12 not 9 it is then??? maybe

Andy G wrote:

" If you have any suggestions then do let us know"

I can't help thinking that they could put Jupiter, Saturn, Uranus and
Neptune in a class of their own. The rest are very minor (unless you
happen to be living on one of them, of course).

I wonder what Copernicus or Galileo wopuld have suggested.

M

Mike Williams wrote:
"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.

Doesn't the phrasing "nearly round" give some room for ambiguity?
Wouldn't it be better if there was a figure, say "90% spherical"?

Sedna and Quaoar are in this mystery zone because we don't know how
spherical or large they actually are, so what do we call them in the
meantime?


Here is the BBC's FAQ, if anyone missed it:
http://news.bbc.co.uk/1/hi/sci/tech/4798205.stm

I espcially like the last one:
"Astronomers recently discovered two new satellites around Pluto. Does
this make Pluto a quadruple planet?

No. The two newly discovered smaller bodies in orbit around Pluto are
too small and not massive enough for gravity to force them in to a
spherical shape. They are satellites, even though the centre of gravity
about which they orbit is located outside the surface of Pluto."

It's never simple is it?
Paul.

Paul Neave wrote:


No. The two newly discovered smaller bodies in orbit around Pluto are
too small and not massive enough for gravity to force them in to a
spherical shape. They are satellites, even though the centre of gravity
about which they orbit is located outside the surface of Pluto."

It's never simple is it?
Paul.

I know n body systems can be tricky to solve but it seems to me at
first glance that the barycentre of an n body system might be inside
one of the bodies or not depending on the relative positions of the
components. Does this mean the objects might alternate between being
multiple planets and satellites as they orbit each other? Can anyone
who has experience of solving this sort of problem confirm this?

Robin

In message , Cardman
writes
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 wonder how Mesklin would fit into their classification? :-)


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.

Presumably Vesta does not count because it is not spherical (why not ?).
It's certainly thought to be differentiated into core and mantle.

JRS: In article , dated
Wed, 16 Aug 2006 13:52:22 remote, seen in news:uk.sci.astronomy, Cardman
posted :
On Wed, 16 Aug 2006 12:30:35 +0100, Mike Williams
wrote:


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.


Roundness should be considered irrelevant, except as an indication.

The criterion should be one of substantial hydrodynamic equilibrium,
considering both gravity and rotation.

Otherwise the Mesklinites will get rather vexed.


From what I've seen of it, the definition does not deal with the case of
a large round thing in distant orbit around two close stars; nor that of
a satellite of a satellite of a satellite of a star; nor that of a body
which had been an undeniable planet but has lost its star.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

robin_astro wrote:
I know n body systems can be tricky to solve but it seems to me at
first glance that the barycentre of an n body system might be inside
one of the bodies or not depending on the relative positions of the
components. Does this mean the objects might alternate between being
multiple planets and satellites as they orbit each other? Can anyone
who has experience of solving this sort of problem confirm this?


Found one :-)

http://www.burtleburtle.net/bob/physics/eight.html

(Java needed)

Robin

In article . com,
robin_astro writes


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


Unfortunately the IAU website has mangled the mass criterion in the
press release web page. I await the news reports with interest. The word
document is correct.

http://www.iau2006.org/mirror/www.ia...1_release.html

"The shape of objects with mass above 5 x 1020 kg and diameter greater
than 800 km would normally be determined by self-gravity, but all
borderline cases would have to be established by observation".



--
David Entwistle

JRS: In article . com,
dated Wed, 16 Aug 2006 03:39:33 remote, seen in news:uk.sci.astronomy,
robin_astro posted :
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.

It seems unreasonable for the status of the secondary to depend on the
density of the primary; but, for fixed masses, the position of the
primary surface with respect to the barycentre is governed by the
primary density.


One might do better to classify an object according to the source of the
largest gravitational field acting on it; for a planet, that would be a
star, and for a moon that would be a planet.

Since the path of Luna is everywhere concave towards the Sun, Luna would
then be a planet.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

In message , Andy G
writes
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.
*
There's a bit here about it.

http://judge-death.livejournal.com/151080.html

Well it made me laugh.

Brian
--
Brian Howie