Carbon-grain sublimation: a new top-down component of protostellar
  chemistry
  Earth's carbon deficit has been an outstanding problem in our understanding
of the formation of our Solar System. A possible solution would be the
sublimation of carbon grains at the so-called soot line (~300 K) early in the
planet-formation process. Here, we argue that the most likely signatures of
this process are an excess of hydrocarbons and nitriles inside the soot line,
and a higher excitation temperature for these molecules compared to
oxygen-bearing complex organics that desorb around the water snowline (~100 K).
Such characteristics have been reported in the literature, for example, in
Orion KL, although not uniformly, potentially due to differences in
observational settings and analysis methods of different studies or related to
the episodic nature of protostellar accretion. If this process is active, this
would mean that there is a heretofore unknown component to the carbon chemistry
during the protostellar phase that is acting from the top down - starting from
the destruction of larger species - instead of from the bottom up from atoms.
In the presence of such a top-down component, the origin of organic molecules
needs to be re-explored.
