Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

A D/H ratio consistent with Earth’s water in Halley-type comet 12P from ALMA HDO mapping

Nature Astronomy (2025)Cite this article

Subjects

Abstract

Isotopic measurements of Solar System bodies provide a primary paradigm within which to understand the origins and histories of planetary materials. The deuterium-to-hydrogen (D/H) ratio, in particular, helps reveal the relationship between (and heritage of) different H2O reservoirs within the Solar System. Here we present interferometric maps of water (H2O) and semiheavy water (HDO) in the gas-phase coma of a comet (Halley-type comet 12P/Pons–Brooks), obtained using the Atacama Large Millimeter/submillimeter Array. The maps are consistent with outgassing of both H2O and HDO directly from the nucleus, and they imply a coma D/H ratio (for water) of (1.71 ± 0.44) × 10−4. This is at the lower end of the range of previously observed values in comets and is consistent with D/H in Earth’s ocean water. Our results indicate a possible common heritage between a component of the water ice reservoir in the Oort cloud and the water that was delivered to the young Earth during the early history of the Solar System.

Access through your institution
Buy or subscribe

This is a preview of subscription content, access via your institution

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: ALMA emission (integrated flux) maps of H2O and HDO in comet 12P/Pons–Brooks.
Fig. 2: Interferometric data for H2O and HDO in comet 12P.
Fig. 3: Comparison of D/H ratios in different bodies.

Similar content being viewed by others

Data availability

This work makes use of ALMA dataset ADS/JAO.ALMA#2023.1.01143.L, which is available for download from the ALMA Science Archive (https://almascience.nrao.edu/aq/). The IRTF iSHELL data, including all necessary science and calibration files, can be accessed from the IRTF Data Archive (https://irtfweb.ifa.hawaii.edu/research/irtf_data_archive.php).

Code availability

The SUBLIME radiative transfer model required to reproduce the results of this study is available for download from https://bitbucket.org/mcordiner/sublimed/src/master. The IRTF data reduction codes are available from https://github.com/nasapsg. The infrared telluric and cometary emission models are available through the PSG (https://psg.gsfc.nasa.gov).

References

  1. Lyons, J. R. & Young, E. D. CO self-shielding as the origin of oxygen isotope anomalies in the early solar nebula. Nature 435, 317–320 (2005).

    Article  Google Scholar 

  2. Furuya, K. et al. Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O. Astron. Astrophys. 599, A40 (2017).

    Article  Google Scholar 

  3. Visser, R. et al. Nitrogen isotope fractionation in protoplanetary disks. Astron. Astrophys. 615, A75 (2018).

    Article  Google Scholar 

  4. Nomura, H. et al. The isotopic links from planet forming regions to the Solar System. In Proc. Astronomical Society of the Pacific Conference Series, Vol. 534 (eds Inutsuka, S. et al.) 1075–1099 (ASP, 2023).

  5. Cleeves, L. I. et al. The ancient heritage of water ice in the Solar System. Science 345, 1590–1593 (2014).

    Article  Google Scholar 

  6. Meech, K. & Raymond, S. N. in Planetary Astrobiology (eds Meadows, V. S. et al.) 325–356 (Univ. Arizona Press, 2020).

  7. Marty, B. The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth Planet. Sci. Lett. 313, 56–66 (2012).

    Article  Google Scholar 

  8. Alexander, C. M. O., McKeegan, K. D. & Altwegg, K. Water reservoirs in small planetary bodies: meteorites, asteroids, and comets. Space Sci. Rev. 214, 36 (2018).

    Article  Google Scholar 

  9. Eberhardt, P., Reber, M., Krankowsky, D. & Hodges, R. R. The D/H and 18O/16O ratios in water from comet P/Halley. Astron. Astrophys. 302, 301–316 (1995).

    Google Scholar 

  10. Brown, R. H., Lauretta, D. S., Schmidt, B. & Moores, J. Experimental and theoretical simulations of ice sublimation with implications for the chemical, isotopic, and physical evolution of icy objects. Planet. Space Sci. 60, 166–180 (2012).

    Article  Google Scholar 

  11. Villanueva, G. L. et al. A sensitive search for deuterated water in comet 8P/Tuttle. Astrophys. J. Lett. 690, L5–L9 (2009).

