On Mar 21, 8:54 am, Andrew Usher wrote:
On Mar 20, 10:10 am, kT wrote:

FYI : The 'Meghar' Scale is now the defacto standard in planetary mass
classification. There is something there for everybody :

http://groups.google.com/group/sci.a...5d5976374dc39a

Well, I'm not sure how accepted this is, I find rather few hits for
'Meghar scale'.

Don't worry, it's been thoroughly discussed.

Anyway, I couldn't endorse this as a primary classification system.
The most important
characteristic of a planets is its composition, not its mass.

That's true, but composition is entirely different and much more
complex, the Meghar scale is a mass scale, and thus straightforward,
especially in an era where our knowledge of exoplanets is still
primitive, and mass and orbit are the only really clear data we have
at this point. A compositional scale is an entirely different scale,
and I encourage you to develop one, but right now the Meghar scale is
the best one out there for describing the masses and sizes of planets
with our solar system as the reference point, and it is far more
descriptive and exoplanet friendly than the crap that came out of the
IAU in the last few years. That is really a black mark on the IAU that
isn't going away.

Grouping
together a 10 Me
'super-Earth' and an equal-mass giant is hardly helpful. Certainly, a
division entirely based
on factors of 10 is unreasonable here; if we do want to use arbitrary
mass thresholds (which
we shouldn't) they should be based on physical differences: for
example, the minimum mass
(on average) to attain hydrostatic equilibrium, the minimum to retain
an atmosphere, etc.

You have to make an arbitrary decision of your breakpoints in any
scale, this scale happens to coincide remarkably with OUR solar
system. We even have an example of a planet that straddles adjacent
scales : Mercury, roughly halfway between a lunar class planet and a
Mars class planet (by mass).

Note that _any_ system will have some borderline cases; that's the
nature of classification.

i.e. - Mercury.

Groups based on mass, like the 'Meghar scale', don't really solve the
problem, they just
ignore it.

It ignores everything except mass. We further refine and distinguish
super Earths and gas planets, gas giants, super giants, solid metal
death star planets, brown dwarfs, dwarf stars, etc. In this scheme,
'dwarf' is qualitative and descriptive, just because Ceres and Pluto
are dwarfs doesn't make them non-planets, just as dwarf humans are not
non-humans. The IAU really took their eye off the 'ball' on this one.

The credit for this goes to Willie Meghar, all I did was polish it up
and present it to the scientific community, where it was immediately
embraced by most of the hard core participants in this 'debate'.

Where may I find this 'debate'? I'd like to know what others have
thought, of course.

It was on my blog : http://cosmic.lifeform.org (which is now offline).

Just because you don't see the debate, doesn't mean it didn't happen,
just as if you don't see planets, doesn't mean they don't exist.

Next up : moons of exoplanets and bizarre starlike objects.