The Effect of Carbon Grain Destruction On The Chemical Structure of Protoplanetary Disks

©NASA

Protoplanetary Disk

The bulk composition of the Earth is dramatically carbon poor compared to that of the interstellar medium, and this phenomenon extends to the asteroid belt.

To interpret this carbon deficit problem, the carbonaceous component in grains must have been converted into the gas-phase in the inner regions of protoplanetary disks prior to planetary formation. We examine the effect of carbon grain destruction on the chemical structure of disks by calculating the molecular abundances and distributions using a comprehensive chemical reaction network. When carbon grains are destroyed and the elemental abundance of the gas becomes carbon-rich, the abundances of carbon-bearing molecules, such as HCN and carbon-chain molecules, increase dramatically near the midplane, while oxygen-bearing molecules, such as H2O and CO2, are depleted. We compare the results of these model calculations with the solid carbon fraction in the solar system.

Although we find a carbon depletion gradient, there are some quantitative discrepancies: the model shows a higher value at the position of asteroid belt and a lower value at the location of the Earth. In addition, using the obtained molecular abundances distributions, coupled with line radiative transfer calculations, we make predictions for ALMA to potentially observe the effect of carbon grain destruction in nearby protoplanetary disks. The results indicate that HCN, H13CN and c-C3H2 may be good tracers.

Chen-En Wei, Hideko Nomura, Jeong-Eun Lee, Wing-Huen Ip, Catherine Walsh, T. J. Millar
(Submitted on 26 Nov 2018)

Comments: 31 pages, 21 figures, Accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1811.10194 [astro-ph.EP] (or arXiv:1811.10194v1 [astro-ph.EP] for this version)
Submission history
From: Chenen Wei
[v1] Mon, 26 Nov 2018 06:13:10 UTC (4,215 KB)
https://arxiv.org/abs/1811.10194
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