[meteorite-list] Repost: PLANETS, PART TWO

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Wed Aug 3 04:38:10 2005
Message-ID: <42F0824A.C753A39F_at_bhil.com>

Hi, Everybody!

    My original message must have been too long. It didn't post. Here it
is in parts.

    Part Two:

    My definition of a planet in my original post (WHAT IS A PLANET?)
was as follows: if it goes around the Sun and is demonstrably larger
than Ceres, IT'S A PLANET.

    As for sphericity, anything as big as Ceres is going to be
spherical, so that roundness is implied, since at this size no material
could withstand the crushing forces of gravity, neither the lightest
ices nor iron itself.

    Then, there would then be three classes of planets: the Terrestrial,
the Jovian, and the Plutonian planets. Naming by example is always a
good choice before you know everything. (The word is "Plutonian," AL. I
didn't coin it; it already existed.)

    Three kinds of planets, all bigger than Ceres; two kinds of minor
planets: the Terrestrial, from Ceres down to a small NWA precursor, and
the Plutonian ones; hellride comets; and trash like zodiaical dust...
There's your solar system.

    This preserves the terrestrial minor planet class, or asteroids, as
it is and as it should be understood, instead of forcing us to throw
Pluto and all the 100's of KBO's already known into the existing minor
planet class and have them messily displace Ceres and Vesta and...

    Stern's definition, by the way, would make the spherical minor
planets (Ceres, Vesta, etc.) full planets, just like you want, Doug.
It's OK by me, if you can talk'em into it!

    As for the criteria of sheer size, what about the common complaint
that Pluto and 2003UB313 and the KBO's just aren't "big enough" to be
planets? Well, compared to Jupiter, the EARTH isn't big enough to be
considered a planet, either! Just rubble, mere space junk...

    These are three distinct and easily definable compositional classes,
with their own distinct formational histories. They are: bodies of rock
(including iron) and few volatiles, the terrestrials; bodies of
volatiles (and perhaps a little rock), the Jovians; and bodies of both
rock and volatiles, the Plutonians.

    Anything larger than a MINOR planet is a MAJOR planet, or A Just
Plain Planet. Simple, isn't it?

    Notice the logical completeness of this three-fold definition. It
is, when stripped bare, essentially this:
    1) ALL rock,
    2) ALL volatiles, and
    3) significant admixtures of rock AND volatiles (half and half or
whatever it happens to be).

    These are all of the logical combinations of these two principal
ingredients of a solar system, since this how we usually divide the
elements: by their thermal behavior and their most common physical state
in the universe at large.

    Pretty fundamental, really.

    A few obvious things jump out.

    The Terrestrial planets are made from volatile-free rocky-iron
planetesimals, the non-accreted survivors of which are the asteroids, or
Minor Planets. Many of the minor league players are not really so minor;
if Ceres had a stable orbit between Venus and Mercury, we'd call it a
planet, no problem, and would have been calling it so for thousands of
years, as it would be a naked-eye planet there.

    The Jovian planets are largely made from volatiles, not
planetesimals, so there are no survivor planetesimals. But there were
some rocky planetesimals (In the same region? Further out? Further in?
Good question...) that held on to some of those same volatiles
themselves, despite likely competition from the Jovian planets. (That's
some competition!) They are the Plutonian major and minor planets.

    There are hundreds of them (already). There could be thousands. Some
are more rocky (like Pluto); some are less rocky (like Charon, its
moon). There are Plutonian Minor Planets (smaller than Ceres), probably
a huge number, just like our numerous Terrestrial Minor Planets, the
asteroids.

    It's a New Solar System.

    Those that are bigger than Ceres are Planets (Period), just like
Mercury is a planet and not an asteroid, despite the fact that it is not
even half again as big as the Earth's Moon, which would be a planet if
it weren't in orbit around US and went around the Sun instead. (Being a
satellite is just luck of the draw, you know.)

    Not to be a trouble-maker (who? me?), but there's a chance that
Mercury is SMALLER than 2003UB313... Whoops! So, will that make Mercury
an asteroid? Hey! If 2003UB313 is, then... What about the NEXT and
bigger one to be discovered? It will be, you know.

    You may have already noticed a pattern of zoning here. There are the
Terrestrials with some minor planets among them (Apollos, Amors, Atens).
Outward of the Terrestrial major planets are the Terrestrial minor
planets.

    Outward of them are the Jovian planets, with satellites many of
which are captured "inner" Plutonian planets.

    The Plutonian planets are unlikely to be merely escaped or ejected
Jovian planetesimals (analogous to the terrestrial minor planets),
because if the Plutonians were, the Jovians would be far rockier (and
denser) than they are. (Saturn would float if you had a bathtub big
enough.) Not that it would be significant if the Plutonians were; the
Earth would be a planetesimal to something the size of Jupiter!

    Outward of the Jovian planets are the Plutonian planets themselves,
major and minor. We have not discovered enough of them to know if there
is any concentration or zoning of the orbits of minor and major
Plutonian planets. But we will, in time.

    The big ones? I say they're planets, pretty much regardless of what
some pissant in Paris says next week. If I had the IAU's email address,
I'd copy this to'em.

    If the Plutonian planets can survive competition from Jovian
planets, they can withstand the IAU, I do believe.


Sterling K. Webb
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Received on Wed 03 Aug 2005 04:37:30 AM PDT