dwarf planet still a planet?
Not as defined by Resolution 5A, that is what the whole
fight was about. The requirements of part (c) of the
definitions for "planet" and "dwarf planet" are mutually
exclusive, the first _must_ have cleared their neighbourhood
while the latter _must_not_ so a body can be either one or
the other (or neither) but not both.
> (Well, if so, then what about a
> minor planet?)
The term no longer exists in the IAU nomenclature. The
set "dwarf planets" will presumably subsume what used
to be known as "minor planets". If you still want to
use that term, I guess it would mean the six planets
other than Jupiter and Saturn though you could argue
Neptune and Uranus should be included.
> There was a question about how an alternate resolution for defining a
> planet was suddenly brought forward by a coterie of determined
> dynamicists at the last minute at the IAU meeting. (Of course, one
> might ask why they needed to do so; surely it is astrophysicists, and
> not planetary geologists, who would outnumber them.)
I guess you mean Resolution 5B. This would have added
the adjective "classical" in front of "planet in
definition (1). What that would have done was change
the grammatical structures. The set of "planets" would
have become the union of two subsets called "classical
planets" and "dwarf planets" with the word "dwarf" now
being an adjective qualifying the members of the subset
rather than part of the two word phrase "dwarf planets"
as was defined by Resolution 5A.
The result of 5B would have been to re-instate Pluto as
a planet of the subset "dwarf". The proposal had nothing
to do with astrophysics or geology but was a political
back-door attempt to keep Pluto as a planet, but I think
the voting members were smart enough to spot that and
the Resolution was rejected hence Pluto is not a planet.
> And, of course, there is the history of the matter - we were used to
> calling Pluto a planet for longer even than those who called Ceres a
> planet (and, while they were doing so, they were calling Pallas, Juno,
> and Vesta planets as well). We feel that whether or not Michael Brown
> deserves the laurel wreath of a planet discoverer on his head, Clyde
> Tombaugh certainly does.
Brown gets the credit for finding the largest "dwarf planet"
while Tombaugh now gets the credit for finding the first. It
is not clear to me how far down the list of minor planets
will be incorporated into the dwarf planets list but I guess
that's why the IAU reserved the right to identify the cutoff
for "nearly round" on a case-by-case basis.
http://cfa-www.harvard.edu/iau/lists/MPNames.html
> But in all of this, one point seems to have been ignored. ...
I'll maintain that tradition since it doesn't impinge on
the IAU resolutions.
George
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Date: 05 Sep 2006 09:00:04
From: George Dishman
Subject: Re: Why Xena Must Not Become a Planet!
|
"George Dishman" <george@briar.demon.co.uk > wrote in message
news:edj95q$qac$1@news.freedom2surf.net...
> <jsavard@ecn.ab.ca> wrote in message
> news:1157411364.356432.300570@m79g2000cwm.googlegroups.com...
>
>> ... then what about a
>> minor planet?)
>
> The term no longer exists in the IAU nomenclature. The
> set "dwarf planets" will presumably subsume what used
> to be known as "minor planets".
I should have said "dwarf planets" will presumably subsume
_some_ of what used to be known as "minor planets" while
others are now to be known as "Small Solar-System Bodies".
See part (3) of Resolution 5A and footnote 3.
http://www.iau2006.org/mirror/www.iau.org/iau0603/
George
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Date: 06 Sep 2006 13:49:36
From: Margo Schulter
Subject: Re: Why Xena Must Not Become a Planet!
|
From: Margo Schulter <mschulter@web1.calweb.com >
Subject: Re: Why Xena Must Not Become a Planet!
Newsgroups: sci.astro.amateur,sci.astro
Followup-To: sci.astro.amateur,sci.astro
References: <1157411364.356432.300570@m79g2000cwm.googlegroups.com > <edj95q$qac$1@news.freedom2surf.net>
In sci.astro George Dishman <george@briar.demon.co.uk > wrote:
>
> <jsavard@ecn.ab.ca> wrote in message
> news:1157411364.356432.300570@m79g2000cwm.googlegroups.com...
> ..
>> Isn't a dwarf planet still a planet?
>
> Not as defined by Resolution 5A, that is what the whole
> fight was about. The requirements of part (c) of the
> definitions for "planet" and "dwarf planet" are mutually
> exclusive, the first _must_ have cleared their neighbourhood
> while the latter _must_not_ so a body can be either one or
> the other (or neither) but not both.
>
>> (Well, if so, then what about a
>> minor planet?)
>
> The term no longer exists in the IAU nomenclature. The
> set "dwarf planets" will presumably subsume what used
> to be known as "minor planets". If you still want to
> use that term, I guess it would mean the six planets
> other than Jupiter and Saturn though you could argue
> Neptune and Uranus should be included.
