Definition of a planet

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

3) If the size of a moon is similar (to a stated percentage e.g. 80%)
to the larger body in its group it to can be called a planet if it
meets (1) and (2)
Thus it is possibe to have binary planets.

4) It would probably be necessary to specify a maximum distance from
the star in which the planet is in orbit to dis-allow wandering rocks.

Opening up a can of worms here.

My opinion.

A planet must be:

In orbit around a star.

Must be the sie of Pluto or larger.

have enough mass to pull itself into a spherical shape.

not a part of an asteriod belt

This would excude Ceres, which is spherical in shape.

Matthew Ota

steve wrote:
With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

3) If the size of a moon is similar (to a stated percentage e.g. 80%)
to the larger body in its group it to can be called a planet if it
meets (1) and (2)
Thus it is possibe to have binary planets.

4) It would probably be necessary to specify a maximum distance from
the star in which the planet is in orbit to dis-allow wandering rocks.

Stephen Colbourne writes:

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

The problem with any definition that relies on size is that we don't
know the sizes of newly discovered objects in the outer Solar System.
Heck, the size of Pluto wasn't even known until the late 1980s.

wrote:

Stephen Colbourne writes:

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

The problem with any definition that relies on size is that we don't
know the sizes of newly discovered objects in the outer Solar System.
Heck, the size of Pluto wasn't even known until the late 1980s.

In any case the definition has been altered a number of times since it
meant a visible "wandering" star.


Eugene L Griessel

It's morally wrong to allow naive end users to keep their money.

Two Types- of -planets,and they are rock and gas. Left over gas that
formed the stars gave us gas planets.(failed stars) Heavy dense stars
that created heavy elements and then exploded (supernova) gave us rock
planets,and carbon for life. Bert

steve wrote:
With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

3) If the size of a moon is similar (to a stated percentage e.g. 80%)
to the larger body in its group it to can be called a planet if it
meets (1) and (2)
Thus it is possibe to have binary planets.

4) It would probably be necessary to specify a maximum distance from
the star in which the planet is in orbit to dis-allow wandering rocks.

Planets orbit stars individually. Moons orbit planets individually.
Planets must be planet size, moons must be moon size. Rocks are odd
shaped. Dust is dust.

--
Two ways to improve your life.
1. Turn off the TV.
2. Throw it out the window.

Vlad the Impaler

On 13 Jun 2006 00:29:10 -0700, "steve"
wrote:

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added...

It is silly to even attempt a technical definition. Since planet already
has non-technical meanings, this will only lead to confusion. The
smartest thing would be to simply create some new definitions (or
modifiers) for the types of bodies we are familiar with. Leave "planet"
to popular usage.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On 13 Jun 2006 00:29:10 -0700, "steve"
wrote:

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added...

It is silly to even attempt a technical definition. Since planet already
has non-technical meanings, this will only lead to confusion. The
smartest thing would be to simply create some new definitions (or
modifiers) for the types of bodies we are familiar with. Leave "planet"
to popular usage.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com





--
Gareth Slee

Chris L Peterson wrote:

On 13 Jun 2006 00:29:10 -0700, "steve"
wrote:

With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added...

It is silly to even attempt a technical definition. Since planet already
has non-technical meanings, this will only lead to confusion. The
smartest thing would be to simply create some new definitions (or
modifiers) for the types of bodies we are familiar with. Leave "planet"
to popular usage.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

How about?
Greater than 1000Km - Major Body
Between 20 and 1000Km - Medium Body
Less than 20 Km - Minor Body

Although you'd probably need more ranges.

--
Gareth Slee

steve wrote:
With this set to be finalised fairly soon in September 2006 I think it
is essential that a few sensible parameters are added.

1) A body in orbit around a star.

2) Size must be larger than Pluto ( or another agreed specified size
and mass) to give a minimum size UNLESS extra-terrestial life is found
on the planet when a much smaller size would be allowed.

3) If the size of a moon is similar (to a stated percentage e.g. 80%)
to the larger body in its group it to can be called a planet if it
meets (1) and (2)
Thus it is possibe to have binary planets.

4) It would probably be necessary to specify a maximum distance from
the star in which the planet is in orbit to dis-allow wandering rocks.

To me it's easy: There are eight planets, Mercury through Neptune.
They are all in circular orbits. They don't cross any other planet's
orbit. They're not part of a group of objects. With the exception of
Mercury, they are larger than any other known objects in the solar
system.

The remainder are asteroids, KBO's, comets, and satelites. The only
remaining object not known to be part of a group is Sedna, and it
probably is part of a yet unknown group.

Consider this: Neptune's moon Triton is believed to be a captured KBO,
and is larger than Pluto. Prior to its capture by Neptune, was Triton
a planet?