Carbon planets

[Brendan]

If there is lots of carbon or too little oxygen for silicates to form, inner planets could be carbon planets. Lower mass extrasolar planets like the ones at PSR 1257+12 could be of that type.

http://www.universetoday.com/am/publish/diamond_worlds.html?1022005

What would they look like? What kind of planetery processes would they have? Could they have plates and oceans?

[TERRIER]

Don't know about plates and water oceans, here's a quote from another article;

http://msnbc.msn.com/id/6934625/

Carbon planets might have smoggy atmospheres laden with carbon dioxide, and a surface covered with tarlike precipitation. "A little bit like Los Angeles," Kuchner said.

Future telescopes might identify some of these offbeat orbs by noting these characteristics and a lack of water.

[ajtribick]

Hmm... if these worlds are poor in water, perhaps they might be suitable locations for more "exotic" biologies, e.g. ammonia-based, where water would be dangerously acidic.

[eburacum45]

Okay; what about a carbon rich, water rich world; why is that so unlikely?
Water is a very common compound, and would be plentiful in a carbon rich planetary system too.

Let's see; carbon dioxide would form, as well as water; this would lead to the formation of carbonic acid; carbonic acid would cause chemical erosion-
carbon dioxide would be continually given off and redissolved by this reaction.
I think that moist carbon worlds would be subject to fierce greenhouse effects, heating the atmosphere and driving water vapour to the top of the atmosphere where it could be split by photodissociation.

However there should be a class of cool moist carbon worlds, perhaps orbiting K class orange dwarfs, where the greenhouse effects of water and CO2 are just enough to keep the water liquid, but not enough to boil it away; these planets might have carbonic acid seas, just like the seas astronomers once thought existed on Venus. (before they found it was dry.)
I described the terraformation of a carbon rich planet here-
http://www.orionsarm.com/worlds/Ribblehead.html
but the new ideas about carbon rich worlds are even more extreme. It might not be possible to terraform such an oily, dry, chemically eroded world after all.