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:

Detection of HCN and diverse redox chemistry in the plume of Enceladus

Nature Astronomy volume 8, pages 164–173 (2024)Cite this article

Subjects

Abstract

The Cassini spacecraft observed that Saturn’s moon Enceladus has a series of jets erupting from its South Polar Terrain. Previous studies of in situ data collected by Cassini’s Ion and Neutral Mass Spectrometer (INMS) have identified H2O, CO2, CH4, NH3 and H2 within the plume of ejected material. Identification of minor species in the plume remains an ongoing challenge, owing to the large number of possible combinations that can be used to fit the INMS data. Here we present the detection of several additional compounds of strong importance to the habitability of Enceladus, including HCN, C2H2, C3H6 and C2H6. Our analyses of the low-velocity INMS data, coupled with our detailed statistical framework, enable discrimination between previously ambiguous species in the plume by alleviating the effects of high-dimensional model fitting. Together with plausible mineralogical catalysts and redox gradients derived from surface radiolysis, these compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life.

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

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

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

Fig. 1: Previously unidentified compounds in the Enceladus plume indicate a potentially habitable environment.
Fig. 2: Model performance as a function of model complexity.
Fig. 3: Average low-velocity INMS spectrum and reconstructed model fit.
Fig. 4: Contributions of individual species to the model fit.

Similar content being viewed by others

Data availability

All INMS REU spectra are publicly available from the Planetary Data System at https://doi.org/10.17189/1519605. All NIST spectra are publicly available from the NIST Chemistry WebBook at https://doi.org/10.18434/T4D303.

Code availability

The code for this work was implemented using open-source Python libraries available at https://pypi.org/ and is available upon request.

References

  1. Dougherty, M. K. et al. Identification of a dynamic atmosphere at Enceladus with the Cassini magnetometer. Science 311, 1406–1409 (2006).

  2. Porco, C. C. et al. Cassini observes the active south pole of Enceladus. Science 311, 1393–1401 (2006).

  3. Hansen, C. J. et al. Water vapour jets inside the plume of gas leaving Enceladus. Nature 456, 477–479 (2008).

  4. Waite, J. H. et al. Cassini finds molecular hydrogen in the Enceladus plume: evidence for hydrothermal processes. Science 356, 155–159 (2017).

  5. Waite Jr, J. H. et al. Liquid water on Enceladus from observations of ammonia and 40Ar in the plume. Nature 460, 487–490 (2009).

  6. Waite, J. H. et al. Cassini Ion and Neutral Mass Spectrometer: Enceladus plume composition and structure. Science 311, 1419–1422(2006).

  7. Hillier, J. K. et al. The composition of Saturn’s E ring. Mon. Not. R. Astron. Soc. 377, 1588–1596 (2007).

  8. Postberg, F., Schmidt, J., Hillier, J., Kempf, S. & Srama, R. A salt-water reservoir as the source of a compositionally stratified plume on Enceladus. Nature 474, 620–622 (2011).

  9. Postberg, F. et al. Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus. Nature 459, 1098–1101 (2009).

  10. Postberg, F. et al. The E-ring in the vicinity of Enceladus: II. Probing the moon’s interior—the composition of E-ring particles. Icarus 193, 438–454 (2008).

  11. Combe, J.-P. et al. Nature, distribution and origin of CO2 on Enceladus. Icarus 317, 491–508 (2019).

  12. Postberg, F. et al. Macromolecular organic compounds from the depths of Enceladus. Nature 558, 564–568 (2018).

  13. James, G., Witten, D., Hastie, T. & Tibshirani, R. (eds) An Introduction to Statistical Learning: with Applications in R Springer Texts in Statistics No. 103 (Springer, 2013).

  14. Chandrasekaran, B. & Jain, A. Quantization complexity and independent measurements. IEEE Trans. Comput. C-23, 102–106 (1974).

  15. Hughes, G. On the mean accuracy of statistical pattern recognizers. IEEE Trans. Inf. Theory 14, 55–63 (1968).

  16. Trunk, G. V. A problem of dimensionality: a simple example. IEEE Trans. Pattern Anal. Mach. Intell. PAMI-1, 306–307 (1979).

  17. Guyon, I. & Elisseeff, A. An introduction to variable and feature selection. J. Mach. Learn. Res. 3, 1157–1182 (2003).

  18. Cui, J. et al. Analysis of Titan’s neutral upper atmosphere from Cassini Ion Neutral Mass Spectrometer measurements. Icarus 200, 581–615 (2009).

  19. Magee, B. A. et al. INMS-derived composition of Titan’s upper atmosphere: analysis methods and model comparison. Planet. Space Sci. 57, 1895–1916 (2009).