[later clarification from George that the set "dwarf
planets" will presumably subsume _some_ of the "minor
planets," with the others as one variety of Small Solar
System Body under Resolution 5A]
Hello, and I'd suspect that "minor planets" will remain a very
useful term, as a kind of subset of "Small Solar System Bodies."
Since dwarf planets must be massive enough to have attained
near-sphericity through hydrostatic equilibrium, that leaves
thousands of minor planets, as well as comets, to populate
this third category along with "planets" (IAU sense) and "dwarf
planets." I'd suspect that the minor planet numbering system
might stay in place -- which curiously could make Ceres a
dwarf planet for some purposes, and a minor planet (not a
category in Resolution 5A) for others.
As mentioned in another post, a planetary astronomer with
dynamicist leanings, from what I could gather, remarked
to me that no special authority was needed to call a dwarf
planet a planet in the generic sense because minor planets
may be so referred to also. This it seems the term is
still current in practice.
This isn't to say that "the six planets other than Jupiter
and Saturn" isn't a witty definition in an often playful
thread!
[...]
>> And, of course, there is the history of the matter - we were used to
>> calling Pluto a planet for longer even than those who called Ceres a
>> planet (and, while they were doing so, they were calling Pallas, Juno,
>> and Vesta planets as well). We feel that whether or not Michael Brown
>> deserves the laurel wreath of a planet discoverer on his head, Clyde
>> Tombaugh certainly does.
> Brown gets the credit for finding the largest "dwarf planet"
> while Tombaugh now gets the credit for finding the first.
I'd say that while Tombaugh indeed gets credit for finding the
first and exemplary Trans-Neptunian dwarf planet (and more
generally Trans-Neptunian Object or TNO, see IAU Resolution 6A),
the credit for finding the first dwarf planet goes to Giuseppe
Piazzi for discovering Ceres on 1 January 1801.
> It
> is not clear to me how far down the list of minor planets
> will be incorporated into the dwarf planets list but I guess
> that's why the IAU reserved the right to identify the cutoff
> for "nearly round" on a case-by-case basis.
>
> http://cfa-www.harvard.edu/iau/lists/MPNames.html
What I'd suspect is that given a rough estimate for a radius
for a body (varying with composition, of course) sufficiently
massive to achieve hydrostatic equilibrium through self-gravity
might be somewhere around 800 km (Ceres is around 960 km), the
likely asteroid belt candidates might be counted on one's fingers,
maybe those of one hand. It's the KBO's qualifying that could easily
number at least 40 or 50, as I understand -- also "minor planets,"
though.
>
>> But in all of this, one point seems to have been ignored. ...
>
> I'll maintain that tradition since it doesn't impinge on
> the IAU resolutions.
By the way, one thing I'm realizing is that I do think in terms
of three subtypes of "planethood" -- major, meso or dwarf, and
minor. This is at least as much about Ceres for me as about
Pluto.
>
> George
>
>
Most appreciatively,
Margo
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Date: 05 Sep 2006 07:13:25
From: Paul Schlyter
Subject: Re: Why Xena Must Not Become a Planet!
|
In article <1157411364.356432.300570@m79g2000cwm.googlegroups.com >,
<jsavard@ecn.ab.ca > wrote:
> In all the controversy over the apparent demotion of Pluto, many points
> have been raised.
>
> Isn't a dwarf planet still a planet? (Well, if so, then what about a
> minor planet?)
.......................
> One thing that would unite astrophysicists with dynamicists in wanting
> to take extreme measures if necessary to forestall the possibility that
> 2003 UB 313 might _ever_ be considered for planetary status!
>
> What was 2003 UB 313, also known as Xena, _discovered with_? Was it
> some 100-inch telescope, languishing alone in some forgotten dusty
> observatory, because no one had any glamorous projects to use it on?
> (One _could_ say that about a 48-inch telescope, which was what got
> Michael Brown started; but even though 100-inch telescopes usually are
> in active use, we *do* remember that the Hooker was in a decomissioned
> status for a few years.)
>
> No. It was discovered with the Keck. Remember it? A 400-inch telescope,
> atop Mauna Kea? At least in December of 1997, it was the world's
> largest optical telescope! (Google and APOD are one's friends.) And I
> don't recall hearing of a bigger or more important one since, although
> there are a few 8-meter telescopes around which give the astronomers
> who can't get time on the 10-meter Keck *something* useful to do with
> their time.
>
> No wonder there are a number of astronomers out there rather determined
> not to do anything to encourage Dr. Brown to spend more of the Keck's
> valuable time hunting down those - those - _vermin_ of the skies!
>
> John Savard
"Vermin of the skies" - again? History repeats itself... :-)
http://tinyurl.com/rj6jk
http://www.crystalinks.com/asteroids.html
# Still, a century later, only a few thousand asteroids were identified,
# numbered and named. It was known that there were many more, but most
# astronomers did not bother with them, calling them "vermin of the skies".
...but at least that was the first time I've head someone referring to
transneptunian asteroids as "vermin of the skies"....
