The effect of carbon grain destruction on the chemical structure of protoplanetary disks

Chen-En Wei, Hideko Nomura, Jeong-Eun Lee, Wing-Huen Ip, Catherine Walsh, T. J. Millar

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)
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The bulk composition of 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 (PPDs) 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 H 2O and CO 2, are depleted. We compare the results of these model calculations with the solid carbon-to-silicon 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 the asteroid belt and a lower value at the location of Earth. In addition, using the obtained molecular abundance distributions, coupled with line radiative transfer calculations, we make predictions for ALMA to potentially observe the effect of carbon grain destruction in nearby PPDs. The results indicate that HCN, H 13CN, and c-C 3H 2 may be good tracers.

Original languageEnglish
Article number129
Number of pages21
JournalThe Astrophysical Journal
Issue number2
Early online date16 Jan 2019
Publication statusPublished - 16 Jan 2019

Bibliographical note

31 pages, 21 figures, Accepted for publication in The Astrophysical Journal


  • astro-ph.EP

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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