  20. Waite, J. H. et al. Ion Neutral Mass Spectrometer results from the first flyby of Titan. Science 308, 982–986 (2005).

  21. Waite, J. H. et al. The process of tholin formation in Titan’s upper atmosphere. Science 316, 870–875 (2007).

  22. Waite, J. H. et al. Chemical interactions between Saturn’s atmosphere and its rings. Science 362, eaat2382 (2018).

    Article  ADS  PubMed  Google Scholar 

  23. Akaike, H. Information theory and an extension of the maximum likelihood principle. In Proc. 2nd International Symposium on Information Theory (eds. Petrov, B. N. & Csaki, F.) 267–281 (Akademiai Kiado, 1973).

  24. Hurvich, C. M. & Tsai, C.-L. Regression and time series model selection in small samples. Biometrika 76, 297–307 (1989).

  25. Sakamoto, Y., Ishiguro, M. & Kitagawa, G. Akaike Information Criterion Statistics (KTK Scientific Publishers, 1986).

  26. Sugiura, N. Further analysts of the data by Akaike’s information criterion and the finite corrections. Commun. Stat. Theory Methods 7, 13–26 (1978).

  27. Burnham, K. P. & Anderson, D. R. (eds) Model Selection and Multimodel Inference (Springer, 2004).

  28. Akaike, H. On the likelihood of a time series model. Statistician 27, 217–235 (1978).

  29. Kullback, S. & Leibler, R. A. On information and sufficiency. Ann. Math. Stat. 22, 79–86 (1951).

  30. Johnson, J. B. & Omland, K. S. Model selection in ecology and evolution. Trends Ecol. Evol. 19, 101–108 (2004).

  31. Richards, S. A. Dealing with overdispersed count data in applied ecology: overdispersed count data. J. Appl. Ecol. 45, 218–227 (2007).

  32. Richards, S. A., Whittingham, M. J. & Stephens, P. A. Model selection and model averaging in behavioural ecology: the utility of the IT-AIC framework. Behav. Ecol. Sociobiol. 65, 77–89 (2011).

  33. Richards, S. A. Testing ecological theory using the information-theoretic approach: examples and cautionary results. Ecology 86, 2805–2814 (2005).

  34. Postberg, F. et al. in Enceladus and the Icy Moons of Saturn (ed. Schenk, P.) 129–162 (Univ. Arizona Press, 2018).

  35. Jaramillo-Botero, A. et al. Hypervelocity impact effect of molecules from Enceladus’ plume and Titan’s upper atmosphere on NASA’s Cassini spectrometer from reactive dynamics simulation. Phys. Rev. Lett. 109, 213201 (2012).

    Article  ADS  PubMed  Google Scholar 

  36. Smith, H. T. et al. Enceladus: a potential source of ammonia products and molecular nitrogen for Saturn’s magnetosphere: Saturn’s magnetospheric nitrogen sources. J. Geophys. Res. Space Phys. https://doi.org/10.1029/2008JA013352 (2008).

  37. Bockelée-Morvan, D., Crovisier, J., Mumma, M. J. & Weaver, H. A. in Comets II (eds Festou, M. et al.) 391–423 (Univ. Arizona Press, 2004).

  38. Mumma, M. J. & Charnley, S. B. The chemical composition of comets—emerging taxonomies and natal heritage. Ann. Rev. Astron. Astrophys. 49, 471–524 (2011).

  39. Newburn, R. L., Neugebauer, M. & Rahe, J. (eds) Comets in the Post-Halley Era: In Part Based on Reviews Presented at the 121st Colloquium of the International Astronomical Union, Held in Bamberg, Germany, April 24–28, 1989 Astrophysics and Space Science Library, Vol. 167 (Springer, 1991).

  40. Johnson, R. E. & Quickenden, T. I. Photolysis and radiolysis of water ice on outer Solar System bodies. J. Geophys. Res. Planets 102, 10985–10996 (1997).

  41. Affholder, A., Guyot, F., Sauterey, B., Ferrière, R. & Mazevet, S. Bayesian analysis of Enceladus’s plume data to assess methanogenesis. Nat. Astron. 5, 805–814 (2021).

  42. Hoehler, T. M. Implications of H2/CO2 disequilibrium for life on Enceladus. Nat. Astron. 6, 3–4 (2022).

  43. Oremland, R. S. & Voytek, M. A. Acetylene as fast food: implications for development of life on anoxic primordial Earth and in the outer Solar System. Astrobiology 8, 45–58 (2008).

  44. Colby, J., Dalton, H. & Whittenbury, R. Biological and biochemical aspects of microbial growth on C1 compounds. Ann. Rev. Microbiol. 33, 481–517 (1979).

