Grey planet

More speculation on the formation of carbon planets: the soot layer.

Bergin et al. seem unaffiliated with Allen-Sutter's al. - to the point the late article doesn't even cite Allen-Sutter. In fact some distance is placed inasmuch as Bergin's proposed planet is 0.1%–1% in mass; so not diamond-dominate.

Bergin's soot layer is the distance between a (here defined) soot line and the ice line which Bergin places (reasonably) at ~170 K. In our solar-system the ice line is, I think, 4 AU; Ceres itself formed outside that, migrating inward and simply keeping most its ice. Earth and Venus and even Mars formed in the rock line; with Earth at least getting much of its water also from outward, and later.

Bergin has carbonaceous chondrites' organics roaming around C₁₀₀H_75–79O_11–17N_3–4S_1–3. This interplanetary coal doesn't dissolve; but inside the soot line, with the rocky worlds, it will decompose. Such organics thrive somewhere around where Ceres is at; past Ceres, such will be mixed with ice. Bergin counts 67P as a comet but I am happy considering it a Cereslike. Most sooty-ice asteroids should lose ice like a comet; Ceres saving its water, by being heavy.

The soot line is ~500 K which is far hotter than Earth gets now. But when the inner planets were forming, with Sol as a T Tauri and with protoplanets crashing into earth other down here, that 500 K line was easily crossed.

The hazy grey planet, effectively a superTitan, is alien to the extent Bergin's crew cannot envision a biocycle. I've considered possibilities such a planet might have formed instead of Mars, in our own system (although it didn't). I must however question if it gets enough insolation/flux.

BACKDATE 5/27. UPDATE 10/20: At terrestrial-planet temperatures and below, Uranus might be Type A and Earth, B. Type C is - you guessed it - carbon-dominant. David Moore ponders K2-18's sulfur in such a matrix.

CLOUDS 1/10/24: I've been pondering carbondioxide as vapour. This liquifies only under high pressure, so lower in the atmosphere than what we'd see from water. The planet would also have to be cold. It also needs an oxygen-source to burn off methane - this much, at least, can happen when water ice is irradiated, as the Jovians from Europa-on-out.