    Article  Google Scholar 

  12. Meier, R. et al. A determination of the HDO/H2O ratio in comet C/1995 O1 (Hale-Bopp). Science 279, 842–844 (1998).

    Article  Google Scholar 

  13. Bockelée-Morvan, D. et al. Deuterated water in comet C/1996 B2 (Hyakutake) and its implications for the origin of comets. Icarus 133, 147–162 (1998).

    Article  Google Scholar 

  14. Lis, D. C. et al. Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets. Astron. Astrophys. 625, L5 (2019).

    Article  Google Scholar 

  15. Biver, N. et al. Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy). Astron. Astrophys. 589, A78 (2016).

    Article  Google Scholar 

  16. Levison, H. F. in Completing the Inventory of the Solar System (eds Rettig, T. & Hahn, J. M.) 173–191 (ASP, 1996).

  17. Nesvorný, D. et al. Origin and evolution of short-period comets. Astrophys. J. 845, 27 (2017).

    Article  Google Scholar 

  18. Cordiner, M. A. et al. Gas sources from the coma and nucleus of comet 46P/Wirtanen observed using ALMA. Astrophys. J. 953, 59 (2023).

    Article  Google Scholar 

  19. Hama, T., Kouchi, A. & Watanabe, N. Statistical ortho-to-para ratio of water desorbed from ice at 10 kelvin. Science 351, 65–67 (2016).

    Article  Google Scholar 

  20. Cordiner, M. A. et al. Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array. Astrophys. J. Lett. 792, L2 (2014).

    Article  Google Scholar 

  21. Roth, N. X. et al. Leveraging the ALMA Atacama Compact Array for cometary science: an interferometric survey of comet C/2015 ER61 (PanSTARRS) and evidence for a distributed source of carbon monosulfide. Astrophys. J. 921, 14 (2021).

    Article  Google Scholar 

  22. Mandt, K. E. et al. A nearly terrestrial D/H for comet 67P/Churyumov-Gerasimenko. Sci. Adv. 10, eadp2191 (2024).

    Article  Google Scholar 

  23. Rodgers, S. D. & Charnley, S. B. A model of the chemistry in cometary comae: deuterated molecules. Mon. Not. R. Astron. Soc. 330, 660–674 (2002).

    Article  Google Scholar 

  24. Hartogh, P. et al. Ocean-like water in the Jupiter-family comet 103P/Hartley 2. Nature 478, 218–220 (2011).

    Article  Google Scholar 

  25. Massey, F. J. The Kolmogorov-Smirnov test for goodness of fit. J. Am. Stat. Assoc. 46, 68–78 (1951).

    Article  Google Scholar 

  26. Willacy, K. The chemistry of multiply deuterated molecules in protoplanetary disks. I. The outer disk. Astrophys. J. 660, 441–460 (2007).

    Article  Google Scholar 

  27. Albertsson, T., Semenov, D. & Henning, T. Chemodynamical deuterium fractionation in the early solar nebula: the origin of water on Earth and in asteroids and comets. Astrophys. J. 784, 39 (2014).

    Article  Google Scholar 

  28. Ceccarelli, C. et al. in Protostars and Planets VI (eds Beuther, H. et al.) 859–882 (Univ. Arizona Press, 2014).

  29. Taquet, V., Charnley, S. B. & Sipilä, O. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores. Astrophys. J. 791, 1 (2014).

    Article  Google Scholar 

  30. Eistrup, C., Walsh, C. & van Dishoeck, E. F. Molecular abundances and C/O ratios in chemically evolving planet-forming disk midplanes. Astron. Astrophys. 613, A14 (2018).

    Article  Google Scholar 

  31. Tsiganis, K., Gomes, R., Morbidelli, A. & Levison, H. F. Origin of the orbital architecture of the giant planets of the Solar System. Nature 435, 459–461 (2005).

    Article  Google Scholar 

  32. Millar, T. J., Bennett, A. & Herbst, E. Deuterium fractionation in dense interstellar clouds. Astrophys. J. 340, 906–920 (1989).

