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A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects

Nature Astronomy volume 9, pages 230–244 (2025)Cite this article

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Abstract

The detection of molecules on the coldest and outermost objects in our Solar System has long been limited by the terrestrial atmosphere and sensitivity of the available instrumentation. However, near-infrared observations by the James Webb Space Telescope have provided an unprecedented view of the molecular diversity on the surfaces of trans-Neptunian objects (TNOs). Using the low spectral resolution PRISM mode on the near-infrared spectrograph as part of the Cycle 1 large programme, ‘Discovering the Surface Composition of trans-Neptunian objects’, we report the detection of several molecular ices throughout the TNO population, including H2O, CO2, 13CO2, CO, CH3OH and complex molecules and refractory materials containing aliphatic C–H, C≡N, O–H and N–H bonds. As a result of the imprint that these molecules leave on the spectra, three main compositional groups consistently emerge from multiple independent cluster analyses. Our results unlock the long-standing question of the interpretation of colour diversity, providing the much-needed compositional information. The marked separation of the three spectral clusters reveals sharp variations in the surface molecular constituents. The C/O and (CH + NH)/(C + O) ratios on the surface of TNOs are the primary indicators of the spectral differences among the three TNO compositional groups observed. We propose that these objects are fossil remnants of icy planetesimals, and that the three compositional groups provide a picture of the ice retention lines in the Solar System that likely occurred in the outer protoplanetary disk, possibly just before a major planetary migration.

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Fig. 1: Physical and orbital parameters of the DiSCo sample of TNOs.
Fig. 2: Results of the PCA and k-means clustering technique.
Fig. 3: Representative spectra of each compositional class of TNOs.
Fig. 4: Distribution of molecules between compositional groups.
Fig. 5: Ice line hypothesis in relation to the molecules dominating each compositional group.

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Data availability

The JWST data used in this analysis are publicly available from the STScI MAST Archive (https://doi.org/10.17909/r2zp-r280).

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Acknowledgements

The DiSCo-TNOs team would like to thank W. Eck and A. Henry of the Space Telescope Science Institute (STScI) for their help in preparing the observations for execution. This study was based on observations made with the National Aeronautics and Space Administration/European Space Agency/Canadian Space Agency JWST under the GO-1 programme 2418. Support for this programme was provided by NASA through a grant from STScI. The data were obtained from the Barbara A. Mikulski Archive for Space Telescopes at the STScI, which is operated by the Association of Universities for Research in Astronomy, under the NASA contract NAS 5-03127 for JWST. N.P.-A. acknowledges the Ministry of Science, Innovation, and Universities (MCIU) in Spain and the State Agency for Research (AEI) for funding through the ATRAE programme, project ATR2023-145683. R.B. and E.H. acknowledge the support from the CNES-France (JWST mission). N.P. acknowledges funding by Fundação para a Ciência e a Tecnologia through the research grants UIDB/04434/2020 and UIDP/04434/2020. J.A.S. acknowledges the Lowell Observatory and Northern Arizona University, both in Flagstaff, AZ, for their support during his sabbatical tenure. J.L. acknowledges support from the ACIISI, Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund under grant ProID2021010134, and support from the Agencia Estatal de Investigacion del Ministerio de Ciencia e Innovacion under grant ‘Hydrated Minerals and Organic Compounds in Primitive Asteroids’ with reference PID2020-120464GB-100.

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Authors and Affiliations

  1. Florida Space Institute, University of Central Florida, Orlando, FL, USA

    Noemí Pinilla-Alonso, Mário N. De Prá, Ana Carolina de Souza Feliciano, Charles A. Schambeau & Brittany Harvison

  2. Institute of Space Science and Technology of Asturias (ICTEA), Universidad de Oviedo, Oviedo, Spain

    Noemí Pinilla-Alonso

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

    Rosario Brunetto & Elsa Hénault

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

    Bryan J. Holler, John A. Stansberry & Ian Wong

  5. Fundación Galileo Galilei-INAF, La Palma, Spain

    Vania Lorenzi

  6. Instituto de Astrofísica de Canarias, La Laguna, Spain

    Vania Lorenzi & Javier Licandro

  7. Department of Physics, University of Central Florida Orlando, FL, USA

    Yvonne J. Pendleton & Dale P. Cruikshank

  8. Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany

    Thomas G. Müller

  9. Northern Arizona University, Flagstaff, AZ, USA

    John A. Stansberry, Joshua P. Emery & Lucas McClure

  10. Lowell Observatory, Flagstaff, AZ, USA

    John A. Stansberry

  11. Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Spain

    Javier Licandro

  12. Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, CNRS UCBL, ENSL, Villeurbanne, France

