  We explore terrestrial planet formation with a focus on the supply of
solid-state organics as the main source of volatile carbon. For the water-poor
Earth, the water ice line, or ice sublimation front, within the planet-forming
disk has long been a key focal point. We posit that the soot line, the location
where solid-state organics are irreversibly destroyed, is also a key location
within the disk. The soot line is closer to the host star than the water
snowline and overlaps with the location of the majority of detected exoplanets.
In this work, we explore the ultimate atmospheric composition of a body that
receives a major portion of its materials from the zone between the soot line
and water ice line. We model a silicate-rich world with 0.1% and 1% carbon by
mass with variable water content. We show that as a result of geochemical
equilibrium, the mantle of these planets would be rich in reduced carbon but
have relatively low water (hydrogen) content. Outgassing would naturally yield
the ingredients for haze production when exposed to stellar UV photons in the
upper atmosphere. Obscuring atmospheric hazes appear common in the exoplanetary
inventory based on the presence of often featureless transmission spectra
(Kreidberg et al. 2014, Knutson et al. 2014, Libby-Roberts et al. 2020). Such
hazes may be powered by the high volatile content of the underlying
silicate-dominated mantle. Although this type of planet has no solar system
counterpart, it should be common in the galaxy with potential impact on
habitability.
