Carbon Worlds

Adamean Type Worlds

Adamean Planet
Image from LordOther
Carbon-rich Terrestrial worlds
Most planets form from protoplanetary clouds where the ratio of carbon to oxygen is less than one, and oxygen predominates in the formation process. If the accretion disk has a carbon/oxygen ratio greater than one, carbides and graphites condense out far more readily than do silicates, which make up the bulk of more common terrestrial worlds.

The resulting worlds also lack water, since H2O reacts with metal carbides. Any water-ice impactors that arrive will react with the carbides already present and produce hydroxides and methane. Steam from the impactor also reacts with graphite in the crust to release hydrogen and carbon monoxide.

A large carbon world generally has a lower crust or upper mantle of compressed diamond, which conducts heat readily and allows the core of the planet to cool more rapidly than a silicon-rich world with an equivalent mass. The cool core can only produce a weak magnetic field, an effect which leads to increased atmospheric loss.
Carbon planet
Image from Steve Bowers
Adamean worlds - cross-section

These worlds have atmospheres largely composed of carbon monoxide, methane, and long-chain carbon compounds synthesized photochemically in their atmospheres. Indeed, this last substance often precipitates and evaporates on a carbon planet's surface, and seas and lakes of oil or tar-like substances often form.

Image from Steve Bowers
Solaris, a carbon world (Adamean type) has oceans of hydrocarbons and an atmosphere rich in organic compounds; there is, however, no life on this world. The planet is currently surrounded by a low-gravity Ribbonworld structure, mostly constucted from carbon nanomaterials.

Carbon worlds are typically less dense than Ferrinian worlds, and slightly less dense than Eugaian worlds, but denser than most waterworlds.

Alternative biochemistries sometimes emerge on adamean worlds, using hydrocarbons instead of water as solvent. These rarely develop beyond the prebiotic stage. One exception is the complex biosphere which has evolved on the world Uwa Mmanu, a large carbon world with multicellular heterotrophs and autotrophs.

Ndiangu Mme Anwu
Image from Steve Bowers
The carbon world Uwa Mmanu, a superterrestrial adamaean type planet

Image from Steve Bowers
Labrayuh, a carbon world orbiting 61 Cygni B

Image from Steve Bowers
Konsheir - a temperate carbon world orbiting Glim.

Image from Steve Bowers
A image of the surface of the Petrolic world Globe, simulated with the cloud cover removed
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Development Notes
Text by John M. Dollan and Steve Bowers
Acknowledgements to Martyn Fogg for his assistance and suggestions
Initially published on 18 November 2008.

Additional Information

A Powerpoint presentation by Martyn Fogg on the subject of Carbon planets is available here