    Aurélie Guilbert-Lepoutre

  13. Instituto de Astrofísica e Ciências do Espaço, Departamento de Física, Universidade de Coimbra, Coimbra, Portugal

    Nuno Peixinho

  14. Te Kura Matū School of Physical and Chemical Sciences, University of Canterbury Christchurch, New Zealand

    Michele T. Bannister

Authors
  1. Noemí Pinilla-Alonso
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  2. Rosario Brunetto
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  3. Mário N. De Prá
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  4. Bryan J. Holler
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  5. Elsa Hénault
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  6. Ana Carolina de Souza Feliciano
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  7. Vania Lorenzi
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  8. Yvonne J. Pendleton
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  9. Dale P. Cruikshank
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  10. Thomas G. Müller
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  11. John A. Stansberry
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  12. Joshua P. Emery
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  13. Charles A. Schambeau
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  14. Javier Licandro
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  15. Brittany Harvison
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  16. Lucas McClure
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  17. Aurélie Guilbert-Lepoutre
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  18. Nuno Peixinho
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  19. Michele T. Bannister
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  20. Ian Wong
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Contributions

N.P.-A., V.L., M.N.D.P., B.J.H. and J.A.S. designed the observational programme. N.P.-A., R.B., M.N.D.P., J.L., Y.J.P., D.P.C., T.G.M., J.A.S. and J.P.E. conceived the scientific goals of DiSCo. B.H., N.P.-A., I.W., A.C.d.S.F., M.N.D.P. and C.A.S. reduced and validated the data. N.P.-A., E.H., R.B., M.N.D.P., A.C.d.S.F., J.A.S. and T.G.M. performed the band identification and spectral characterization. R.B., M.N.D.P. and N.P.-A. performed clustering and studied the band areas. R.B., N.P.-A. and B.J.H. elaborated and proposed the scenario for interpreting the results. N.P.-A., R.B. and E.H. drafted the manuscript. All authors were involved in the discussion of the results and the finalization of the manuscript.

Corresponding author

Correspondence to Noemí Pinilla-Alonso.

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Nature Astronomy thanks Theodore Kareta and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Bowl-type DiSCo spectra.

All the spectra in the Bowl-type group normalized at 2.6 μm and shift vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.

Extended Data Fig. 2 Double Dip-type DiSCo spectra.

All the spectra in the Double-Dip-type group normalized at 2.6 μm and shift vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.

Extended Data Fig. 3 Cliff-type DiSCo spectra.

All the spectra in the Cliff-type group normalized at 2.6 μm and shift vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.

Extended Data Fig. 4 Unclassified DiSCo Spectra.

Spectra of objects in the DiSCo sample not included in the clustering corresponding, from top to bottom, to two low signal-to-noise observations, five Centaurs, and one object in the Haumea family. The Centaurs are studied in detail in20. The spectrum of 2013 UZ117 does not resemble any other object in the DiSCo sample but it is in agreement with the spectra of other objects in the Haumea family observed in program GTO-1191. Its peculiar shape resembles that of pure water ice making these objects the only water-ice-rich surfaces in the trans-Neptunian belt. Spectra have been normalized at 2.6 μm and shifted vertically for clarity. The light grey bars at each wavelength correspond to the standard deviation.

Extended Data Fig. 5 Hierarchical clustering on the DiSCo dataset.

The detection of three main spectral groups is evident using either a Euclidean (left) or cosine (right) distance metric.

Extended Data Fig. 6 Detail of absorption bands identified in DiSCo-TNOs spectra.

Panel A: median of each compositional group ± the median absolute deviation compared to the reflectance of pure crystalline water ice97 and a Tholin rich in C–H and N–H molecules98. In green the spectrum of Enceladus obtained with JWST64. Panel B: median of the Bowl-type spectra ± the median absolute deviation, Enceladus64, and pure crystalline water ice, all three showing the Fresnel Peak at 3.1 μm. Panel C: Spectra of Arrokoth29, from New Horizons, and two DiSCo-TNOs targets compared with the spectrum of methanol and a tholin rich in N–H and C–H molecules98. Panel D: Median spectra of the Double-Dip and Cliff-type TNOs ± the median absolute deviation compared to the reflectance of methanol and tholins98. Panel E: Spectra of two DiSCo-TNOs targets compared to the spectrum of methanol and H2S99. Panel F: Spectra of two DiSCo-TNO targets compared to the spectrum of Jupiter’s moon Callisto85 showing an absorption of C ≡ N and the spectra of 13CO2100, OCN − 101, and CO102.

Extended Data Fig. 7 Examples of calculations of band areas for four different objects.

Band A: CH3OH and organics; B: CO2; C: H2O; D: aliphatic C − − H. Error bars are provided for each spectrum (median absolute deviation over the 4-dithers within each wavelength bin), confirming these are significant detections. The three baseline calculations and corresponding areas are reported in dark gray for the linear baseline, gray for the second order polynomial function, and light gray for the third order polynomial function. See text for more details.

Extended Data Table 1 Observation circumstances
Full size table
Extended Data Table 2 Physical properties of the TNOs in the DiSCo program
Full size table
Extended Data Table 3 Summary of spectral attributions
Full size table

Supplementary information

Supplementary Information

Supplementary Figs. 1–3 and reference.

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Pinilla-Alonso, N., Brunetto, R., De Prá, M.N. et al. A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects. Nat Astron 9, 230–244 (2025). https://doi.org/10.1038/s41550-024-02433-2

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