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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| |
Date: 05 Sep 2006 03:07:11
From:
Subject: Re: Why Xena Must Not Become a Planet!
|
John Savard writes:
> What was 2003 UB 313, also known as Xena, _discovered with_?
> It was discovered with the Keck.
Incorrect.
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Date: 06 Sep 2006 08:35:14
From:
Subject: Re: Why Xena Must Not Become a Planet!
|
Margo Schulter wrote:
> In sci.astro George Dishman <george@briar.demon.co.uk> wrote:
...
> > The term no longer exists in the IAU nomenclature. The
> > set "dwarf planets" will presumably subsume what used
> > to be known as "minor planets". If you still want to
> > use that term, I guess it would mean the six planets
> > other than Jupiter and Saturn though you could argue
> > Neptune and Uranus should be included.
>
> [later clarification from George that the set "dwarf
> planets" will presumably subsume _some_ of the "minor
> planets," with the others as one variety of Small Solar
> System Body under Resolution 5A]
>
> Hello, and I'd suspect that "minor planets" will remain a very
> useful term, as a kind of subset of "Small Solar System Bodies."
That should be "Minor Small Solar System Bodies" then ;-)
> Since dwarf planets must be massive enough to have attained
> near-sphericity through hydrostatic equilibrium, that leaves
> thousands of minor planets, as well as comets, to populate
> this third category along with "planets" (IAU sense) and "dwarf
> planets." I'd suspect that the minor planet numbering system
> might stay in place -- which curiously could make Ceres a
> dwarf planet for some purposes, and a minor planet (not a
> category in Resolution 5A) for others.
I'm sure the numbering scheme will remain intact, however
the "Minor Planet Center" should become the "Small Solar
System Body Center". At least the "Committee for
Small-Body Nomenclature" won't need to change.
Looking at the figure from the paper that seems to define
the criterion for 'clearing the neighbourhood' which I copied
here:
http://www.georgedishman.f2s.com/astronomy/0608359F3.png
There seems no doubt that if Pluto is a dwarf planet then so are
2003UB313, Ceres and Pallas.
> As mentioned in another post, a planetary astronomer with
> dynamicist leanings, from what I could gather, remarked
> to me that no special authority was needed to call a dwarf
> planet a planet ...
So he's another one that wants Pluto to remain a planet.
> .. in the generic sense because minor planets
> may be so referred to also. This it seems the term is
> still current in practice.
Current practice takes time to change.
> This isn't to say that "the six planets other than Jupiter
> and Saturn" isn't a witty definition in an often playful
> thread!
I'm glad you appreciate my sense of humour.
However, "many a true word ..".
> [...]
>
> >> And, of course, there is the history of the matter - we were used to
> >> calling Pluto a planet for longer even than those who called Ceres a
> >> planet (and, while they were doing so, they were calling Pallas, Juno,
> >> and Vesta planets as well). We feel that whether or not Michael Brown
> >> deserves the laurel wreath of a planet discoverer on his head, Clyde
> >> Tombaugh certainly does.
>
> > Brown gets the credit for finding the largest "dwarf planet"
> > while Tombaugh now gets the credit for finding the first.
>
> I'd say that while Tombaugh indeed gets credit for finding the
> first and exemplary Trans-Neptunian dwarf planet (and more
> generally Trans-Neptunian Object or TNO, see IAU Resolution 6A),
> the credit for finding the first dwarf planet goes to Giuseppe
> Piazzi for discovering Ceres on 1 January 1801.
Of course. I realised my error shortly after posting, thanks
for clearing that up.
> > It
> > is not clear to me how far down the list of minor planets
> > will be incorporated into the dwarf planets list but I guess
> > that's why the IAU reserved the right to identify the cutoff
> > for "nearly round" on a case-by-case basis.
> >
> > http://cfa-www.harvard.edu/iau/lists/MPNames.html
>
> What I'd suspect is that given a rough estimate for a radius
> for a body (varying with composition, of course) sufficiently
> massive to achieve hydrostatic equilibrium through self-gravity
> might be somewhere around 800 km (Ceres is around 960 km), the
> likely asteroid belt candidates might be counted on one's fingers,
> maybe those of one hand.
http://aa.usno.navy.mil/hilton/asteroid_masses.htm
I would agree with that.
> It's the KBO's qualifying that could easily
> number at least 40 or 50, as I understand -- also "minor planets,"
> though.
http://en.wikipedia.org/wiki/List_of_solar_system_objects_by_mass#Zettagram_range
If Ceres is to be one then surely 2003 EL61, Sedna and
Quaoar must also qualify
> By the way, one thing I'm realizing is that I do think in terms
> of three subtypes of "planethood" -- major, meso or dwarf, and
> minor. This is at least as much about Ceres for me as about
> Pluto.
