Just noticed something...

[Omnigeek6]

Kepler-11f: 2.3 earth masses, but with the density of Saturn.

Is this just a terrestrial with a huge atmosphere, or do we get to call it a "puffy earth"?

[atomic7732]

puffy earths  

Well with a radius of .66 Neptunes... I'm gonna say this is a really low mass gas planet... A puffy earth/dwarf giant...

Well, if it was the atmosphere...Then uhh... that's really thick to be able to detect...

[Omnigeek6]

I propose a new system of planet classification based on composition and size. 0-10 earth masses is a "dwarf", 10+ is a giant.

We would have:

Rock Dwarfs (All our system's terrestrial planets, and some super-earths).
Rock Giants (Any rocky planet above 10 earth masses. Might include some cthonian planets).
Ice Dwarfs (Pluto and other KBOS. All the ice dwarfs in our system are dwarf planets, but larger ones could exist)
Ice Giants (Uranus and Neptune, as well as probably some other planets of similar mass).
Wet Dwarfs (An ice dwarf that gets in too close; consists mostly of liquid volatiles. Could include many super-earths.)
Wet Giants (might include a few neptune-mass planets inside the frost line)
Gas Giants (duh).

And now, the first Gas Dwarf planet!



what do you guys think?

[atomic7732]

I googled something the other day and I thought I saw something saying that a dwarf is < 10 earth masses. Huh. Did you find that somewhere?

I like the classification... but I don't think there will be many rock giants. You may also need to make a more firm dividing line... Give some densities.   2.64 g/cm^3 is silica... So maybe 3 g/cm^3 and higher would make something a "Rock"y planet, rich in iron, silica, and other metals like nickel and cobalt.

[Omnigeek6]

I googled something the other day and I thought I saw something saying that a dwarf is < 10 earth masses. Huh. Did you find that somewhere?

I like the classification... but I don't think there will be many rock giants. You may also need to make a more firm dividing line... Give some densities.   2.64 g/cm^3 is silica... So maybe 3 g/cm^3 and higher would make something a "Rock"y planet, rich in iron, silica, and other metals like nickel and cobalt.

Ah. I've found something.

Gas Giant page on Wikipedia:

Planets above 10 Earth masses are termed giant planets.[1] Below 10 Earth masses they are called super earths or, sometimes probably more accurately for the higher mass examples, "Gas Dwarfs" e.g. as suggested by MIT Professor Sara Seager[citation needed] for Gliese 581c using a model where that exoplanet was mostly composed of hydrogen and helium. The term "gas dwarf" was also used previously by others.[2][3]

With this terminology in mind, some astronomers are starting to refer to Uranus and Neptune as "ice giants" to indicate the apparent predominance of the "ices" (in liquid form) in their interior composition.[12]

So, if we define "gas" as hydrogen and helium, "ice" as volatiles, and "rock" as metals and either silicates or carbon compounds (http://en.wikipedia.org/wiki/Carbon_planet), than we have a partial classification.

We can also define transitional states, such as Pluto (transition between ice dwarf and rock dwarf), and hypothetical planets which contain roughly equal proportions of rock and gas, ice and gas, or all three.

Further subclasses could also be defined.

For example, ice dwarfs could include a "wet" subclass, consisting of planets with a well-defined liquid surface (as opposed to a gaseous atmosphere transitioning to supercritical fluid, as is found on most giant planets), and a "steam" subclass, referring to planets hot enough to have their volatiles in gas and supercritical fluid states.
Rock planets would have "oxygen" and "carbon" subclasses, as well as a "lava" subclass for each of those (reserved for planets extremely close to their stars, or moons undergoing absurd amounts of tidal heating.
Gas planets (and possibly ice giants) would use the Sudarsky classes.

[atomic7732]

I wonder if there is somewhere, or someone who has calculated the physical highest possible rocky planet mass... Could you really have a rock giant?

Also 55 Cancri e transit observations show that it is 2 times as dense as earth... and exact opposite of this puffy earth you have of Kepler-11 f

[Omnigeek6]

I wonder if there is somewhere, or someone who has calculated the physical highest possible rocky planet mass... Could you really have a rock giant?

Also 55 Cancri e transit observations show that it is 2 times as dense as earth... and exact opposite of this puffy earth you have of Kepler-11 f

Well, since 55 Cancri is a very metal-rich star, it would be a good place for a high-density planet to form.

I'm suspecting an iron planet: http://en.wikipedia.org/wiki/Iron_planet

As for rock giants: as far as I know, a rocky planet of sufficient mass would draw in gas and volatiles, and end up as a gas or ice giant. However, it could of course only do so if lots of gas and volatiles were available. If my understanding of planet formation is correct, inside the frost line, such substances are difficult to come by. Therefore, the theoretical maximum mass for a terrestrial planet should be the total amount of mass inside the frost line. In our own solar system, the total mass of surviving material within the frost line is slightly less than 2 earth masses, with the largest single object taking up about half of that mass. However, as you have noted, planets of higher density than earth have been found with several times the mass, implying rocky compositions. If several such planets were able to form, and collided, a rock giant could be formed.

In addition, the cores of some large gas giants could, if they became cthonian planets, still exceed 10 earth masses, and so qualify for this definition.

Note: rock giants would probably be comparable in mass to ice giant, not to gas giants.