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Lord Jubjub
2010-Jul-16, 10:48 PM
Mercury should be considered an iron planet. It's iron core is nearly half its volume.

Mars should be considered a rocky planet. It's iron core is a small fraction of its total volume.

So how should Earth and Venus be compared to these two extremes?

Hungry4info
2010-Jul-17, 08:48 AM
It's not quite as simple as "Rocky or Iron." Planets will surely have different amounts of both.

Earth and Venus are more rocky than metallic, if I'm not mistaken.

eburacum45
2010-Jul-17, 09:34 AM
Read this paper, especially the diagrams, which show a ternary relationship between three materials, Core, Mantle, and Ices.
http://arxiv.org/abs/0704.3454

Any planet we closely examine will be classifiable somewhere on these diagrams, even gas giants, which almost certainly always have a core of some sort.

antoniseb
2010-Jul-17, 12:25 PM
So how should Earth and Venus be compared to these two extremes?

Well you've invented a couple terms, and said that two planets should be labeled with these terms. The fact that only two of eight planets can be argued to fit this two-state split suggests you've left some labels out of your system.

baric
2010-Jul-17, 06:37 PM
Read this paper, especially the diagrams, which show a ternary relationship between three materials, Core, Mantle, and Ices.
http://arxiv.org/abs/0704.3454

Any planet we closely examine will be classifiable somewhere on these diagrams, even gas giants, which almost certainly always have a core of some sort.

Sweet, thanks for the link! I'm pulling this little gem out of it :P

Rp = Re × (1+0.56×IMF) × (Mp/Me)^0.262(1−0.138×IMF)

Mp = Mass of planet
Me = Mass of Earth
IMF = % of Mp that is H2O

Lord Jubjub
2010-Jul-17, 09:58 PM
Well you've invented a couple terms, and said that two planets should be labeled with these terms. The fact that only two of eight planets can be argued to fit this two-state split suggests you've left some labels out of your system.

Iron Planet (http://en.wikipedia.org/wiki/Iron_planet) is not original to me. Rocky Planet is mostly as a continuation of the ideas of iron and rocky asteroids. Mars may have an iron core, but as a percentage of volume or even a percentage of radius, it is substantially smaller in comparison to Venus and Earth, let alone Mercury.

astromark
2010-Jul-17, 10:49 PM
Ice,
gaseous and ice,
gas and solids,
rocks and gas,
rock,
and heaver mater such as iron..
and down to carbon... and what ever else you might expect...

The only certainty is uncertainty...

To make rules of composition without all the information is a folly we should avoid...

We study and observe and draw conclusions of composition by calculations of mass and orbital velocity...

There is a lot of room for error and conclusions unconfirmed... and until we put the machinery in place to test.. Unconformable...

To know the answers we ask... we need to spend the money. Guessing is unacceptable.