[meteorite-list] Pluto May Get Demoted After All

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat Aug 19 04:07:27 2006
Message-ID: <052601c6c361$fa0df2e0$7353e146_at_ATARIENGINE>

Hi, Darren,


    Unavoidable. The use of Pluto to refer allegorically to
things in the depth, in the darkness, faraway, and dead, is
centuries old. For more than a year here in the List, I've been
using the term "Plutonian" instead, but geologists speak of
"plutonian processes" and the like, so it's no better. I'm
pretty sure that there are a few cases of "one field of science
using a term with an established specific meaning in another
field of science." I just can't think of them (it's too A.M.-ish).

    It all comes from regarding the "planet" Pluto as the
prototype of a system of worlds, which it may, or may
not, be. I personally think that is a lousy idea. We don't
call the outer planets "Jupiterian" or "Jovian" worlds; we
call them "gas giants." But we do call the inner planets
"Terrestrial" worlds (after the Latin "Terra" for Earth).
But "Terrestrial" planets is now considered a bastard term
and professional scientists don't use it, I'm told...

    I've just been going through my mountain of old textbooks
going back to the 1940's (I like to collect them) up to about
the year 2000. I find the "Terrestrial" planets up through 1995.
The categories used for planets vary with the emphasis and the
bias of the writer. One has a section on "airless rocky bodies"
which puts Io, Mercury and the Moon together, then a section
on "icy rocky bodies" which puts Pluto, the Galilean satellites,
Titan, and Triton together. All the differing varieties of organization
are like creating your own categories of planetary types.

    Of course, if by a "pluton" you mean an icy rocky world,
then Ganymede is the King, not Pluto. And indeed, the IAU
says, in the draft of Resolution V: "these objects typically have
highly inclined orbits with large eccentricities and orbital periods
in excess of 200 years. We designate this category of planetary
objects, of which Pluto is the prototype, as a new class that we
call 'plutons'. "
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_resolution.html
    So, Plutons have to be inclined, eccentric, and have an orbital
period of 200 years or more... more or less. Not a compositional
class, a locational class. They're Pluto's neighbors, not Plutoclones.

    I notice that everybody in the press is calling the "plutons"
Dwarf Planets. Can't anybody read anymore? Back to the draft:
"We recognize that Ceres is a planet by the above scientific definition.
For historical reasons, one may choose to distinguish Ceres from
the classical planets by referring to it as a 'dwarf planet'." This reading
is further made clear in Footnote 3. There is apparently only ONE
Dwarf Planet, and it's cute l'il Ceres.

    EVERYBODY is calling the Plutons Dwarves. This seems a
strange reading of the text. "Dwarf" planets are in the zone of the
Classical Planets, roughly circular orbits, moderate eccentricity,
and ROUND, just not real big, according to the Draft Resolution.

    Then, there's "hydrostatic equilibrium," very strangely applied
in the language of the Draft. Footnote 3 states that "If Pallas, Vesta,
and/or Hygiea are found to be in hydrostatic equilibrium, they are
also planets, and may be referred to as 'dwarf planets'." Now, a
body is in hydrostatic equilibrium if IT DOESN'T MOVE internally
or change its shape under the forces that are continuously applied
to it. Therefore, ALL rigid bodies that do not change their shape
are in hydrostatic equilibrium, if that ALONE is the criteria. Don't
they mean in "hydrostatic equilibrium and round"? How round they
gotta be? 95% round? 90% round? 85% round? 80% round? 80%
is pretty round, but is it round enough? Jupiter is only 93.5% round;
Ceres is 93% round. Saturn is only 90.2% round. Pallas is 87%
round.

    Ceres is in hydrostatic equilibrium and is round (pretty much)
and Vesta is in hydrostatic equilibrium and not round. BUT, Vesta
(as we on this List happily know), little Vesta is a completely
differentiated planetary body, iron core, rocky mantle, crust,
the works. It must have been completely molten and plastic at
some point; how come you ain't round, little Vesta? Well, looks
like it was spinning crazily at the time and entered hydrostatic
equilibrium while still in a state of dynamic and hydrostatic
equilibrium as a tri-axial egg-thingee. (Then, it got whapped
upside the south pole with something that left a crater 80%
the diameter of Vesta which made it lose its enthusiasm for
tri-axial revolution and settle down some...)

    I guess...

