Maybe true, but you will need to get the IAU on board, and
unfortuately it appears that they are willing to "grandfather" Pluto
into planethood, but no other similar sized planetoids. It is there
in the popular mind, I believe, to stay, and unless I am wrong (which
I would not mind), Pluto is here to stay. Just think about this; how
long will it take for teachers at the K-12 level to accomodate the new
moons found around Jupiter, bringing the total to over 60 if memory
serves correct, at least as of last fall. For now, it remains 16, and
Saturn has more. I am simply saying that you have an uphill climb to
re-educate people when so many people do not understand basic
astronomical concepts. Maybe the IAU will be able to change the
designation of Pluto, but how long will it take to filter down to the
masses?

Erik
socalsw

(Vencislav) wrote in message . com...
http://www.gps.caltech.edu/~mbrown/sedna/

What is the definition of a planet?

It is difficult for scientists to have to define a word that everybody
thought they already knew the meaning of. But discoveries such as
Sedna, Quaoar, 2004 DW are blurring the line between planets,
asteroids, and comets. These objects are all big, so what are they? We
prefer to call them planetoids. To us, a planetoid is any round object
in the solar system that is not big enough to be considered a planet
(actually we don't know that any of these objects are round, but it is
a reasonable assumption).
So what is a planet? We define a planet to be any body in the solar
system that is more massive than the total mass of all of the other
bodies in a similar orbit. For example, many asteroids cross the orbit
of the earth. Yet the earth is more massive than all of those put
together. Thus, the earth is a planet. Ceres, the largest asteroid, is
not greater in mass than the sum of the masses of the remaining
asteroids. Hence, not a planet.

What about Pluto? Pluto sits squarely in the Kuiper belt, yet is not
more massive than the total of the other Kuiper belt objects. Thus --
like Ceres -- Pluto is no planet, just the largest object in its
class. Planetary demotion has happened before. When the first
asteroids were discovered they were called planets, since no one knew
what else to call them. As more and more discoveries piled up it was
realized that the asteroids are a separate class of bodies, the
planetary designations were revoked, and the asteroids were officially
reclassified as "minor planets." As we learn more about the solar
system our ideas have to change. The time has come for Pluto to take
its rightful place as the largest Kuiper belt object. Incidentally, if
we were self-interested we would argue the other side. Our discovery
of Quaoar is currently considered to be that of the largest known
Kuiper belt object. If Pluto were reclassified, though, Quaoar would
then be demoted to second place!

Sedna is the only object known in the inner Oort cloud, but we suspect
that there will be many more found and that Sedna will not dominate
the mass (or even be the most massive!). Thus, to us, Sedna is not a
planet.

Our definition takes our solar system from 9 planets to 8 planets.