I am happy with "planet" and "other" but if we are to
have "dwarf planet" then the application of the definition
should at least be consistent and objective. Drawing
lines on this chart works for me
http://www.georgedishman.f2s.com/astronomy/0608359F3.png
though this would be better for extension to the extra-solar
case
http://www.georgedishman.f2s.com/astronomy/0608359F1.png
best regards
George
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Date: 11 Sep 2006 01:39:30
From: Margo Schulter
Subject: Re: Why Xena Must Not Become a Planet!
|
In sci.astro george@briar.demon.co.uk wrote:
[...]
>> Hello, and I'd suspect that "minor planets" will remain a very
>> useful term, as a kind of subset of "Small Solar System Bodies."
>
> That should be "Minor Small Solar System Bodies" then ;-)
Interesting question! As I see it -- and "minor planet" is not, of
course, defined in 5A -- a minor planet is anything that is not
major, just about -- whether a spheroidal "dwarf planet" or a smaller
asteroid or KBO, etc. Thus I'd call Ceres:
1. A minor planet, because it has not "cleared its orbit"
but is a planet in a belt population.
2. A dwarf planet, because it is a minor planet which is
spheroid by reason of self-gravity.
3. An asteroid, because of its location and also, I guess,
it's likely composition (in contrast to an "ice dwarf"
like Pluto, say).
Something ranging from Vesta, say, down to the smallest catalogued
minor planets ("larger than a meteroid") would be a minor planet,
and also a Small Solar System Body or SSSB for short -- as well as
an asteroid, comet, KBO, or whatever.
Note that I'm revising my own previous usage of "minor planet" so
that it now includes both "dwarf planet" and SSSB. This fits the
traditional usage -- with the revision, of course, that Pluto would
now be both a "minor planet" and "dwarf planet" since it hasn't
cleared its orbit (minor planet) and is additionally spheroid
(dwarf planet).
I need to write this up -- and maybe show how it can be less
complicated than it might appear at first blush <grin >.
>> Since dwarf planets must be massive enough to have attained
>> near-sphericity through hydrostatic equilibrium, that leaves
>> thousands of minor planets, as well as comets, to populate
>> this third category along with "planets" (IAU sense) and "dwarf
>> planets." I'd suspect that the minor planet numbering system
>> might stay in place -- which curiously could make Ceres a
>> dwarf planet for some purposes, and a minor planet (not a
>> category in Resolution 5A) for others.
>
> I'm sure the numbering scheme will remain intact, however
> the "Minor Planet Center" should become the "Small Solar
> System Body Center". At least the "Committee for
> Small-Body Nomenclature" won't need to change.
Query: under this arrangement, would a separate "Dwarf Planet
Center" be set up? By the way, the planetary scientist on another
forum with whom I've been having an instructive dialogue takes
the view that "minor planet" (in a sense including "dwarf planets")
might come back into official vogue, and "dwarf planet" might go
out of official fashion. Personally I find them both useful -- and
ideally overlapping -- categories.
> Looking at the figure from the paper that seems to define
> the criterion for 'clearing the neighbourhood' which I copied
> here:
>
> http://www.georgedishman.f2s.com/astronomy/0608359F3.png
>
> There seems no doubt that if Pluto is a dwarf planet then so are
> 2003UB313, Ceres and Pallas.
Agreed -- noting that Ceres, smaller than the two KBO planets here
listed, has a somewhat higher "planet discriminant" or whatever we
might want to call it -- but still drastically lower than the
major planets.
>> As mentioned in another post, a planetary astronomer with
>> dynamicist leanings, from what I could gather, remarked
>> to me that no special authority was needed to call a dwarf
>> planet a planet ...
>
> So he's another one that wants Pluto to remain a planet.
Yes -- and apparently more specifically a "minor planet,"
with which I'd be comfortable also; we both take "minor planet"
(not just the larger spheroid or "dwarf planet" variety) as a
type of planet, at least as one valid usage (albeit, as he notes,
a less common one so far).
>> .. in the generic sense because minor planets
>> may be so referred to also. This it seems the term is
>> still current in practice.
>
> Current practice takes time to change.
Curious that now I'm a dedicated proponent of maintaining it --
time will tell, I guess.
Actually, for a dynamicist, I'd guess that conceptually a
"major/minor planet" dichotomy with orbit-clearing as the criterion,
and "dwarf planet" as a subcategory of "minor planet," might be
agreeable. Someone might object that calling a 1km or even 100m
asteroid a "planet" is debasing the coinage of the realm -- but
I'd take it as a well-deserved elevation of the smaller minor
planets -- or rather the making of a traditional and elevating
usage more familiar.