    Article  Google Scholar 

  33. Meier, R. et al. Deuterium in comet C/1995 O1 (Hale-Bopp): detection of DCN. Science 279, 1707–1710 (1998).

    Article  Google Scholar 

  34. Müller, D. R. et al. High D/H ratios in water and alkanes in comet 67P/Churyumov-Gerasimenko measured with Rosetta/ROSINA DFMS. Astron. Astrophys. 662, A69 (2022).

    Article  Google Scholar 

  35. Garrod, R. T., Widicus Weaver, S. L. & Herbst, E. Complex chemistry in star-forming regions: an expanded gas-grain warm-up chemical model. Astrophys. J. 682, 283–302 (2008).

    Article  Google Scholar 

  36. Biver, N. et al. Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy). Sci. Adv. 1, 1500863 (2015).

    Article  Google Scholar 

  37. CASA Team. et al. CASA, the Common Astronomy Software Applications for radio astronomy. Publ. Astron. Soc. Pac. 134, 114501 (2022).

    Article  Google Scholar 

  38. Remijan, A., Seifert, N. A. & McGuire, B. A. The Database for Astronomical Spectroscopy – updates, additions and plans for Splatalogue for ALMA full science operations. In Proc. 71st International Symposium on Molecular Spectroscopy (eds McCall, B., McCall, B. & Polfer, N.) FB11 (University of Illinois, 2016).

  39. Cordiner, M. A. et al. A SUBLIME 3D model for cometary coma emission: the hypervolatile-rich comet C/2016 R2 (PanSTARRS). Astrophys. J. 929, 38 (2022).

    Article  Google Scholar 

  40. Ferellec, L. et al. Coma composition and profiles of comet 12P/Pons-Brooks using long-slit spectroscopy. Mon. Not. R. Astron. Soc. 534, 1816–1826 (2024).

    Article  Google Scholar 

  41. van der Tak, F. F. S., Lique, F., Faure, A., Black, J. H. & van Dishoeck, E. F. The Leiden Atomic and Molecular Database (LAMDA): current status, recent updates, and future plans. Atoms 8, 15 (2020).

    Article  Google Scholar 

  42. Mandal, B., Zoltowski, M., Cordiner, M., Lique, F. & Babikov, D. Rotational state-to-state transition rate coefficients for H2O + H2O collisions at nonequilibrium conditions. Astron. Astrophys. 688, A208 (2024).

    Article  Google Scholar 

  43. Crovisier, J. Rotational and vibrational synthetic spectra of linear parent molecules in comets. Astron. Astrophys. Suppl. Ser. 68, 223–258 (1987).

    Google Scholar 

  44. Bockelée-Morvan, D. et al. Herschel measurements of the D/H and 16O/18O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd). Astron. Astrophys. 544, L15 (2012).

    Article  Google Scholar 

  45. Biver, N. et al. Spectroscopic monitoring of comet C/1996 B2 (Hyakutake) with the JCMT and IRAM Radio Telescopes. Astron. J. 118, 1850–1872 (1999).

    Article  Google Scholar 

  46. Itikawa, Y. Rotational transition in an asymmetric-top molecule by electron collision: applications to H2O and H2CO. J. Phys. Soc. Jpn 32, 217–226 (1972).

    Article  Google Scholar 

  47. Hartogh, P. et al. HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd). Astron. Astrophys. 518, L150 (2010).

    Article  Google Scholar 

  48. Biver, N. et al. Long-term monitoring of the outgassing and composition of comet 67P/Churyumov-Gerasimenko with the Rosetta/MIRO instrument. Astron. Astrophys. 630, A19 (2019).

    Article  Google Scholar 

  49. Villanueva, G. L., Smith, M. D., Protopapa, S., Faggi, S. & Mandell, A. M. Planetary Spectrum Generator: an accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets. J. Quant. Spectrosc. Radiat. Transf. 217, 86–104 (2018).

    Article  Google Scholar 

  50. Huebner, W. F. & Mukherjee, J. Photoionization and photodissociation rates in solar and blackbody radiation fields. Planet. Space Sci. 106, 11–45 (2015).

    Article  Google Scholar 

  51. Newville, M. et al. LMFIT: Non-linear least-square minimization and curve-fitting for Python. Astrophysics Source Code Library ascl:1606.014 (2016).

