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OH as a probe of the warm-water cycle in planet-forming disks

Nature Astronomy (2024)Cite this article

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Abstract

Water is a key ingredient for the emergence of life as we know it. Yet, its destruction and reformation in space remain unprobed in warm gas (T > 300 K). Here we detect with the James Webb Space Telescope the emission of the hydroxyl radical (OH) from d203-506, a planet-forming disk exposed to external far-ultraviolet (FUV) radiation. These observations were made as part of the Early Release Science programme PDRs4All, which is focused on the Orion bar. The observed OH spectrum is compared with the results of quantum dynamical calculations to reveal two essential molecular processes. The highly excited rotational lines of OH in the mid-infrared are telltale signs of H2O destruction by FUV radiation. The OH rovibrational lines in the near-infrared are attributed to chemical excitation by the key reaction O + H2 → OH + H, which seeds the formation of water in the gas phase. These results show that under warm and irradiated conditions, water is destroyed and efficiently reformed through gas-phase reactions. We infer that, in this source, the equivalent of Earth oceans’ worth of water is destroyed per month and replenished. This warm-water cycle could reprocess some water inherited from cold interstellar clouds and explain the lower deuterium fraction of water in Earth’s oceans compared with that found around protostars.

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Fig. 1: JWST NIRCam composite image of the Orion bar in the Orion molecular cloud.
Fig. 2: Evidence for H2O photodissociation from OH rotational lines detected by MIRI-MRS.
Fig. 3: Evidence for formation pumping through O + H2 from OH rovibrational lines detected by NIRSpec.

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Data availability

The JWST data presented in this paper are publicly available through the MAST online archive (http://mast.stsci.edu) using the PID 1288. The MIRI-MRS and NIRSpec spectra presented in Figs. 2 and 3 and Extended Data Fig. 8 are available in ASCII format at https://doi.org/10.5281/zenodo.10634184.

Code availability

The JWST pipeline used to produce the final data products presented in this article is available at https://github.com/spacetelescope/jwst. The GROSBETA code used in this study is available from the corresponding author on reasonable request.

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Acknowledgements

This work is based (in part) on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programme ERS1288. This work was supported by the French National Centre for Space Studies (CNES) with funds focused on JWST. This research has been supported by the Programme National Physique et Chimie du Milieu Interstellaire of the French National Centre for Scientific Research and the French National Institute for Earth Sciences and Astronomy with INC (Institut de Chimie)/INP (Institut de Physique) co-funded by the French Alternative Energies and Atomic Energy Commission and CNES. J.R.G. thanks the Spanish Ministry of Science, Innovation and Universities (MCINN) for funding support (Grant No. PID2019-106110GB-I00). A.Z. acknowledges funding from Grant Nos. PID2019-107115GB-C21 and PID2021-122549NB-C21. E.v.D. acknowledges support from the European Research Council (Advanced Grant No. 101019751 MOLDISK). E.V., M.M., L.G.S. and F.J.A. acknowledge funding from MCINN (Grant No. PID2021-122839NB-I00). L.G.S., P.G.J. and A.V. acknowledge funding from MCINN (Grant No. PID2020-113147GA-I00). A.V. also acknowledges support from the Junta Castilla y León and European Social Fund (Grant No. EDU/1508/2020). This work is sponsored (in part) by the Chinese Academy of Sciences (CAS), through a grant to the CAS South America Center for Astronomy in Santiago, Chile. D.v.d.P. acknowledges support for programme 1288 provided by NASA through a grant from the Space Telescope Science Institute. C.B. is grateful for an appointment at NASA Ames Research Center through the San José State University Research Foundation (Grant No. 80NSSC22M0107) and acknowledges support from the Internal Scientist Funding Model of the Laboratory Astrophysics Directed Work Package at NASA Ames. A.F. is grateful to MCINN for funding (Grant No. PID2019-106235GB-I00) and to the European Research Council for funding (Advanced Grant Project SUL4LIFE, Grant Agreement No. 101096293). Work by Y.O. and M. Röllig is carried out within the Collaborative Research Centre 956, subproject C1, funded by the German Research Foundation (Project ID 184018867). E.P. and J.C. acknowledge support from the University of Western Ontario, the Institute for Earth and Space Exploration, CSA and the Natural Sciences and Engineering Research Council of Canada. T.O. acknowledges support from a bilateral programme of the Japan Society for the Promotion of Science (Grant No. 120219939). This research made use of pdrtpy, the PhotoDissociation Region Toolbox, an open-source model for photodissociation regions and a data analysis package43,44,45,46.

