12 not 9 it is then??? maybe

8 classical planets, three planets belonging to a new category called "plutons" and the largest asteroid Ceres.

The IAU draft resolution is to recognises eight "classical" planets - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - three "plutons" - Pluto, Charon and UB313 - and the asteroid Ceres. With the possibility of more to come soon.

Going to be fun when I get back to work in schools next week!! explaining all that to the kids.


--
Mr Andrew R Green B.Sc(Hons) FRAS.
StarDome Planetarium,
Web: www.stardomeplanetarium.co.uk

Andy G wrote:
*8 classical planets*, three planets belonging to a new category called
"*plutons*" and the largest asteroid *Ceres*.

The IAU draft resolution is to recognises eight "classical" planets -
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - three
"plutons" - Pluto, Charon and UB313 - and the asteroid Ceres. With the
possibility of more to come soon.

Going to be fun when I get back to work in schools next week!!
explaining all that to the kids.

What are you going to tell them about Io, Europa, Ganymede, Callisto,
Titan . . . and the Moon?

Which all seem to qualify for the new classification as 'Plutons' -
assuming that physical size is the major criterion.

JG

JG wrote:
Andy G wrote:
*8 classical planets*, three planets belonging to a new category called
"*plutons*" and the largest asteroid *Ceres*.

The IAU draft resolution is to recognises eight "classical" planets -
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - three
"plutons" - Pluto, Charon and UB313 - and the asteroid Ceres. With the
possibility of more to come soon.

Going to be fun when I get back to work in schools next week!!
explaining all that to the kids.

What are you going to tell them about Io, Europa, Ganymede, Callisto,
Titan . . . and the Moon?

Which all seem to qualify for the new classification as 'Plutons' -
assuming that physical size is the major criterion.


They have thought of this one. They are not planets. (from IAU news
release)

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary. Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

http://www.iau2006.org/mirror/www.ia...esolution.html

Robin

See the answer from Robin and the IAU definitions.

With regards the others they will still be mentioned when neccesary as being
planetary moons (we know the sizes etc), orbiting around their respective
"Classical" planets.

If you have any suggestions then do let us know

Clear Skies

Andy

--
Mr Andrew R Green B.Sc(Hons) FRAS.

"JG" wrote in message
. net...
Andy G wrote:
*8 classical planets*, three planets belonging to a new category called
"*plutons*" and the largest asteroid *Ceres*.
The IAU draft resolution is to recognises eight "classical" planets -
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - three
"plutons" - Pluto, Charon and UB313 - and the asteroid Ceres. With the
possibility of more to come soon.
Going to be fun when I get back to work in schools next week!!
explaining all that to the kids.

What are you going to tell them about Io, Europa, Ganymede, Callisto,
Titan . . . and the Moon?

Which all seem to qualify for the new classification as 'Plutons' -
assuming that physical size is the major criterion.

JG

robin_astro wrote:

They have thought of this one. They are not planets. (from IAU news
release)

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary. Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

http://www.iau2006.org/mirror/www.ia...esolution.html

Thanks for that URL Robin - I hadn't had time to search for the
definitive article after hearing a brief news report that Pluto had been
downgraded.

The IAU have possibly thrown another spanner in the works with the
specific wording used in this sub-note - referring to both Pluto and
Charon as a 'Planet' rather than a 'Pluton'. I'm sure the argument will
continue )

JG

Wasn't it Andy G who wrote:
8 classical planets, three planets belonging to a new category
called "plutons" and the largest asteroid Ceres.
*
The IAU draft resolution is to recognises eight "classical" planets
- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune
- three "plutons" - Pluto, Charon and UB313 - and the asteroid
Ceres. With the possibility of more to come soon.
*
Going to be fun when I get back to work in schools next week!!
explaining all that to the kids.

It's interesting to observe that 2003 EL61 ("Santa") isn't included in
the list of planets. So it's a "small solar system body" even though
it's considerably bigger than Planet Ceres.

Santa has over four times the mass of Ceres, but happens to be
noticeably elliptical.

"A planet is a celestial body that (a) has sufficient mass for its
self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape, and (b) is in orbit
around a star, and is neither a star nor a satellite of a planet."

So they're interpreting this to mean that the body has to actually
exhibit a "nearly round" shape, rather than just have what would
normally be considered to be sufficient mass.

That's going to make things tricky for extrasolar planets that have
masses between those of Ceres and Santa, because we're not likely to be
able to determine their actual shapes for quite a long time.


It also removes planethood from planet-sized bodies that don't orbit
stars, and doesn't provide an alternative label. Quite a few of these
things have been detected.

--
Mike Williams
Gentleman of Leisure

JG wrote:
robin_astro wrote:

They have thought of this one. They are not planets. (from IAU news
release)

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary. Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

http://www.iau2006.org/mirror/www.ia...esolution.html

Thanks for that URL Robin - I hadn't had time to search for the
definitive article after hearing a brief news report that Pluto had been
downgraded.

The IAU have possibly thrown another spanner in the works with the
specific wording used in this sub-note - referring to both Pluto and
Charon as a 'Planet' rather than a 'Pluton'. I'm sure the argument will
continue )

JG

My take on it is that "pluton" is just a subset of "planet" at the
moment, under these definitions an object can be both a pluton and a
planet. Is that how other people are reading it?