  52. Lammerzahl, P. et al. Expansion velocity and temperatures of gas and ions measured in the coma of comet p/ Halley. Astron. Astrophys. 187, 169 (1987).

    Google Scholar 

  53. Tseng, W. L., Bockelée-Morvan, D., Crovisier, J., Colom, P. & Ip, W. H. Cometary water expansion velocity from OH line shapes. Astron. Astrophys. 467, 729–735 (2007).

    Article  Google Scholar 

  54. Tenishev, V., Combi, M. & Davidsson, B. A global kinetic model for cometary comae: the evolution of the coma of the Rosetta target comet Churyumov-Gerasimenko throughout the mission. Astrophys. J. 685, 659–677 (2008).

    Article  Google Scholar 

  55. Shou, Y. et al. A new 3D multi-fluid model: a study of kinetic effects and variations of physical conditions in the cometary coma. Astrophys. J. 833, 160 (2016).

    Article  Google Scholar 

  56. Cordiner, M. A. & Charnley, S. B. Neutral-neutral synthesis of organic molecules in cometary comae. Mon. Not. R. Astron. Soc. 504, 5401–5408 (2021).

    Article  Google Scholar 

  57. Haser, L. Distribution d’intensité dans la tête d’une comète. Bull. Classe Sci. Acad. R. Belg. 43, 740–750 (1957).

    MathSciNet  Google Scholar 

  58. DiSanti, M. A. et al. Hypervolatiles in a Jupiter-family comet: observations of 45P/Honda-Mrkos-Pajdušáková using iSHELL at the NASA-IRTF. Astron. J. 154, 246 (2017).

    Article  Google Scholar 

  59. Villanueva, G. L. et al. Water in planetary and cometary atmospheres: H2O/HDO transmittance and fluorescence models. J. Quant. Spectrosc. Radiat. Transf. 113, 202–220 (2012).

    Article  Google Scholar 

  60. Villanueva, G. L., DiSanti, M. A., Mumma, M. J. & Xu, L.-H. A quantum band model of the ν3 fundamental of methanol (CH3OH) and its application to fluorescence spectra of comets. Astrophys. J. 747, 37 (2012).

    Article  Google Scholar 

  61. DiSanti, M. A., Bonev, B. P., Villanueva, G. L. & Mumma, M. J. Highly depleted ethane and mildly depleted methanol in comet 21P/Giacobini-Zinner: application of a new empirical ν2-band model for CH3OH near 50 K. Astrophys. J. 763, 1 (2013).

    Article  Google Scholar 

  62. Bonev, B. P. Towards a Chemical Taxonomy of Comets: Infrared Spectroscopic Methods for Quantitative Measurements of Cometary Water. PhD thesis, Univ. Toledo (2005).

  63. Xie, X. & Mumma, M. J. Monte Carlo simulation of cometary atmospheres: application to comet P/Halley at the time of the Giotto spacecraft encounter. I. Isotropic model. Astrophys. J. 464, 442 (1996).

    Article  Google Scholar 

  64. Cheng, Y. C. et al. Water ortho-to-para ratio in the coma of comet 67P/Churyumov-Gerasimenko. Astron. Astrophys. 663, A43 (2022).

    Article  Google Scholar 

  65. Bonev, B. P. et al. A search for variation in the H2O ortho-para ratio and rotational temperature in the inner coma of comet C/2004 Q2 (Machholz). Astrophys. J. Lett. 661, L97–L100 (2007).

    Article  Google Scholar 

  66. Bonev, B. P. et al. Evidence for two modes of water release in comet 103P/Hartley. 2. Distributions of column density, rotational temperature, and ortho-para ratio. Icarus 222, 740–751 (2013).

    Article  Google Scholar 

  67. Villanueva, G. L. et al. The molecular composition of Comet C/2007 W1 (Boattini): evidence of a peculiar outgassing and a rich chemistry. Icarus 216, 227–240 (2011).

    Article  Google Scholar 

  68. Faure, A. et al. The ortho-to-para ratio of water in interstellar clouds. Mon. Not. R. Astron. Soc. 487, 3392–3403 (2019).

    Article  Google Scholar 

  69. De Lucia, F. C., Cook, R. L., Helminger, P. & Gordy, W. Millimeter and submillimeter wave rotational spectrum and centrifugal distortion effects of HDO. J. Chem. Phys. 55, 5334–5339 (1971).