Author information

Authors and Affiliations

  1. Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, Orsay, France

    Marion Zannese, Benoît Tabone, Emilie Habart, Boris Trahin, Alain Abergel, Meriem Elyajouri, Olga Kannavou, Raphael Meshaka & Thiébaut Schirmer

  2. Instituto de Física Fundamental (CSIC), Madrid, Spain

    Javier R. Goicoechea & Alexandre Zanchet

  3. Leiden Observatory, Leiden University, Leiden, The Netherlands

    Ewine F. van Dishoeck & Alexander G. G. M. Tielens

  4. Max-Planck Institut für Extraterrestrische Physik (MPE), Garching, Germany

    Ewine F. van Dishoeck

  5. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands

    Marc C. van Hemert

  6. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden

    John H. Black & Thiébaut Schirmer

  7. Astronomy Department, University of Maryland, College Park, MD, USA

    Alexander G. G. M. Tielens & Mark G. Wolfire

  8. Departamento de Química Física, University of Salamanca, Salamanca, Spain

    A. Veselinova, P. G. Jambrina & L. Gonzalez-Sanchez

  9. Departamento de Química Física (Unidad Asociada al CSIC), Universidad Complutense de Madrid, Ciudad Universitaria, Madrid, Spain

    M. Menendez, E. Verdasco & F. J. Aoiz

  10. Institut des Sciences Moléculaires d’Orsay, CNRS, Université Paris-Saclay, Orsay, France

    Emmanuel Dartois

  11. Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III - Paul Sabatier, CNRS, CNES, Toulouse, France

    Olivier Berné, Ilane Schroetter, Amélie Canin, Lina Issa & Christine Joblin

  12. Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

    Els Peeters, Ameek Sidhu, Ryan Chown, Jan Cami, Baria Khan, Sofia Pasquini & Bethany Schefter

  13. Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, Canada

    Els Peeters, Ameek Sidhu, Ryan Chown, Jan Cami & Bethany Schefter

  14. Carl Sagan Center, SETI Institute, Mountain View, CA, USA

    Els Peeters & Jan Cami

  15. Yunnan Observatories, Chinese Academy of Sciences, Kunming, China

    Jinhua He

  16. Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing, China

    Jinhua He

  17. Departamento de Astronomica, Universidad de Chile, Santiago, Chile

    Jinhua He

  18. Space Telescope Science Institute, Baltimore, MD, USA

    Dries Van De Putte, Karl D. Gordon & Massimo Robberto

  19. Department of Astronomy, University of Michigan, Ann Arbor, MI, USA

    Felipe Alarcón, Edwin A. Bergin & Marc W. Pound

  20. ACRI-ST, Centre d’Etudes et de Recherche de Grasse (CERGA), Grasse, France

    Jeronimo Bernard-Salas

  21. INCLASS Common Laboratory, Grasse, France

    Jeronimo Bernard-Salas

  22. NASA Ames Research Center, Moffett Field, CA, USA

    Christiaan Boersma & Alexandros Maragkoudakis

  23. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, Meudon, France

    Emeric Bron, David Languignon & Raphael Meshaka

  24. UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK

    Daniel Dicken

  25. Centro de Astrobiología, CAB, CSIC-INTA, Madrid, Spain

    Asunción Fuente

  26. Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium

    Karl D. Gordon

  27. Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes, CNRS, Grenoble, France