The point is that hierarchically, it places major/minor on a
higher taxonomic level than dwarf/SSSB.
I. Major planet -- spheroid, "has cleared the neighborhood"
II. Minor planet -- hasn't cleared the neighborhood
A. Dwarf planet, spheroid by self-gravity.
B. SSSB, insufficient mass for hydrostatic equilibrium.
Like 5A, and unlike 5B, this might give more weight to
the "clearing" criterion -- since _everything_ formally a
major or minor planet is still a planet except possibly
some asteroidal satellites of asteroids and the like, the
hydrostatic equilibrium test maybe has less "weight" than
in 5B, where it determines whether or not something is
a type of "planet."
>
>> This isn't to say that "the six planets other than Jupiter
>> and Saturn" isn't a witty definition in an often playful
>> thread!
>
> I'm glad you appreciate my sense of humour.
> However, "many a true word ..".
Indeed an apt adage!
[more on "dwarf planet" candidates]
>> It's the KBO's qualifying that could easily
>> number at least 40 or 50, as I understand -- also "minor planets,"
>> though.
>
>
> http://en.wikipedia.org/wiki/List_of_solar_system_objects_by_mass#Zettagram_range
>
> If Ceres is to be one then surely 2003 EL61, Sedna and
> Quaoar must also qualify
Yes, and I like the name Sedna, from the Inuit.
>> By the way, one thing I'm realizing is that I do think in terms
>> of three subtypes of "planethood" -- major, meso or dwarf, and
>> minor. This is at least as much about Ceres for me as about
>> Pluto.
>
> I am happy with "planet" and "other" but if we are to
> have "dwarf planet" then the application of the definition
> should at least be consistent and objective. Drawing
> lines on this chart works for me
An update: since writing the above comment, I've concluded as
mentioned above that "minor" should comprehend both "dwarf"
and "SSSB." Again, I need to do a more or less coherent writeup
on this.
> http://www.georgedishman.f2s.com/astronomy/0608359F3.png
>
> though this would be better for extension to the extra-solar
> case
>
> http://www.georgedishman.f2s.com/astronomy/0608359F1.png
Maybe you could expand a bit on the distinctions between the two
diagrams; either nicely makes the point that in our Solar System,
at least, "clearing the neighborhood" is a rather straightforward
distinction.
>
> best regards
> George
>
Most appreciatively,
Margo
|
| |
Date: 10 Sep 2006 14:15:31
From:
Subject: Re: Why Xena Must Not Become a Planet!
|
jsavard@ecn.ab.ca wrote:
> tholen@antispam.ham wrote:
> > John Savard writes:
>
> > > What was 2003 UB 313, also known as Xena, _discovered with_?
>
> > > It was discovered with the Keck.
>
> > Incorrect.
>
> Oh, drat. I really should have read that Discover magazine article more
> carefully.
I see I was quite mistaken - he kept at his otherwise unused telescope,
and just moved from plates to a CCD detector. Other astronomers, later,
used the Keck to photograph some of the bodies he found to discover
more about them.
So this isn't a war over telescope time at all.
John Savard
|
| |
Date: 11 Sep 2006 01:35:55
From: George Dishman
Subject: Re: Why Xena Must Not Become a Planet!
|
Margo Schulter wrote:
> In sci.astro george@briar.demon.co.uk wrote:
Margo, I can't reply in full at the moment but
this quick note will give you some reading in
the meantime:
> > http://www.georgedishman.f2s.com/astronomy/0608359F3.png
> >
> > http://www.georgedishman.f2s.com/astronomy/0608359F1.png
>
> Maybe you could expand a bit on the distinctions between the two
> diagrams; either nicely makes the point that in our Solar System,
> at least, "clearing the neighborhood" is a rather straightforward
> distinction.
Sorry, I thought I had cited the source, they come
from a recent paper by Soter:
http://www.arxiv.org/abs/astro-ph/0608359
The paper makes the distinction clearer than anything
I could write.
Best regards
George
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| | |
Date: 26 Sep 2006 04:56:42
From: Margo Schulter
Subject: Re: Why Xena Must Not Become a Planet!
|
In sci.astro George Dishman <george@briar.demon.co.uk > wrote:
>
> Margo Schulter wrote:
>
>> > http://www.georgedishman.f2s.com/astronomy/0608359F3.png
>> >
>> > http://www.georgedishman.f2s.com/astronomy/0608359F1.png
>>
>> Maybe you could expand a bit on the distinctions between the two
>> diagrams; either nicely makes the point that in our Solar System,
>> at least, "clearing the neighborhood" is a rather straightforward
>> distinction.
>
> Sorry, I thought I had cited the source, they come
> from a recent paper by Soter:
>
> http://www.arxiv.org/abs/astro-ph/0608359
>
> The paper makes the distinction clearer than anything
> I could write.
