Pluto, Sedna and Quaoar are planetiods...

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.

"Vencislav" a écrit dans le message de
om...
http://www.gps.caltech.edu/~mbrown/sedna/

What is the definition of a planet?


It depends on the value in the market place.

When only 8 were known, discovering yet another one
is an event. The astronomer gets the credits, and it is an
event.

Then 10th is less than that, and I bet the 37645th is
much less... :-)

As the market is slumped with planet discoveries... the
worth of that designation goes down, but never to zero.

To add your name as the 37646th is maybe worth an
effort in 2104.

But we don't buy your definition.
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

"Vencislav" wrote in message
om...
http://www.gps.caltech.edu/~mbrown/sedna/

What is the definition of a planet?

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.

Who is "we?" Do you speak for the IAU, are you royalty, or do you have a
mouse in your pocket?

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.

Vencislav posted:

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.

Not really. There is no precise definition of a planet, other than it is an
object of a certain minimal size in an independent orbit around the sun. I
like the definition proposed by someone in Sky and Telescope a while back, in
that a planet is a *planetary body* which is in orbit around the sun. The
definition of a planetary body is that it is large enough so that its
gravitation would be enough to force its shape into a sphere. The Earth's
moon would be considered a planetary body (as would many of the large
planetary satellites), but would not be classed as a planet since it is in
orbit around the Earth (or the Earth-moon systems center of mass).
Using this combined definition would be more scientifically consistent and
fairly useful, although it would give us more than 9 planets in the solar
system (which is fine, as it negates the need to "declassify" something). It
would leave out most of the asteroids and the smaller Kuiper belt objects, but
would put in objects like Ceres, Quaoar, Sedna, Varuna, and a number of others
which are large enough and massive enough to form into a spherical shape.
Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

I like and agree with the terms of your definition. There are two other criteria
worth noting in the case of Pluto, as distinct from other solar orbiting objects.

The first is historical. Pluto defines the last object which qualfiied to be
considered
a planet during the age (era) of plantery discovery. Clyde Tombaugh made this
point to me several times. In addition, when Charon was confirmed Clyde commented:

'Now Pluto must be considered a planet. Any body of sufficient mass which orbits
the sun and has a body orbiting it, must be a planet.'

Perhaps others who knew Clyde better than I would have a different opinion, but my
feeling is Clyde relied on mass to define 'planets' and he thought any objects
discoverd beyond Pluto which couldbe called planets would have particular mass and
composition to qualify under that heading, as distinct from cometary bodies, and
might have at least one orbiting satellite, as a measure of their mass &
composition. I believe, but cannot prove, that Clyde thought 'planets' resulted
from a different more definate and earlier formation process, in the history of
the soalr system, vs. later Kuiper belt and Oort Cloud objects. So geology played
some role in Clyde's expectation for what a planet
was, and was not. I believe that Clyde felt any subsequent Planets-X, Y, or Z,
would
qualify according to geological requirements.

Secondly, aside from instrinsic properties, the "planet" Pluto serves as a
natural territorial marker. It defines the outer solar system as distinct from the
Kuiper Belt,
Oort Cloud, inner solar system, etc. It is entirely proper to define regional
boundaries based on shared characteristics which no bordering region possess in
the same way,
and pick some object to define that regional boundary. We do this all the time in
common daily life. It may not be scientifically pure, but it is not scientifically
"impure"
either!

When the day comes that purest-ideologues want to put up street signs on and
around Pluto fore the purpose of fire protection, then we can consider some other
scheme more in line with politics of that era, but that time has not yet arrived
.... on Pluto!

Thanks,
Jerry





David Knisely wrote:

Vencislav posted:

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.

Not really. There is no precise definition of a planet, other than it is an
object of a certain minimal size in an independent orbit around the sun. I
like the definition proposed by someone in Sky and Telescope a while back, in
that a planet is a *planetary body* which is in orbit around the sun. The
definition of a planetary body is that it is large enough so that its
gravitation would be enough to force its shape into a sphere. The Earth's
moon would be considered a planetary body (as would many of the large
planetary satellites), but would not be classed as a planet since it is in
orbit around the Earth (or the Earth-moon systems center of mass).
Using this combined definition would be more scientifically consistent and
fairly useful, although it would give us more than 9 planets in the solar
system (which is fine, as it negates the need to "declassify" something). It
would leave out most of the asteroids and the smaller Kuiper belt objects, but
would put in objects like Ceres, Quaoar, Sedna, Varuna, and a number of others
which are large enough and massive enough to form into a spherical shape.
Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Kilolani wrote:

"Vencislav" wrote in message
om...
http://www.gps.caltech.edu/~mbrown/sedna/

What is the definition of a planet?

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.

Who is "we?" Do you speak for the IAU, are you royalty, or do you have a
mouse in your pocket?

The text is quoted from the website mentioned above, so apparently this
is the definition of some people at the Caltech - especially of Prof.
Michael E. Brown.


Bye,
Bjoern

Don't forget that Charon is also a 'planet' by our current definition.
Pluto-Charon is a binary planet due to their barycenter.
....so Sedna is officially the 11th planet?

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.