    Romane Le Gal

  28. Institut de Radioastronomie Millimétrique (IRAM), Saint-Martin d’Hères, France

    Romane Le Gal

  29. I. Physikalisches Institut der Universität zu Köln, Cologne, Germany

    Yoko Okada & Markus Röllig

  30. Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo, Japan

    Takashi Onaka

  31. Department of Physics, Faculty of Science and Engineering, Meisei University, Tokyo, Japan

    Takashi Onaka

  32. Johns Hopkins University, Baltimore, MD, USA

    Massimo Robberto

  33. Physikalischer Verein - Gesellschaft für Bildung und Wissenschaft, Frankfurt, Germany

    Markus Röllig

  34. Institut für Angewandte Physik, Frankfurt, Germany

    Markus Röllig

  35. Instituto de Astrofísica e Ciências do Espaço, Lisbon, Portugal

    Sílvia Vicente

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  1. Marion Zannese
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  11. P. G. Jambrina
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  12. M. Menendez
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  14. F. J. Aoiz
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  15. L. Gonzalez-Sanchez
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Contributions

M.Z., B. Tabone, E.H. and A.Z. wrote the paper with input from J.R.G., E.v.D., A.T., E.B. and J.H. M.Z. and B. Tabone did the line analysis with support from A.Z. and J.H.B. using the quantum dynamical calculations of M.C.v.H., A.V., P.G.J., M.M., E.V., F.J.A. and L.G.S. I.S., A.C., R.C., A.S., B. Trahin, F.A. and D.V.P. reduced the data. E.H., E.P. and O.B. planned and co-led the ERS PDRs4All programme. B. Tabone, J.R.G., A.T., B. Trahin, E.D., A.A., F.A., E.B., J.B.S., C.B., E.A.B., J.C., A.C., R.C., D.D., M.E., A.F., K.D.G., L.I., C.J., O.K., B.K., D.L., R.L.G., A.M., R.M., Y.O., T.O., S.P., M.W.P., M. Robberto, M. Röllig, B.S., T.S., I.S., A.S., D.v.d.P., S.V. and M.G.W. contributed to the observing programme with JWST. All authors participated in the development and testing of the MIRI-MRS or NIRSpec instruments and their data reduction, participated in discussing the results or commented on the paper.

Corresponding author

Correspondence to Marion Zannese.

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Nature Astronomy thanks Jenny Calahan and Thomas Haworth for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Spatial distribution of the emission of key lines.

(Top Left) d203-506 image from the NIRCam F212N filter (in MJy sr−1), (Top Right) NIRSpec integrated intensity map of the OH line at 2.934 μm (in erg cm−2s−1sr−1), (Bottom Left) MIRI-MRS integrated intensity map of the OH line at 9.791 μm (in erg cm−2s−1sr−1), (Bottom Right) integrated intensity map of the [OI] line at 0.63 μm obtained from the Hubble Space Telescope (HST) (in counts s−1)28. The NIRSpec H2 1-0 S(1) intensity map is shown in white contours (at 7 × 10−4, 2 × 10−3 erg cm−2s−1sr−1).

Extended Data Fig. 2 Processing steps of the MIRI-MRS and NIRSpec spectra to better visualize the OH lines.

(a) (Top panel) Spectrum observed with MIRI-MRS. The red line is the estimated continuum. (Middle panel) Continuum subtracted spectrum. The red Gaussians are the fits to lines other than OH. The blue Gaussians are the fits to lines from the OFF position which contaminate OH lines. (Bottom panel) Processed spectrum with the dust continuum and the bright lines other than OH subtracted. (b) (Top panel) Spectrum observed with NIRSpec. The red line is the estimated continuum. (Middle panel) Continuum subtracted spectrum. The red Gaussians are fits to lines other than OH. (Bottom panel) Processed spectrum with the dust continuum and the bright lines other than OH subtracted.

Extended Data Fig. 3 Schematic view of OH spectroscopy relevant to JWST.

(a) OH rotational and ro-vibrational energy levels. The red arrows are the pure rotational transitions observable with MIRI-MRS. The blue arrows are some of the ro-vibrational transitions observable with NIRSpec. (b) Zoom-in on the yellow box to reveal the splitting of a rotational level due to the spin-orbit coupling and the Λ-doubling. The two spin-orbit states are labeled by the Ω quantum number and the Λ-doubling states are labeled by their ϵ = e / f spectroscopic parity. The green and pink arrows are the transitions detected in the observations forming a quadruplet. The green arrows are the transitions arising from symmetric states and the pink arrows are the transitions arising from antisymmetric states.