>
> Best regards
> George
>
Dear George,
Please pardon me for losing track of this thread for a while,
something I corrected by checking <http://groups.google.com >.
Anyway, the Soter article is indeed clear, and I should have
immediately recognized this as the source.
Anyway, what distracted me was finishing an article on planetary
definitions and typologies to which I posted a link here along with
an abstract. Also, your GAD.png is _very_ interesting, and looks quite
internally consistent. I'd love to discuss it in a new thread, maybe --
or this one, if you like.
Keeping to the bounds of this discussion, what I am inclined to say now
(with the benefit of a month to reflect) is that the IAU debate didn't
seem to focus on what I consider a very important question: "Why not retain
the older and inclusive approach that says that a 'planet' is synonymous
with 'a major or minor planet'?"
Obviously developments of the last few decades including the realization that
Pluto is part of the Kuiper Belt and that Eris is larger (whether regarded as a
KBO or a Scattered Disk Object) raise questions about the "Nine Major Planets"
model, and call for something more consistent and responsive to our new
knowledge about the Solar System.
Further, I agree with the IAU majority position that if we are trying to decide
how to classify Pluto, the fact that it is a belt object rather than a dominant
or isolated one is a relevant criterion -- indeed as also with Ceres in the
asteroid belt.
Thus it makes sense to group Ceres and Pluto together -- so far, no argument at
all on my part. However, in response to the original 16 August proposal as well
as the actually adopted 5A, I must ask: "Why should regrouping Pluto with other
belt rather than isolated planets lead to removing planetary status from a fine
asteroid like 243 Ida -- well outside the definitional criteria for 'planet' under
either set of criteria -- when it has long been considered a 'minor planet'?"
My own approach, which Daniel W.E. Green interestingly advocated in a 1996 reply to
a query about Pluto, was that certainly we should regard Pluto as a planet of some
sort -- but clearly a minor planet rather than a major planet. Thus the assigning of
Minor Planet Number 134340 to Pluto seems to me quite appropriate -- but as an
occasion to celebrate the best-known of a group of hundreds of thousands of planets
in our Solar System which deserve more attention.
Of course, advocating that "planet" (outside of official IAU contexts, where
Resolution 5A is, of course, dispositive) carry its traditionally broad and
inclusive scope doesn't mean that we can't learn from the recent controversies
and make useful categorizations.
One important dimension, of course, is the isolated/belt or major/minor distinction,
which Soter indeed presents convincingly. The issue, as I see it, is not whether
this "planetary discriminant" should be used, but how. Its best usage might be a
bit parallel to the discriminant for a quadratic equation: it tells us what kind
of planet we're considering (isolated or belt), just as the discriminant for a
quadratic equation tells us what kind of solution to expect (two distinct real
roots for a positive discriminant; a repeated real root for a zero discriminant;
and two complex roots for a negative discriminant).
Another dimension is the one focused on in the 16 August proposal, and incorporated
also into Resolution 5A: hydrostatic equilibrium, or a "graviglobe" shape (less poetic
than the "gravisphere" I found mentioned on Mike Brown's website as one description
for this test -- but more precise, or rather artfully less precise, since a "globe"
suggests an Earthlike shape with some allowance for oblation, etc.). We could classify
planets as macroplanets or microplanets based on this criterion: macroplanets are
large enough to be constrained by their self-gravity into near-spherical or "globose"
shapes, while microplanets might be found in a variety of shapes.
Anyway, this kind of philosophy might be summed up: "Include and classify."
In this kind of approach, the term "dwarf planet" seems a felicitous synonym for "minor
macroplanet" or "belt macroplanet" as long as such planets are consistently smaller (at
least in a given stellar system) than major ones, and also not too far in size from the
lower limit for hydrostatic equilibrium. A definition that might "travel better" over a
range of hypothetical systems is that a "dwarf planet" is defined as a size category for
the smallest macroplanets, with Ceres-Eris (or possibly a bit smaller, if any other
asteroids are regarded as "graviglobes") as one illustrative portion of the range. This
means, as I remark in my paper, that "dwarf planet" as a synonym for "minor macroplanet"
could be a useful "Solar System provincialism."
Again, I'd love to discuss GAD.png more -- maybe in a new thread?
Best,
Margo Schulter
mschulter@calweb.com
|
| | | |
Date: 26 Sep 2006 00:27:00
From: Thomas Lee Elifritz
Subject: Re: Why Xena Must Not Become a Planet!
|
Margo Schulter wrote:
> In sci.astro George Dishman <george@briar.demon.co.uk> wrote:
>> Margo Schulter wrote:
>>
>>>> http://www.georgedishman.f2s.com/astronomy/0608359F3.png
>>>>
>>>> http://www.georgedishman.f2s.com/astronomy/0608359F1.png
>>> Maybe you could expand a bit on the distinctions between the two
>>> diagrams; either nicely makes the point that in our Solar System,
>>> at least, "clearing the neighborhood" is a rather straightforward
>>> distinction.