  45. Yurimoto, H., Kato, N. & Sakai, Y. Assimilation, dissimilation, and detoxification of formaldehyde, a central metabolic intermediate of methylotrophic metabolism. Chem. Rec. 5, 367–375 (2005).

  46. Singh, R., Guzman, M. S. & Bose, A. Anaerobic oxidation of ethane, propane, and butane by marine microbes: a mini review. Front. Microbiol. 8, 2056 (2017).

    Article  PubMed  PubMed Central  Google Scholar 

  47. Russell, M. J. & Nitschke, W. Methane: fuel or exhaust at the emergence of life? Astrobiology 17, 1053–1066 (2017).

  48. Zolotov, M. Y. A model for low-temperature biogeochemistry of sulfur, carbon, and iron on Europa. J. Geophys. Res. 109, E06003 (2004).

    ADS  Google Scholar 

  49. Ray, C. et al. Oxidation processes diversify the metabolic menu on Enceladus. Icarus 364, 114248 (2021).

    Article  CAS  Google Scholar 

  50. Miller, S. L. The mechanism of synthesis of amino acids by electric discharges. Biochim. Biophys. Acta 23, 480–489 (1957).

  51. Orgel, L. E. Prebiotic chemistry and the origin of the RNA world. Crit. Rev. Biochem. Molecul. Biol. 39, 99–123 (2004).

  52. Oró, J. & Kimball, A. P. Synthesis of purines under possible primitive earth conditions. I. Adenine from hydrogen cyanide. Arch. Biochem. Biophys. 94, 217–227 (1961).

  53. Patel, B. H., Percivalle, C., Ritson, D. J., Duffy, C. D. & Sutherland, J. D. Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism. Nat. Chem. 7, 301–307 (2015).

  54. Miyakawa, S., Cleaves, H. J. & Miller, S. L. The cold origin of life: A. Implications based on the hydrolytic stabilities of hydrogen cyanide and formamide. Orig. Life Evol. Biosph. 32, 195–208 (2002).

  55. Miller, S. L. & Orgel, L. E. The Origins of Life on the Earth Concepts of Modern Biology Series (Prentice-Hall, 1974).

  56. Levy, M., Miller, S. L., Brinton, K. & Bada, J. L. Prebiotic synthesis of adenine and amino acids under Europa-like conditions. Icarus 145, 609–613 (2000).

  57. Hand, K. P. On the Physics and Chemistry of the Ice Shell and Sub-surface Ocean of Europa. PhD thesis, Stanford Univ. (2007).

  58. Hand, K. P., Carlson, R. W. & Tsapin, A. I. Laboratory analysis of water, hydrocarbon and ammonia ice mixtures exposed to high-energy electron irradiation. Bull. Am. Astron. Soc. 38, 606 (2006).

  59. Hand, K. P., Chyba, C. F., Priscu, J. C., Carlson, R. W. & Nealson, K. H. in Europa (eds Pappalardo, R. T. et al.) 589–630 (Univ. Arizona Press, 2009).

  60. Hsu, H.-W. et al. Ongoing hydrothermal activities within Enceladus. Nature 519, 207–210 (2015).

  61. Glein, C. R., Postberg, F. & Vance, S. D. in Enceladus and the Icy Moons of Saturn (ed. Schenk, P.) 39–56 (Univ. Arizona Press, 2018).

  62. McKay, C. P., Davila, A., Glein, C. R., Hand, K. & Stockton, A. M. in Enceladus and the Icy Moons of Saturn (ed. Schenk, P.) 37–452 (Univ. Arizona Press, 2018).

  63. Zolotov, M. Y. et al. Chemical and phase composition of Enceladus: insights from Cassini data. In European Planetary Science Conference EPSC-DPS2011-1330 (2011).

  64. Matson, D. L., Castillo, J. C., Lunine, J. & Johnson, T. V. Enceladus’ plume: compositional evidence for a hot interior. Icarus 187, 569–573 (2007).

  65. Foustoukos, D. I. & Seyfried, W. E. Hydrocarbons in hydrothermal vent fluids: the role of chromium-bearing catalysts. Science 304, 1002–1005 (2004).

  66. Proskurowski, G. et al. Abiogenic hydrocarbon production at Lost City hydrothermal field. Science 319, 604–607 (2008).

  67. Blöchl, E., Keller, M., Wachtershäuser, G. & Stetter, K. O. Reactions depending on iron sulfide and linking geochemistry with biochemistry. Proc. Natl Acad. Sci. USA 89, 8117–8120 (1992).

  68. Wächtershäuser, G. Before enzymes and templates: theory of surface metabolism. Microbiol. Rev. 52, 452–484 (1988).

  69. Benner, S. A. et al. When did life likely emerge on Earth in an RNA first process? ChemSystemsChem https://doi.org/10.1002/syst.201900035 (2020).

