Re: "Pluto Now Called a Plutoid"

On Jun 12, 8:15 am, Bryan Derksen <bryan.derk...@xxxxxxx> wrote:

There's already a class of object called "Plutinos", which overlaps
significantly (though apparently not completely) with these Plutoids.
That's likely to be confusing.

Since Plutinos are *only* those bodies which share the same 2:3
resonance with Neptune that Pluto has, but regardless of size, while
there will be confusion due to the similarity in the names, they still
refer to very different (although overlapping) classes of objects.

We do already have terms for "gas giants" and "terrestrial planets";
some have noted that the whole idea of a 'planet' is flawed, because
the gap between those two is much greater than the gap between the
terrestrial planets and either the Kuiper Belt bodies or even the
asteroids.

A tiny chunk of rock in space is a meteoroid; when it plunges through
the Earth's atmosphere to be a light in our sky, it's a meteor, and
when it hits the ground, it's a meteorite.

By analogy, perhaps a comet should be called a cometoid when it's too
far from the Sun to have a tail - or, at least, an icy body, similar
to a comet, but the orbit of which never goes near enoough to the Sun
to allow a tail to be manifest, should be called a cometoid. This term
would apply, for example, to Chiron and the other Centaurs.

Starting from that, Pluto and the other large Kuiper Belt objects
would become quasi-planetary cometoids, or QPCs. However, this
wouldn't quite be synonymous with Plutoid, since the size threshold
would be lower, perhaps at 1.5 times the radius of Ceres.

If the Kuiper Belt is found to have bodies in it with a diameter equal
to or greater than that of Mercury, but which are not desired to be
called planets because they're in the same belt with other objects of
varying size, those objects could simply be called PCs; planetary
cometoids.

As for Pluto, however, since it _is_ much larger than any other
Plutino, it _has_ cleared its own orbit of everything but debris, even
if there are similar bodies in orbits only a little further out, so it
could be left as a planet (but then its diameter, rather than
Mercury's, would mark the dividing line between a QPC and a PC). That
would also mean that Eris would become a planet after we knew that it
was significantly bigger than all the Erisinos out there...

John Savard
.

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