>> Sorry, I thought I had cited the source, they come
>> from a recent paper by Soter:
>>
>> http://www.arxiv.org/abs/astro-ph/0608359
>>
>> The paper makes the distinction clearer than anything
>> I could write.
>>
>> Best regards
>> George
>>
>
> Dear George,
>
> Please pardon me for losing track of this thread for a while,
> something I corrected by checking <http://groups.google.com>.
> Anyway, the Soter article is indeed clear, and I should have
> immediately recognized this as the source.
>
> Anyway, what distracted me was finishing an article on planetary
> definitions and typologies to which I posted a link here along with
> an abstract. Also, your GAD.png is _very_ interesting, and looks quite
> internally consistent. I'd love to discuss it in a new thread, maybe --
> or this one, if you like.
>
> Keeping to the bounds of this discussion, what I am inclined to say now
> (with the benefit of a month to reflect) is that the IAU debate didn't
> seem to focus on what I consider a very important question: "Why not retain
> the older and inclusive approach that says that a 'planet' is synonymous
> with 'a major or minor planet'?"
>
> Obviously developments of the last few decades including the realization that
> Pluto is part of the Kuiper Belt and that Eris is larger (whether regarded as a
> KBO or a Scattered Disk Object) raise questions about the "Nine Major Planets"
> model, and call for something more consistent and responsive to our new
> knowledge about the Solar System.
>
> Further, I agree with the IAU majority position that if we are trying to decide
> how to classify Pluto, the fact that it is a belt object rather than a dominant
> or isolated one is a relevant criterion -- indeed as also with Ceres in the
> asteroid belt.
>
> Thus it makes sense to group Ceres and Pluto together -- so far, no argument at
> all on my part. However, in response to the original 16 August proposal as well
> as the actually adopted 5A, I must ask: "Why should regrouping Pluto with other
> belt rather than isolated planets lead to removing planetary status from a fine
> asteroid like 243 Ida -- well outside the definitional criteria for 'planet' under
> either set of criteria -- when it has long been considered a 'minor planet'?"
>
> My own approach, which Daniel W.E. Green interestingly advocated in a 1996 reply to
> a query about Pluto, was that certainly we should regard Pluto as a planet of some
> sort -- but clearly a minor planet rather than a major planet. Thus the assigning of
> Minor Planet Number 134340 to Pluto seems to me quite appropriate -- but as an
> occasion to celebrate the best-known of a group of hundreds of thousands of planets
> in our Solar System which deserve more attention.
>
> Of course, advocating that "planet" (outside of official IAU contexts, where
> Resolution 5A is, of course, dispositive) carry its traditionally broad and
> inclusive scope doesn't mean that we can't learn from the recent controversies
> and make useful categorizations.
>
> One important dimension, of course, is the isolated/belt or major/minor distinction,
> which Soter indeed presents convincingly. The issue, as I see it, is not whether
> this "planetary discriminant" should be used, but how. Its best usage might be a
> bit parallel to the discriminant for a quadratic equation: it tells us what kind
> of planet we're considering (isolated or belt), just as the discriminant for a
> quadratic equation tells us what kind of solution to expect (two distinct real
> roots for a positive discriminant; a repeated real root for a zero discriminant;
> and two complex roots for a negative discriminant).
>
> Another dimension is the one focused on in the 16 August proposal, and incorporated
> also into Resolution 5A: hydrostatic equilibrium, or a "graviglobe" shape (less poetic
> than the "gravisphere" I found mentioned on Mike Brown's website as one description
> for this test -- but more precise, or rather artfully less precise, since a "globe"
> suggests an Earthlike shape with some allowance for oblation, etc.). We could classify
> planets as macroplanets or microplanets based on this criterion: macroplanets are
> large enough to be constrained by their self-gravity into near-spherical or "globose"
> shapes, while microplanets might be found in a variety of shapes.
>
> Anyway, this kind of philosophy might be summed up: "Include and classify."
>
> In this kind of approach, the term "dwarf planet" seems a felicitous synonym for "minor
> macroplanet" or "belt macroplanet" as long as such planets are consistently smaller (at
> least in a given stellar system) than major ones, and also not too far in size from the
> lower limit for hydrostatic equilibrium. A definition that might "travel better" over a
> range of hypothetical systems is that a "dwarf planet" is defined as a size category for
> the smallest macroplanets, with Ceres-Eris (or possibly a bit smaller, if any other
> asteroids are regarded as "graviglobes") as one illustrative portion of the range. This
> means, as I remark in my paper, that "dwarf planet" as a synonym for "minor macroplanet"
> could be a useful "Solar System provincialism."
