Titan. And Titan-like exoplanets. Supertitans perhaps.

[Bad Ronald]

Titan's composition top to bottom is:

atmosphere

surface (liquid bodies, dunes, ice, mountains, etc et al)

ice crust/layer

subsurface H2O or H2O/NH3 ocean

Si core

yes?

And on Titan, CH4 (& other hydrocarbons) is analogous, even "equivalent" to H2O on Earth. H2O, or H2O & NH3, are the "equivalent" or analogue of lava & magma on Earth, making Titan's subsurface ocean like Earth's mantle. I read Titanese mountains, & other solid land, are formed by H2O, or H2O & NH3, erupting through the surface & freezing solid.

Do I have Titan's anatomy right so far?

I wonder how many Titanoid exoplanets there could be. Some may be supertitans.

Titan (& Titanoid worlds that may exist) are Earthlike yet simultaneously extremely unEarthlike.

A possible Titanoid planet or supertitan could be an Earth sized or larger planet covered in a global ocean of CH4 {&/or other hydrocarbons} possibly hundreds of miles deep with an N2/hydrocarbon atmosphere, no land or ice volcanos anywhere. Surface & air temperatures might be comparable to Titan's.

Or there could be Titanoid "Earths", possibly orbiting a red dwarf at 1 AU or so. Surface 78-80% CH4 (&/or other hydrocarbon) oceans, 20-22% land which is really frozen H2O or H2O/NH3, probably with sand dunes. Maybe a Titanoid "Earth" would have a single large moon composed primarily of frozen H2O or H2O/NH3 ice(s).

...

Your input & thoughts?

[Hungry4info]

Titan seems to lack differentiation of its interior. So it's likely that any planetary-mass bodies will not resemble Titan as far as the bulk properties go.

[EDG]

I'm quite sure that (assuming there are a lot of solid planets out there) that most of them will either have no atmosphere, or an 'exotic' atmosphere of unbreathable gases.

The trouble with "super-titans" I think is that for them to be cold and icy they'd have to be beyond the snow line of the system, and if they grow large enough out there then they'd probably end up being big enough to hold onto hydrogen and helium and snowball into jovian planets. So they'd have to be just the right size (or in the right circumstances) to somehow NOT grow into jovians, and also at the right temperature to allow hydrocarbon lakes to form on their surface. I'm not saying they're impossible, but that'd make them somewhat rare I think.