Re: "Pluto Now Called a Plutoid"


"David M. Palmer" <dmpalmer@xxxxxxxxx> wrote in message
news:200720082158484697%dmpalmer@xxxxxxxxxxxx
In article <bRmzWNFB32gIFwZt@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Dr J
R Stockton <jrs@xxxxxxxxxxxxxxxxxx> wrote:

In rec.arts.sf.science message <gKydnf5iLJilDhzVnZ2dnUVZ_sPinZ2d@comcast
.com>, Sat, 19 Jul 2008 00:09:36, K_h <KHolmes@xxxxxxxxx> posted:

Look again at the phrase used "(nearly round) shape". It is clearly
restricting the object to be nearly spherical in shape (from webster's
definition of round).

The "nearly round" criterion should be taken to require an axis of
rotational symmetry, not an infinite number of such axes. Remember,
Mesklin is and should be a planet.

Actually, a planet spinning fast enough will be triaxial. Spin it
more, and it goes pear-shaped.
http://www.josleys.com/show_gallery.php?galid=313

But anyway, by the IAU definition, Mesklin is not a planet, because it
does not orbit the Sun.

The IAU seems to be be stuck in the heliocentric era: they also defined
the North pole of all astronomical objects, throughout the Universe, by
reference to the solar system's invariable plane, instead of the
correct definition of being the counterclockwise pole.

--
David M. Palmer dmpalmer@xxxxxxxxx (formerly @clark.net, @ematic.com)

Thank you very much for this information; I was unaware of this work. In
light of this, I believe a good definition of planet should avoid any
mention of "round", "spherical" and "spheroidal" and simply use the phrase
"hydrostatic equilibrium". So my own example definition is flawed in this
regard and it should be altered to remove the phrase "is nearly spherical or
nearly spheroidal in shape". So the corrected example definitions are
listed below for anyone who is still interested in them. The IAU will
someday break out of its heliocentric rut.


Thanks again for the pointer.

k

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A star is a celestial body that sustains, has sustained, or is capable of
sustaining nuclear fusion.

A brown dwarf is a star that is only capable of fusing deuterium and/or
lithium even if neither is present.

A celestial body that has its barycenter continuously inside the body of
another celestial body is a satellite of that celestial body.

A planetary body is a celestial body that is not a star and has sufficient
mass for its self gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium.

A planet is a planetary body that is not the satellite of another planetary
body.

A moon is a satellite of a planet.
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Relevant Pages

  • Planet Definition
    ... A planet is a celestial body that is by far the largest object in ... energy by any nuclear fusion mechanism. ... I like Pluto because when I ... was young it was the most distant planet from the sun and now Neptune ...
    (sci.space.policy)
  • Definition of a Planet
    ... A planet is a celestial body that is by far the largest object in ... energy by any nuclear fusion mechanism. ... I like Pluto because when I ... was young it was the most distant planet from the sun and now Neptune ...
    (sci.astro)
  • Re: Planet Definition
    ... :A planet is a celestial body that is by far the largest object in ... :lie close to the plane of the elliptic. ... :was young it was the most distant planet from the sun and now Neptune ... So if evidence came forward that, say, Earth was a 'wanderer' it would ...
    (sci.space.policy)
  • Re: "Pluto Now Called a Plutoid"
    ... clear if it qualifies as a planet. ... consider a solar system with a 6 solar-mass star orbited by a 25 ... That is an actual potential ambiguity, at the moment we don't know of any such bodies if we find one then we will have to decide. ... A star is a celestial body that sustains, has sustained, or is capable of ...
    (rec.arts.sf.science)
  • Re: "Pluto Now Called a Plutoid"
    ... hydrostatic equilibrium and is nearly round. ... general, parentheticals are for clarification only, and the greater ... about "hydrostatic equilibrium", and not a further restriction of it. ... The people who wrote the definition consider Saturn to be a planet. ...
    (rec.arts.sf.science)