Extended Data Fig. 4 Excitation diagram of H2 at the bright spot.

The temperature fit was made on the first five pure rotational lines. The measured line fluxes are reported in Extended Data Table 2. The uncertainties are calculated by the Python routine curve_fit as 1σ errors on the parameters. The impact of calibration effects is not taken into account and the associated uncertainties can be as high as 20%.

Extended Data Fig. 5 Excitation diagram of ro-vibrational and pure rotational lines of OH.

The blue crosses are the ro-vibrational transitions detected with NIRSpec (v=1-0) and the red crosses are the pure rotational transitions detected with MIRI-MRS (v=0-0). The measured line fluxes are reported in Extended Data Table 1. The uncertainties are calculated by the Python routine curve_fit as 1σ errors on the parameters. The impact of calibration effects is not taken into account and the associated uncertainties can be as high as 20%.

Extended Data Fig. 6 State distributions of nascent OH predicted by quantum dynamical calculations summed over the spin-orbit and Λ-doubling states.

(Left) Distribution of nascent OH following its formation via O+H2 at a temperature of T = 1, 000 K and for a H2 population as inferred for d203-506. (Right) Distribution of nascent OH following H2O photodissociation by a FUV field representative of the Orion Bar. Photodissociation by short wavelength photons λ<144 nm via the \(\tilde{{{{{B}}}}}\) electronic state of water produces rotationally hot OH with rotational quantum numbers of N ≃ 35 − 45 and photodissociation by longer wavelength photons via the \(\tilde{{{{{A}}}}}\) electronic state leads to rotationally cold but vibrationally hot OH.

Extended Data Fig. 7 Comparison between the observed OH near-IR emission and modeling of excitation processes other than formation-pumping.

OH near-IR synthetic GROSBETA models for (Top) UV radiative pumping and (Bottom) H2O photodissociation via its \(\tilde{{{{{A}}}}}\) electronic state. None of these processes can account for the shape and strength of the observed OH ro-vibrational spectrum.

Extended Data Fig. 8 MIRI-MRS observations versus a synthetic RADEX spectrum of the brightest H2O lines.

MIRI-MRS observations versus a synthetic RADEX55 spectrum of the brightest H2O lines adopting the maximum amount of unseen water of N(H2O) = 5 × 1015cm−2 as inferred from the mid-IR lines of OH, a temperature of T =1000K as inferred from H2 lines and a density of nH = 107 cm−3 as inferred from the near-IR lines of OH. Inelastic collisional rate coefficients are from ref. 64 and are available on the LAMDA database65. We also assumed an IR background inferred from NIRSpec and MIRI-MRS observations. When calculating the line intensities, we assumed that the IR continuum background interacting with the gas is not along the same line of sight as the observations as described in ref. 21. The latter assumption provides a strict upper limit on the line strength. Owing to the low gas density, H2O is subthermally excited, leading to undetectable lines. In the 5-7 μm region, the MIRI-MRS spectrum is affected by residual fringe and possible contamination by \({{{{{\rm{CH}}}}}_{3}}^{+}\)52. An LTE model at T = 700K of \({{{{{\rm{CH}}}}}_{3}}^{+}\) is overlayed in grey66 for reference. In the 18-24 μm, the residual fringe increases due to the increase in the continuum, making the detection of H2O lines in this region impossible. The same model of H2O multiplied by a factor of 10 is overlayed in purple.

Extended Data Table 1 Intensities of the OH lines detected at the bright spot with MIRI-MRS and NIRSpec
Full size table
Extended Data Table 2 Intensities of the H2 lines detected at the bright spot with MIRI-MRS and NIRSpec
Full size table

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Zannese, M., Tabone, B., Habart, E. et al. OH as a probe of the warm-water cycle in planet-forming disks. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02203-0

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