    So, Vesta might get to be a (dwarf) planet, if you could
prove all that and the definition was clearer. As written, it seems
also to offer some special permission for 2003EL61, a HUGE
tri-axial egg-thingee (1960x1520x1000 km). I say HUGE because
if it were round, it would be 1500 km across, 50% bigger than
Ceres. The Footnote also mentions Hygiea and Pallas. Well,
Pallas is 87% round but Hygiea is a blob, only 70% round, not
a differentiated body. Why Hygiea? Well, it's bigger than Vesta...
And somebody, by rooting through the lists, has found a 100 km
asteroid that's really, really round; is it a planet?

    So the IAU scheme is: Eight Classical Planets, accompanied
by one Dwarf Planet, and a Orcish rabble of Plutons and Small
Bodies. Sounds like The Lord of the Rings to me.

    The Uruguayan alternative definition is stranger still. Obviously
based on the zonal theory of planet formation, it holds that a planet
is "by far the largest member of the local population of bodies."
The whole thing rests on how you define "local." Everybody
uses the planets out beyond Pluto, which they don't like anyway,
to define a "locality" and disqualify Pluto. But that volume of
space, as a zone, is far greater than the entire inner solar system.
    In fact, the inner solar system is tiny by comparison. You could put
roughly 100 inner solar systems in the zone between 38 and 48 AU!
So, if that's the size criteria, the inner solar system is a very "local"
population. So, the Earth is a planet and Mercury, Venus, Mars
and Ceres are not. Right?
    No, wait! He said, "largest by far," and the Earth is not larger
"by far" than Venus; Venus is almost as big as the Earth, so that
means that there is NO planet in the inner solar system -- it's just
a blanketty-blank asteroid belt!
    I suspect that this is what comes of cooking up theories to
fit your prejudices. Is that what the Uruguayan alternative means?
No. Is that what it says? Yes. Why is the tiny 3 AU wide patch
around the Sun so special as to have four planets in it? 'Cause
we live there, and aren't we special...? The planets may go around
the Sun, but the definition goes around the Earth.

    If you listen with your other ear to what Brown is saying
when he says 53 bodies qualify as planets under the definition,
he is saying in effect that he is finding roughly 10 planet candidates
PER YEAR, has found them. Well, he and the others that hunt,
but he seems to be the one that's bagging the game. Which may
be why he says it could go as high as 100. That just means in 10
more years, he'll find a conservative 50 more "planets." Maybe
they'll all be small round icy bodies, but maybe not. He's looking
"deeper" for "harder" objects, but the odds are good that
there's a few big ones out there...

    We can't say "minor planets" anymore; they're Small Solar
System Bodies. I suggest we all practice pronouncing "SiSSiB,"
because nobody is going to say "Small Solar System Bodies"
20 times over, very fast. Meanwhile, we can still talk about
"asteroids" which ARE NOT "little stars," which is what
"asteroid" means.

    There may be a sound method to the sparse and incomplete
Draft of Resolution V for GA XXVI. Ceres, Charon, and Xena
get to be planets right away. They demonstrate the definition by
applying it immediately to the Three Lucky Winners! One Dwarf,
One Pluton, One Double Planet, and One IAU to Rule Them All.
As for what the definitions mean, what other bodies get to be planets,
well, that will have to be decided by Committees. Committees work
slowly and deliberately. Committees try to consider everything.
Committees listen to input. Committees take their time. Probably lots
of time, during which Committee-paced time, more will become clear.
Committees will help people settle their minds, adjust, get right with
the world...

    Committees are wonderful things. And this may really be
one of those times when we need them, for just the reasons we
usually don't like them.


Sterling K. Webb
------------------------------------------------------------------------------
----- Original Message -----
From: "Darren Garrison" <cynapse_at_charter.net>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Friday, August 18, 2006 10:52 PM
Subject: Re: [meteorite-list] Pluto May Get Demoted After All


On Fri, 18 Aug 2006 20:37:34 -0700, you wrote:

>history community. These are people who know the issues, who know the
>science
>(the words and concepts are far from arbitrary),

I realized something tonight that I knew but for some reason, it hadn't
stuck me
before: the word "pluton" already has a use in science. It is a "Body of
magma
which has solidified beneath the earth". I've been on a few of them, and
can
even see one from my house when I find the right gap between the trees (this
one: http://www.shutterfreaks.com/gallery/album152/DSC_4055, photo not
mine).

So it makes me wonder-- does one field of science try to avoid reusing a
term
with an established specific meaning in another field of science (and would
some
far future geologist be looking for plutons on Plutons?)
______________________________________________
Meteorite-list mailing list
Meteorite-list_at_meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Sat 19 Aug 2006 03:34:59 AM PDT