To: WSFAlist at keithlynch.net
Date: Mon, 15 Mar 2004 03:03:02 -0500
Subject: [WSFA] Re: possible tenth Solar planet
From: ronkean at juno.com
Reply-To: WSFA members <WSFAlist at keithlynch.net>

On Mon, 15 Mar 2004 01:13:18 -0500 Adrienne <ase at wam.umd.edu> writes:

> It'll be interesting to see how the Pluto/Sedna planethood debate
> goes. It
> strikes me as being mostly semantics - doesn't Pluto behave as a
> Kuiper
> belt object? - but it's interesting to see why scientists hold the
> positions they do.

As far as I know, the 'behavior' of KBOs as distingushed from planets is
that KBO orbits are typically more eccentic than those of planets, and
KBOs have much larger orbits than planets.  But the most important thing
distinguishing KBOs from planets is the composition of KBOs - mixed ice
and rock and dust - and that might support Pluto being a KBO.  And Pluto
certainly has a more eccentric orbit than any (other) planet.

If categories and classifications are preumed to be merely arbitrary,
then a semantic controversy would perhaps not be of much importance.  The
crux, as I see it, is whether there is legitimately a third class of
planets (i.e. KBOs sufficently large), and that, indeed, seems to be an
arbitrary matter - how one chooses to define 'planet'.  Pluto is arguably
a KBO, but that would not necessarily mean Pluto could not also be a
planet.  If we someday find a KBO larger than Pluto, it would be bizarre
to not call the large KBO a planet, while continuing to call Pluto a
planet.  Bizarre, but not out of the question, because Pluto could be
'grandfathered' as a planet based on its historical designation as such,
or because Pluto has a much smaller orbit than other KBOs.

Most comets we observe, I think, are KBOs for which the orbit has been
perturbed, allowing them (those that become comets) to swing close enough
to the Sun to have a tail.

Ron Kean

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