    Article  Google Scholar 

  70. Kisiel, Z. & Kraśnicki, A. The millimetre-wave rotational spectrum of phenylacetylene. J. Mol. Spectrosc. 262, 82–88 (2010).

    Article  Google Scholar 

  71. Nixon, C. A. et al. Isotopic ratios in Titan’s methane: measurements and modeling. Astrophys. J. 749, 159 (2012).

    Article  Google Scholar 

Download references

Acknowledgements

This work was supported by NASA’s Planetary Science Division Internal Scientist Funding Program through the Fundamental Laboratory Research (FLaRe) work package. E.L.G. was supported by the NSF (Grant No. AST-2009910). B.P.B. was supported by the NSF (Grant No. AST-2009398) and NASA (SSO Grant No. 80NSSC22K1401). K.F. was supported by the JSPS (KAKENHI Grant No. 20H05847). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (Contract No. 80NM0018D0004). D.C.L. acknowledges financial support from the NASA Astrophysics Data Analysis Program. ALMA is a partnership of ESO, NSF (USA), NINS (Japan), NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. We thank M. R. Combi for sharing 12P water production rates derived from SOHO/SWAN observations, and for helpful discussions on the radial dependence of coma outflow velocities. E.L.G., B.P.B. and N.X.R. are visiting astronomers at the IRTF, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate and grateful to have the opportunity to conduct IRTF observations from this mountain.

Author information

Authors and Affiliations

  1. Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    M. A. Cordiner, N. X. Roth, S. B. Charnley, M. Jin & S. N. Milam