  70. Sasselov, D. D., Grotzinger, J. P. & Sutherland, J. D. The origin of life as a planetary phenomenon. Sci. Adv. 6, eaax3419 (2020).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  71. Powner, M. W., Gerland, B. & Sutherland, J. D. Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature 459, 239–242 (2009).

  72. Waite, J. H. et al. The Cassini Ion and Neutral Mass Spectrometer (INMS) investigation. Space Sci. Rev. 114, 113–231 (2004).

  73. Miller, K. et al. Cassini INMS constraints on the composition and latitudinal fractionation of Saturn ring rain material. Icarus 339, 113595 (2020).

    Article  CAS  Google Scholar 

  74. Hansen, C. J. et al. Enceladus’ water vapor plume. Science 311, 1422–1425 (2006).

  75. Brown, R. H. et al. Composition and physical properties of Enceladus’ surface. Science 311, 1425–1428 (2006).

  76. Teolis, B. D. et al. A revised sensitivity model for Cassini INMS: results at Titan. Space Sci. Rev. 190, 47–84 (2015).

  77. Fitch, W. L. & Sauter, A. D. Calculation of relative electron impact total ionization cross sections for organic molecules. Anal. Chem. 55, 832– 835 (1983).

  78. Graves, V., Cooper, B. & Tennyson, J. Calculated electron impact ionisation fragmentation patterns. J. Phys. B 54, 235203 (2021).

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

We thank J. H. Waite and B. A. Magee for their help on interpreting INMS instrument effects. J.S.P. thanks M. Sako and K. L. Wagstaff for useful discussions and statistical insight, and D. D. Sasselov for helpful discussions on prebiotic chemistry. All authors acknowledge the support of the Cassini Data Analysis Program (NNN13D466T) and the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). T.A.N. was also supported by an appointment to the NASA Postdoctoral Fellowship Program at the Jet Propulsion Laboratory administered by Oak Ridge Associated Universities and Universities Space Research Association through a contract with NASA. K.P.H. also acknowledges support from the NASA Astrobiology Program (80NSSC19K1427) and the Europa Lander Pre-Project, managed by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Author information

Authors and Affiliations

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

    Jonah S. Peter, Tom A. Nordheim & Kevin P. Hand

  2. Biophysics Program, Harvard University, Boston, MA, USA

    Jonah S. Peter

Authors
  1. Jonah S. Peter
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Tom A. Nordheim
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kevin P. Hand
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

J.S.P., T.A.N. and K.P.H. contributed to the conceptual development of the study, to the interpretation of results and to the final version of the paper. J.S.P. developed the methodology, performed the mathematical analysis and wrote the first version of the paper.

Corresponding author

Correspondence to Jonah S. Peter.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks Christelle Briois and Brian Magee 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 Full mass range INMS spectrum and analysis of residuals.

(a) The black silhouette shows the full mass range of the INMS spectrum used in this work. Shaded gray bars indicate count values at 1 and 2 u that were omitted from this work (see Methods). The spectrum was adapted from ref. 12. Error bars show 1σ Gaussian uncertainty in the observed count rates. The minimum count uncertainty was estimated as ~ 2 counts from the count rates of noisy mass channels at masses >46 u. Red circles show the reconstructed model fit based on the mixing ratios of Extended Data Table 2. (b) Scatterplot of the standardized residuals produced by fitting the model. Only mass channels with counts above the minimum uncertainty are shown. There is no discernable pattern amongst the residuals or evidence of heteroscedasticity. (c) Histogram of the standardized residuals (red bars) compared to a reference Gaussian distribution with zero mean (black curve). The residuals show good agreement with the Gaussian distribution, indicating a robust model fit. The black arrow indicates a potential outlier at mass 16, which likely results from the standardization of the slow flyby count rates at neighboring mass channels.

Extended Data Fig. 2 Comparison of model performance without HCN.

Blue circles show the maximum relative likelihoods across all models for each value of d species (as in Fig. 2a). Red diamonds indicate the highest likelihood models without HCN. All models without HCN exhibit exceptionally poor performance, with a maximum relative likelihood peaking at λ = 6.1 × 10−4 for d = 12.

Extended Data Table 1 Complete list of compounds included in the analysis
Full size table
Extended Data Table 2 Modeling results for the complete spectral library
Full size table

Supplementary information

Supplementary Information

Supplementary Figs. 1–4, Tables 1 and 2, Results and Discussion.

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

Peter, J.S., Nordheim, T.A. & Hand, K.P. Detection of HCN and diverse redox chemistry in the plume of Enceladus. Nat Astron 8, 164–173 (2024). https://doi.org/10.1038/s41550-023-02160-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-023-02160-0

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