Could a carbon planet have been formed in the solar system?

[Shraa]

Specifically, could Venus have otherwise formed as one, while leaving the rest of the structure of the solar system pretty much intact?

Failing that, could one have formed anywhere in the solar system?

 

[Vagn]

Specifically, could Venus have otherwise formed as one, while leaving the rest of the structure of the solar system pretty much intact?

Failing that, could one have formed anywhere in the solar system?

I'd lean towards no for both questions, it'd require a large amount of carbon and comparatively little oxygen at Venus' orbit. There wouldn't be a way for just Venus to be oxygen poor whilst leaving the rest of the solar system the same that I can see.

 

[Chronos]

I can think of no reason carbon would be so preferentially distributed in our solar system. All the planets of the inner solar system [mars inward] have remarkably similar compositions. Assuming accretion was the principle process for planet 'building', this is perfectly logical.

 

[TMEubanks]

The atmosphere of Venus is almost entirely CO2, but Venus is (from spacecraft observations) compositionally very similar to the Earth, including its Carbon abundance. The crust + atmosphere of Venus contains almost the same amount of Carbon as does the crust + oceans + atmosphere of the Earth. It's just that on Venus, there are no oceans, and all of the crustal Carbon has been driven into the atmosphere. It is, as far as we can tell, exactly what would happen if you warmed the surface of the Earth to 460 C, boiling the Oceans away and burning all of the soil, limestone, marble, etc., into CO2, which then would go into the atmosphere. (The surface of Venus is mostly quartz (SiO2) and other mineral oxides; i.e., lots of Oxygen, little or no Carbon.)

So, there is no reason, from the spacecraft exploration of Venus, to believe it is a Carbon planet, and excellent reasons to conclude that it isn't.

 

[twofish-quant]

It's not obvious to me how this it could work, but it depends on why you are asking the question. If you are writing a science fiction story, then having a carbon planet is less fantastic than having warp drive or humanoid aliens.

The problem is that that we don't know the exact details of planetary formation largely because it's only in the last few decades that we've started seeing exoplanets, and some of them are weird. So if someone turns up a pure carbon planet, that would be weird but not shocking. A pure carbon star would be shocking.

 

[TMEubanks]

@twofish-quant -

"Carbon planets" have been proposed as a possibility for stellar systems that form in carbon dominated molecular clouds. Some stars are carbon rich, and some interstellar clouds have enough carbon to absorb all of the Oxygen in CO and allow for the existence of substantial amounts of other carbon molecules (which is how we detect their carbon richness). So, it is reasonable to expect that some Earth-sized planets might have crusts dominated by Silicon Carbide and not Silicon Dioxide, possibly with a lot of carbonaceous material on the surface.

See http://arxiv.org/abs/astro-ph/0504214 for more details. Note that he talks about a proposal that the seed for Jupiter may have been a Carbon planet.

I agree about the sci-fi possibilities. If you want it, go for it. I just don't think it's plausible for the actual Venus.

If a Carbon planet had enough water to make oceans (which most may not), then they might have "floating continents" as some carbon compounds are lighter than water. That also would have interesting sci-fi possibilities (such as continental drift on a matter of months, not millions of years).