This is just an idea that might be nice to implement. So I'll try to write about it, maybe you will like it. Recently, I have been reading about exotic class of the so-called carbon planets. The idea is, that the composition of the protoplanetary discs varies from region to region of space. As one of the proponents of the carbon planet hypothesis writes, it is known that is there is significantly more carbon compared to the oxygen (C/O metallicity ratio > 0.98), silicone oxides that constitute the mantle of many terrestial planets would not form and they would be replaced by carbides (SiC, TiC). The crust of the planets would be composed of mostly graphite or diamond and there could be oceans of tar. (Probably many more things, but I am not very strong in chemistry.) Such planets would probably have some interesting features:
* there would probably be no water, the oxygen in it would reduce to CO * there would not be rocks (oxides of Si, Mg, Ca), instead, there could be some carbide rocks. (only different color? maybe slightly different shapes?) * there would be either almost all the planets out of sillicates, or out of carbides in the star system, as it depends of the C/O ratio of the original nebula * atmospheres would look differently, probably Titan-like?
Some nice sample systems and also the assumed frequency ~30% of the carbon-rich systems can be found in Fig.1 and Figs. 4,5 here. What do you think? Any interesting comments about how could these planets look like?
I have been searching the forum - I did find that the carbon planets are mentioned time to time in various threads, but I didn't find thread where one could discuss various aspects of this issue (areas of their probable location, probability of occurrence, features on the surface or in the atmospheres). Maybe such discussion would be interesting? But I'm sorry if this thread is redundant, next time I will search more carefully.