>
> Again, I'd love to discuss GAD.png more -- maybe in a new thread?
I always refer to the Meghar scale now for these things "
http://cosmic.lifeform.org/?p=166
That being said, among the various dwarf planets, we would also have to
differentiate between icy outer dwarfs, and rocky inner dwarfs, although
Ceres appears to be at least somewhat icy. Pluto ices are expected to be
different than asteroid planet ices too. Some outer moons are almost
completely icy. Do we have to refer then to the 'purity' of the planet?
Ceres is considerably smaller than Pluto or Charon, yet it is still
gravitationally relaxed. On the Meghar scale it is an asteroid planet.
They are all still minor planets, but it's a very easy distinction.
Even a lunar sized planet would still be considered a minor planet.
http://cosmic.lifeform.org
|
| | | | |
Date: 28 Sep 2006 08:51:14
From: Margo Schulter
Subject: Re: Why Xena Must Not Become a Planet!
|
In sci.astro Thomas Lee Elifritz <cosmic@lifeform.org > wrote:
>>> Margo Schulter wrote:
>>>
>>
>> In this kind of approach, the term "dwarf planet" seems a felicitous synonym for "minor
>> macroplanet" or "belt macroplanet" as long as such planets are consistently smaller (at
>> least in a given stellar system) than major ones, and also not too far in size from the
>> lower limit for hydrostatic equilibrium. A definition that might "travel better" over a
>> range of hypothetical systems is that a "dwarf planet" is defined as a size category for
>> the smallest macroplanets, with Ceres-Eris (or possibly a bit smaller, if any other
>> asteroids are regarded as "graviglobes") as one illustrative portion of the range. This
>> means, as I remark in my paper, that "dwarf planet" as a synonym for "minor macroplanet"
>> could be a useful "Solar System provincialism."
>>
>> Again, I'd love to discuss GAD.png more -- maybe in a new thread?
>
> I always refer to the Meghar scale now for these things "
>
> http://cosmic.lifeform.org/?p=166
This is very interesting, and raises questions about just where we might
draw lines between categories of planetary size.
> That being said, among the various dwarf planets, we would also have to
> differentiate between icy outer dwarfs, and rocky inner dwarfs, although
> Ceres appears to be at least somewhat icy. Pluto ices are expected to be
> different than asteroid planet ices too. Some outer moons are almost
> completely icy. Do we have to refer then to the 'purity' of the planet?
Certainly I agree that composition is an important distinction, and this
was one of the points of the Stern/Levison proposal suggesting a set
of categories somewhat analogous to those for stars from "subdwarf"
to "supergiant." Their system uses size as one axis, but composition as
another.
<http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf >
> Ceres is considerably smaller than Pluto or Charon, yet it is still
> gravitationally relaxed. On the Meghar scale it is an asteroid planet.
> They are all still minor planets, but it's a very easy distinction.
Yes, in my proposed system, we might call Ceres an "asteroid macroplanet."
A macroplanet in this terminology is a gravitationally relaxed one.
<http://www.bestII.com/~mschulter/inclusive_planet_def100.txt >
Here an interesting distinction is that an asteroid like 4 Vesta, although
not quite fully gravitationally relaxed, it seems, nevertheless is now often
regarded as differentiated much like a small macroplanet like Ceres -- while
some gravitationally relaxed "ice dwarfs" might not be this differentiated.
>
> Even a lunar sized planet would still be considered a minor planet.
>
> http://cosmic.lifeform.org
An interesting question here is how one defines "minor" -- which in my
approach is basically dynamical -- belt planet rather than dominant or
isolated planet (or "hegemonic planet," if one likes. However, if we
take this to be a question of intrinsic size or mass, then it's interesting
that both Stern/Levison and the Meghar Scale place a categorical line at
a bit above the mass of the Moon (roughly 1/81 Earth's mass) at about 0.03
and 0.05 respectively. For Stern/Levison this is the "subdwarf/dwarf" line,
with "subdwarf" including Ceres, Pluto, and the Moon; and "dwarf" the
terrestrial major planets (a category with an upper boundary at 10 Earth
masses).
Anyway, the question of differentiation for a very large microplanet like
4 Vesta (if one concludes that it doesn't quite represent full hydrostatic
equilibrium) is one reason I favor a flexible and inclusive approach -- but
I'd agree in any event with the addition of Ceres to the Meghar scale.
Indeed I feel strongly that Ceres should be a "household word" included in
any teaching about our Solar System, which means that the asteroid belt
and minor planets generally should get more attention, since I would
consider it very important to present Ceres at once as a gravitationally
relaxed body and as "first among equals" in a fascinating society of belt
planets, so to speak.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
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|