Gaz

On Wed, 16 Aug 2006 12:30:35 +0100, Mike Williams
wrote:

It's interesting to observe that 2003 EL61 ("Santa") isn't included in
the list of planets. So it's a "small solar system body" even though
it's considerably bigger than Planet Ceres.

2003 EL61 is included in the list of objects that could one day be
known as planets once they are better understood.

Santa has over four times the mass of Ceres, but happens to be
noticeably elliptical.

"Santa" is a very unusual planet-hopeful when according to popular
theory early in its history it was hit by another large KBO at a
glancing angle that resulted in "Santa" revolving at a fast rate.

In fact it currently completes a revolution each 4 hours. And since it
is more on the squishy side then the fast revolution has caused it to
stretch apart. It is in fact quite fortunate that it did not fly apart
in the process.

So it has suitable size and mass to be classed as a planet, but that
mass has been redistributed due to its unusual physics. Some
astronomers at the IAU will have a hard time figuring out if this one
should be called a planet or not.

I mean what would you decide?

"A planet is a celestial body that (a) has sufficient mass for its
self-gravity to overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape, and (b) is in orbit
around a star, and is neither a star nor a satellite of a planet."

So they're interpreting this to mean that the body has to actually
exhibit a "nearly round" shape, rather than just have what would
normally be considered to be sufficient mass.

It means that the mass must be high enough so that the object in
question suffers an internal restructuring (heavy elements sink down),
where the default outcome is a sphere shape.

This definition does not exclude 2003 EL61, when it has certainly
suffered large internal restructuring. It is just that additional
centrifugal force caused the restructuring to go in a different
direction.

That's going to make things tricky for extrasolar planets that have
masses between those of Ceres and Santa, because we're not likely to be
able to determine their actual shapes for quite a long time.

We won't be able to see them for a long time either. :-]

What astronomers need to do to figure out what extra-solar planet
hopefuls are like is to well study the samples in our own solar
system. Then they can nail down the exact figures for when hydrostatic
restructuring must have occurred. This area is currently poorly
understood, which is why the IAU are currently using the upper limit.

The first ever probe (New Horizons) is currently on its way to Pluto /
Charon and well this is a whole new area for study when there are a
quadtrillion objects out there.

It also removes planethood from planet-sized bodies that don't orbit
stars, and doesn't provide an alternative label. Quite a few of these
things have been detected.

Wondering planets is a subject that the IAU did not touch on. In my
view the IAU is trying to relabel several objects that have already
been debated and labeled by others.

TNOs, KBOs, Ice Dwarfs and now the IAU throws in... Plutons. I don't
think it will prove too popular.

I like the dwarf name myself. You cannot go wrong with that when dwarf
is another word for small, where these are without question small
planets. So Ceres can, as the IAU also agree, be a Dwarf Planet, but
your average TNO should be an Ice Dwarf Planet IMHO. Adds some
character to it after all, which will avoid boring your school
children to death.

In my view the IAU are letting themselves in for quite some hard work
and headaches. God only knows what other freaky planet hopefuls are
out there, where the IAU (with the aid of scientific debate) have to
now pick the glorious planets out from the worthless junk.

This subject should at least get a few more astronomers pointing their
telescopes towards the cold dark parts of our solar system. Just
imagine a sign out there reading "Here be planets".

I mean it is not like every day you can be the discover of a new
planet. There are likely to be a few bigger planets out there as well
just waiting to be found.

And you can rest assured that they won't have suitable funding and
equipment to be able to investigate these distant planet hopefuls to
the level that the IAU desire.

Cardman
http://www.cardman.org
http://www.cardman.com
http://www.cardman.co.uk

On 16 Aug 2006 06:50:24 -0700, "Gaz" wrote:

My take on it is that "pluton" is just a subset of "planet" at the
moment, under these definitions an object can be both a pluton and a
planet. Is that how other people are reading it?

The IAU at this time are simply trying to nail down the definition of
"planet". It seems obvious enough that sub-classification already
happens, but the IAU are just trying to define this new third dwarf
planet class.

As mentioned in my other post the exact name is bound to prove a
little sticky to pass. This would be about the fifth possible name
from what I recall. And it is far from being the best one.

Well just 8 or 9 days to go now before our solar system gets an
expected upgrade. Publishers are sure going to love reworking all
those solar system books.

Cardman
http://www.cardman.org
http://www.cardman.com
http://www.cardman.co.uk

Gaz wrote:
JG wrote:

The IAU have possibly thrown another spanner in the works with the
specific wording used in this sub-note - referring to both Pluto and
Charon as a 'Planet' rather than a 'Pluton'. I'm sure the argument will
continue )


My take on it is that "pluton" is just a subset of "planet" at the
moment, under these definitions an object can be both a pluton and a
planet. Is that how other people are reading it?

I've now had a short time to read some of the report and agree that the
IAU are suggesting two sub-classifications of 'Planet'. My initial
reaction was in response to the lazy BBC report that Pluto had been
downgraded.

JG