Letter | Published:

The comet-like composition of a protoplanetary disk as revealed by complex cyanides

Nature volume 520, pages 198201 (09 April 2015) | Download Citation

Abstract

Observations of comets and asteroids show that the solar nebula that spawned our planetary system was rich in water and organic molecules. Bombardment brought these organics to the young Earth’s surface1. Unlike asteroids, comets preserve a nearly pristine record of the solar nebula composition. The presence of cyanides in comets, including 0.01 per cent of methyl cyanide (CH3CN) with respect to water, is of special interest because of the importance of C–N bonds for abiotic amino acid synthesis2. Comet-like compositions of simple and complex volatiles are found in protostars, and can readily be explained by a combination of gas-phase chemistry (to form, for example, HCN) and an active ice-phase chemistry on grain surfaces that advances complexity3. Simple volatiles, including water and HCN, have been detected previously in solar nebula analogues, indicating that they survive disk formation or are re-formed in situ4,5,6,7. It has hitherto been unclear whether the same holds for more complex organic molecules outside the solar nebula, given that recent observations show a marked change in the chemistry at the boundary between nascent envelopes and young disks due to accretion shocks8. Here we report the detection of the complex cyanides CH3CN and HC3N (and HCN) in the protoplanetary disk around the young star MWC 480. We find that the abundance ratios of these nitrogen-bearing organics in the gas phase are similar to those in comets, which suggests an even higher relative abundance of complex cyanides in the disk ice. This implies that complex organics accompany simpler volatiles in protoplanetary disks, and that the rich organic chemistry of our solar nebula was not unique.

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Acknowledgements

We acknowledge comments from E. van Dishoeck. This Letter makes use of ALMA data. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. K.I.Ö. acknowledges A. Leroy and the NAASC for assistance with calibration and imaging, and also acknowledges funding from the Simons Collaboration on the Origins of Life (SCOL), the Alfred P. Sloan Foundation, and the David and Lucile Packard Foundation. D.J.W. acknowledges funding from NASA Origins of Solar Systems (grant no. NNX11AK63).

Author information

Affiliations

  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA

    • Karin I. Öberg
    • , Viviana V. Guzmán
    • , Chunhua Qi
    • , Sean M. Andrews
    • , Ryan Loomis
    •  & David J. Wilner
  2. Leiden Observatory, Leiden University, PO Box 9513, 2300 CA Leiden, The Netherlands

    • Kenji Furuya
  3. Kobe University, 1-1 Rokkodaicho, Nada Ward, Kobe, Hyogo Prefecture 657-0013, Japan

    • Yuri Aikawa

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Contributions

K.I.Ö. led the overall project, reduced the data, assisted by V.V.G. and R.L., and wrote the manuscript with revisions from S.M.A. and D.J.W. V.V.G., assisted by C.Q., performed the parametric modelling and abundance extraction. K.F. performed the astrochemical modelling, and interpreted the results with Y.A. All authors contributed to discussions of the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Karin I. Öberg.

The ALMA program number for the presented data is 2013.1.00226.

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https://doi.org/10.1038/nature14276

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