  2. Department of Physics, Catholic University of America, Washington, DC, USA

    M. A. Cordiner & M. Jin

  3. Department of Mathematics, Physics, Astronomy, and Statistics, University of Missouri-St Louis, St Louis, MO, USA

    E. L. Gibb

  4. Institute of Physics, Polish Academy of Sciences, Warsaw, Poland

    Z. Kisiel

  5. Department of Physics, American University, Washington, DC, USA

    N. X. Roth & B. P. Bonev

  6. LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris Cité, Meudon, France

    N. Biver, D. Bockelée-Morvan & J. Crovisier

  7. IRAM, Saint Martin d’Hères, France

    J. Boissier

  8. East Asian Observatory, Hilo, HI, USA

    I. M. Coulson

  9. Physikalish-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC), Davos Dorf, Switzerland

    M. N. Drozdovskaya

  10. RIKEN Pioneering Research Institute, Wako-shi, Japan

    K. Furuya

  11. Center of Astronomy and Gravitation, and Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan, ROC

    Y.-J. Kuan

  12. INAF - Osservatorio astrofisico di Arcetri, Florence, Italy

    M. Lippi

  13. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    D. C. Lis

  14. Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK

    C. Opitom

  15. Institute for Astrophysical Research, Boston University, Boston, MA, USA

    C. Qi

  16. National Radio Astronomy Observatory, Charlottesville, VA, USA

    A. J. Remijan

Authors
  1. M. A. Cordiner
    View author publications

    Search author on:PubMed Google Scholar

  2. E. L. Gibb
    View author publications

    Search author on:PubMed Google Scholar

  3. Z. Kisiel
    View author publications

    Search author on:PubMed Google Scholar

  4. N. X. Roth
    View author publications

    Search author on:PubMed Google Scholar

  5. N. Biver
    View author publications

    Search author on:PubMed Google Scholar

  6. D. Bockelée-Morvan
    View author publications

    Search author on:PubMed Google Scholar

  7. J. Boissier
    View author publications

    Search author on:PubMed Google Scholar

  8. B. P. Bonev
    View author publications

    Search author on:PubMed Google Scholar

  9. S. B. Charnley
    View author publications

    Search author on:PubMed Google Scholar

  10. I. M. Coulson
    View author publications

    Search author on:PubMed Google Scholar

  11. J. Crovisier
    View author publications

    Search author on:PubMed Google Scholar

  12. M. N. Drozdovskaya
    View author publications

    Search author on:PubMed Google Scholar

  13. K. Furuya
    View author publications

    Search author on:PubMed Google Scholar

  14. M. Jin
    View author publications

    Search author on:PubMed Google Scholar

  15. Y.-J. Kuan
    View author publications

    Search author on:PubMed Google Scholar

  16. M. Lippi
    View author publications

    Search author on:PubMed Google Scholar

  17. D. C. Lis
    View author publications

    Search author on:PubMed Google Scholar

  18. S. N. Milam
    View author publications

    Search author on:PubMed Google Scholar

  19. C. Opitom
    View author publications

    Search author on:PubMed Google Scholar

  20. C. Qi
    View author publications

    Search author on:PubMed Google Scholar

  21. A. J. Remijan
    View author publications

    Search author on:PubMed Google Scholar

Contributions

All authors helped write the telescope observing proposals, checked and validated the data analysis methods, and edited the paper. M.A.C. performed the data reduction and radiative transfer modelling, generated the figures and wrote the text of the paper. E.L.G. performed the IRTF observations, data reduction and analysis. B.P.B. investigated the IRTF H2O OPR. Z.K. performed the HDO laboratory spectroscopy.

Corresponding author

Correspondence to M. A. Cordiner.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks Michal Drahus, Michiel Hogerheijde and Youssef Moulane for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Observed ALMA spectrum of comet 12P.

These data were observed using ALMA on 2024 April 18-25, and show the comet’s spectrum in the vicinity of the HDO 21,1 − 21,2 and CH3OH JK = 5K − 4K lines (labeled). The (continuum-subtracted) spectrum was extracted at the position of the continuum emission peak (the assumed location of the nucleus), and molecular lines were assigned using data from the Splatalogue (https://splatalogue.online/)39. Inset panel shows a zoom of the detected HDO line.

Extended Data Fig. 2 ALMA emission maps of CH3OH in comet 12P.

The data, observed in Band 6 (between 2024 April 18-25; left) and Band 5 (2024 May 4; right), have been spectrally integrated, continuum-subtracted, and are centered on the thermal continuum peak. The Band 6 image is integrated over 14 transitions, with a contour separation of 10σ, while the Band 5 image is integrated over 8 transitions, with 5σ contours (see Supplementary Table 2 for details). Inset panels (upper right) show the spectral line profiles of selected transitions as a function of cometocentric velocity (v), extracted at the origin (8 lines in the Band 5 CH3OH spectrum have been averaged in velocity space, to improve the signal-to-noise rato). The spatial resolution (beam FWHM) is shown lower left, and the directions of the (sky-projected) comet-Sun and orbital trail vectors are shown lower right.

Extended Data Fig. 3 Coma kinetic temperature radial profiles.

Temperatures were retrieved independently on the HDO and H2O observation dates dates using multi-line ALMA CH3OH observations. 1σ error envelopes are shown.

Extended Data Fig. 4 ALMA interferometric spectra of H2O and HDO.

The real part of the observed visibility data is shown as a function of frequency for H2O (left) and HDO (right), averaged across the antenna baseline range uv=12-100 m (corresponding to angular scales on the sky <24” for H2O and <21” for HDO). Best-fit SUBLIME radiative transfer models (see Table 1 and Figure 2 for details), are overlaid in red.

Extended Data Fig. 5 ALMA interferometric spectra of CH3OH (average of observations in the date range 18–25 April 2024).

The real parts of the observed visibility spectra are shown as a function of baseline interval, averaged within the uv range specified in each panel (corresponding to angular sizes θ in the plane of the sky). The best-fit SUBLIME radiative transfer model is overlaid in red.

Extended Data Fig. 6 ALMA interferometric spectra of CH3OH (observed 4 May 2024).

The real parts of the observed visibility spectra are shown as a function of baseline interval, averaged within the uv range specified in each panel (corresponding to angular sizes θ in the plane of the sky). The best-fit SUBLIME radiative transfer model is overlaid in red.

Extended Data Table 1 IRTF Measurements
Full size table

Supplementary information

Supplementary Information

Supplementary Tables 1–3 and Fig. 1.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Cordiner, M.A., Gibb, E.L., Kisiel, Z. et al. A D/H ratio consistent with Earth’s water in Halley-type comet 12P from ALMA HDO mapping. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02614-7

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-025-02614-7

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing