Abstract
The surface of Ganymede exhibits diversity in composition, interpreted as indicative of geological age differences between dark and bright terrains. Observations from Galileo and Earth-based telescopes have revealed the presence of both water ice and non-ice material, indicative of either endogenic or exogenic processes, or some combination. However, these observations attained a spatial resolution that was too coarse to reveal the surface composition at a local scale. Here we present the high-spatial-resolution infrared spectra of Ganymede observed with the Jovian InfraRed Auroral Mapper onboard the National Aeronautics and Space Administration’s Juno spacecraft during a close flyby that occurred on 7 June 2021. We found that at a pixel resolution <1 km, the surface of Ganymede exhibits signatures diagnostic of hydrated sodium chloride, ammonium chloride and sodium/ammonium carbonate, as well as organic compounds, possibly including aliphatic aldehydes. Carbon dioxide shows up mostly at trailing longitudes. The composition and spatial distribution of these salts and organics suggest that their origin is endogenic, resulting from the extrusion of subsurface brines, whose chemistry reflects the water–rock interaction inside Ganymede.
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Data availability
The JIRAM dataset used for our analysis is publicly available at the Juno Archive of the Planetary Atmospheres Node (https://pds-atmospheres.nmsu.edu/PDS/data/PDS4/juno_jiram_bundle/data_calibrated/orbit34/). The filenames of the JIRAM spectroscopic data for Ganymede are listed in Table 1. Source data are provided with this paper64.
Code availability
The computer code used to produce I/F spectral profiles of Ganymede and to compute band depths is a direct implementation of the procedures described in the Methods section. Spectral unmixing with FCLS was carried out using PySptools, available at https://pysptools.sourceforge.io/. Spectral unmixing with MCMC is a direct implementation of the algorithm61. The computer code used to model the chemical speciation of NH3 and CO2 is a direct implementation of the SUPCRTBL code63.
References
Schenk, P. M. Thickness constraints on the icy shells of the Galilean satellites from a comparison of crater shapes. Nature 417, 419–421 (2002).
Saur, J. et al. The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals. J. Geophys. Res. Space Phys. 120, 1715–1737 (2015).
Carlson, R. W. et al. Near-infrared mapping spectrometer experiment on Galileo. Space Sci. Rev. 60, 457–502 (1992).
Stephan, K., Hibbitts, C. A. & Jaumann, R. H2O-ice particle size variations across Ganymede’s and Callisto’s surface. Icarus 337, 113440 (2020).
McCord, T. B. et al. Hydrated salt minerals on Ganymede’s surface: evidence of an ocean below. Science 292, 1523–1525 (2001).
McCord, T. B. et al. Hydrated salt minerals on Europa’s surface from the Galileo near-infrared mapping spectrometer (NIMS) investigation. J. Geophys. Res. 104, 11827–11852 (1999).
Ligier, N. et al. VLT/SINFONI observations of Europa: new insights into the surface composition. Astron. J. 151, 163 (2016).
Ligier, N. et al. Surface composition and properties of Ganymede: updates from ground-based observations with the near-infrared imaging spectrometer SINFONI/VLT/ESO. Icarus 333, 496–515 (2019).
Trumbo, S. K., Brown, M. E. & Hand, K. P. Sodium chloride on the surface of Europa. Sci. Adv. 5, aaw7123 (2019).
Adriani, A. et al. JIRAM, the Jovian Infrared Auroral Mapper. Space Sci. Rev. 213, 393–446 (2017).
Bolton, S. J. et al. The Juno mission. Science 356, 821–825 (2017).
Hansen, C. J. et al. Juno’s close encounter with Ganymede—An overview. Geophys. Res. Lett. 49, e2022GL099285 (2022).
Mura, A. et al. Infrared observations of Ganymede from the Jovian InfraRed Auroral Mapper on Juno. J. Geophys. Res. Planets 125, e2020JE006508 (2020).
Wang, F. et al. Laboratory and field characterization of visible to near-infrared spectral reflectance of nitrate minerals from the Atacama Desert, Chile, and implications for Mars. Am. Mineral. 103, 197–206 (2018).
De Angelis, S. et al. High temperature VIS-IR Spectroscopy of NH4 phyllosilicates. J. Geophys. Res. Planets 126, e06696 (2021).
Berg, B. L. et al. Reflectance spectroscopy (0.35–8 µm) of ammonium-bearing minerals and qualitative comparison to Ceres-like asteroids. Icarus 265, 218–237 (2016).
Ehlmann, B. L. et al. Ambient and cold-temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies. Meteorit. Planet. Sci. 53, 1884–1901 (2018).
Mastrapa, R. M. et al. Optical constants of amorphous and crystalline H2O-ice: 2.5–22 μm (4000–455 cm−1) optical constants of H2O-ice. Astrophys. J. 701, 1347–1356 (2009).
McCord, T. B. et al. Organics and other molecules in the surfaces of Callisto and Ganymede. Science 278, 271–275 (1997).
Socrates, G. Infrared and Raman Characteristic Group Frequencies: Tables and Charts (John Wiley & Sons, 2004); https://isbnsearch.org/isbn/978-0-470-09307-8
Moroz, L. V. et al. Natural solid bitumens as possible analogs for cometary and asteroid organics: 1. Reflectance spectroscopy of pure bitumens. Icarus 134, 253–268 (1998).
Ciarniello, M. et al. VIS-IR spectroscopy of mixtures of water ice, organic matter, and opaque mineral in support of small body remote sensing observations. Minerals 11, 1222 (2021).
Chaban, G. M. et al. Carbon dioxide on planetary bodies: theoretical and experimental studies of molecular complexes. Icarus 187, 592–599 (2007).
Carlson, R. W. et al. Hydrogen peroxide on the surface of Europa. Science 283, 2062–2064 (1999).
Carlson, R. W., Johnson, R. E. & Anderson, M. S. Sulfuric acid on Europa and the radiolytic sulfur cycle. Science 286, 97–99 (1999).
King, O. & Fletcher, L. N. Global modelling of Ganymede’s surface composition: near-IR mapping from VLT/SPHERE. J. Geophys. Res. Planets 127, e2022JE007323 (2022).
Trumbo, S. K. et al. Hydrogen peroxide at the poles of Ganymede. Sci. Adv. 9, eadg3724 (2023).
Nash, D. B. & Betts, B. H. Laboratory infrared spectra (2.3–23 µm) of SO2 phases: applications to Io surface analysis. Icarus 117, 402–419 (1995).
Douté, S. et al. Mapping SO2 frost on Io by the modeling of NIMS hyperspectral images. Icarus 149, 107–132 (2001).
Hibbitts, C. A., McCord, T. B. & Hansen, G. B. Distributions of CO2 and SO2 on the surface of Callisto. J. Geophys. Res. 105, 22,541–22,557 (2000).
Collins, G. C. et al. Global geologic map of Ganymede: Scientific Investigations Map 3237 (US Geological Survey, 2013); https://doi.org/10.3133/sim3237
Hibbitts, C. A. et al. Carbon dioxide on Ganymede. J. Geophys. Res. 108, 5036–5058 (2003).
Aponte, J. C. et al. Analyses of aliphatic aldehydes and ketones in carbonaceous chondrites. ACS Earth Space Chem. 3, 463–472 (2019).
Khawaja, N. et al. Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains. Mon. Not. R. Astron. Soc. 489, 5231–5243 (2019).
Grossmann, Y. et al. Aliphatic aldehydes in the Earth’s crust—Remains of prebiotic chemistry? Life 12, 925 (2022).
Liuzzo, L. et al. Variability in the energetic electron bombardment of Ganymede. J. Geophys. Res. Space Phys. 125, e28347 (2020).
Poppe, A. R. et al. Thermal and energetic ion dynamics in Ganymede’s magnetosphere. J. Geophys. Res. Space Phys. 123, 4614–4637 (2018).
Plainaki, C. et al. Kinetic simulations of the Jovian energetic ion circulation around Ganymede. Astrophys. J. 900, 74 (2020).
Postberg, F. et al. Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus. Nature 459, 1098–1101 (2009).
De Sanctis, M. C. et al. Fresh emplacement of hydrated sodium chloride on Ceres from ascending salty fluids. Nat. Astron. 4, 786–793 (2020).
Kirk, R. L. & Stevenson, D. J. Thermal evolution of a differentiated Ganymede and implications for surface features. Icarus 69, 91–134 (1987).
Kalousová, K. et al. Two-phase convection in Ganymede’s high-pressure ice layer—Implications for its geological evolution. Icarus 299, 133–147 (2018).
Sharp, Z. D. et al. The chlorine isotope composition of chondrites and Earth. Geochim. Cosmochim. Acta 107, 189–204 (2013).
Lellouch, E. et al. Volcanically emitted sodium chloride as a source for Io’s neutral clouds and plasma torus. Nature 421, 45–47 (2003).
Glein, C. R. & Shock, E. L. Sodium chloride as a geophysical probe of a subsurface ocean on Enceladus. Geophys. Res. Lett. 37, L09204 (2010).
Molyneux, P. M. et al. Ganymede’s UV reflectance from Juno-UVS data. Geophys. Res. Lett. 49, e2022GL099532 (2022).
Poch, O. et al. Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids. Science 367, eaaw7462 (2020).
De Sanctis, M. C. et al. Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres. Nature 528, 241–244 (2015).
Waite, J. H. et al. Cassini finds molecular hydrogen in the Enceladus plume: evidence for hydrothermal processes. Science 356, 155–159 (2017).
Mandt, K. E. et al. Protosolar ammonia as the unique source of Titan’s nitrogen. Astrophys. J. Lett. 788, L24 (2014).
Pizzarello, S. & Williams, L. B. Ammonia in the early Solar System: an account from carbonaceous chondrites. Astrophys. J. 749, 161 (2012).
Miller, K. E. et al. Contributions from organic nitrogen to Titan’s N2 atmosphere: new insights from cometary and chondritic data. Astrophys. J. 871, 59 (2019).
Dello Russo, N. et al. Emerging trends and a comet taxonomy based on the volatile chemistry measured in thirty comets with high-resolution infrared spectroscopy between 1997 and 2013. Icarus 278, 301–332 (2016).
Fujiya, W. et al. Migration of D-type asteroids from the outer Solar System inferred from carbonate in meteorites. Nat. Astron. 3, 910–915 (2019).
Melwani Daswani, M. et al. A metamorphic origin for Europa’s ocean. Geophys. Res. Lett. 48, e2021GL094143 (2021).
Gomez Casajus, L. et al. Gravity field of Ganymede after the Juno Extended Mission. Geophys. Res. Lett. 49, e2022GL099475 (2022).
MODTRAN extraterrestrial solar irradiance (National Renewable Energy Laboratory) https://www.nrel.gov/grid/solar-resource/spectra.html#paneld10e138_1
Adriani, A. et al. Juno’s Earth flyby: the Jovian InfraRed Auroral Mapper preliminary results. Astrophys. Space Sci. 361, 272 (2016).
Clark, R. N. & Roush, T. L. Reflectance spectroscopy: quantitative analysis techniques for remote sensing applications. J. Geophys. Res. 89, 6329–6340 (1984).
Heinz D., Chang C.-I. & Althouse, M. Fully constrained least-squares based linear unmixing. In IEEE 1999 International Geoscience and Remote Sensing Symposium (Ed. Stein, T. I.) 1401–1403 (1999); https://doi.org/10.1109/IGARSS.1999.774644
Spade, D. A. in Principles and Methods for Data Science Vol. 43 (eds Srinivasa Rao, A. S. R. and Rao, C. R.) 1–66 (Elsevier North-Holland, 2020).
Acton, C. H. et al. A look towards the future in the handling of space science mission geometry. Planet. Space Sci. 150, 9–12 (2018).
Zimmer, K. et al. SUPCRTBL: a revised and extended thermodynamic dataset and software package of SUPCRT92. Comput. Geosci. 90, 97–111 (2016).
Tosi, F. Data package for the Nature Astronomy paper: ‘Salts and organics on Ganymede’s surface from infrared observations by Juno/JIRAM’ (Tosi et al.). figshare https://doi.org/10.6084/m9.figshare.21710468 (2023).
Ganymede Voyager - Galileo SSI Global Mosaic 1km v1. Annex https://astrogeology.usgs.gov/search/map/Ganymede/Voyager-Galileo/Ganymede_Voyager_GalileoSSI_global_mosaic_1km (2013).
Acknowledgements
The JIRAM instrument is funded by the Italian Space Agency (Agenzia Spaziale Italiana (ASI)). It was built by Selex ES under the leadership of the Italian National Institute for Astrophysics (Istituto Nazionale di Astrofisica (INAF))–Institute for Space Astrophysics and Planetology (Istituto di Astrofisica e Planetologia Spaziali (IAPS)), Rome, Italy. JIRAM is operated by INAF–IAPS, Rome, Italy. F.T., A. Mura, A. Cofano, F.Z., M.C., G.P., C.P., R.S., A.A., A. Migliorini, L.A., F.A., A. Cicchetti, B.M.D., D.G., A. Moirano, M.L.M., R.N., P.S., G.S., S.S. and D.T. acknowledge the support from the ASI–INAF grant no. 2016-23-H.0 plus addendum no. 2016-23-H.2-2021. C.R.G. was supported in part by the NASA grants NNN13D485T and 80NSSC19K0611. Support for S.J.B. and the Juno project is provided under the NASA grant NNM06AA75C to the Southwest Research Institute. J.I.L. acknowledges support from the Juno mission through subcontract D99069MO from the Southwest Research Institute. C.J.H. acknowledges support from the Juno project through a subcontract from the Southwest Research Institute. T.A.N. was supported by the NASA grant 80NM0018F0612. Support from the Juno Science and Operations Teams is gratefully acknowledged.
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Contributions
F.T. led the analysis and interpretation of the JIRAM data, writing major sections of the main text and Methods. A. Mura is the team leader of the JIRAM instrument; he derived geometric information for the JIRAM data, provided correction for stray light and wrote part of the Methods. A. Cofano searched laboratory spectra available in the literature and relevant for the JIRAM spectral range, highlighting the spectral matches in Extended Data Table 1, and performed spectral unmixing. F.Z. mapped the JIRAM data and contributed to the interpretation. C.R.G. wrote a part of the Discussion and Methods sections. M.C. and G.P. contributed to the discussion of results. J.I.L. and C.P. contributed to the data interpretation. R.S. and A. Cicchetti managed the operation of the JIRAM instrument. R.N. was responsible for the JIRAM calibration pipeline. All authors contributed to the discussion of the results and helped with manuscript preparation.
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Extended data
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Supplementary Information
Supplementary Figs. 1–16 and Tables 1–4.
Supplementary Data
TIFF image containing the optical data acquired by the JunoCam camera in its green filter and corresponding to the areas covered by the JIRAM data relating to slit 1.
Supplementary Data
TIFF image containing the optical data acquired by the JunoCam camera in its green filter and corresponding to the areas covered by the JIRAM data relating to slit 2.
Supplementary Data
TIFF image containing the optical data acquired by the JunoCam camera in its green filter and corresponding to the areas covered by the JIRAM data relating to slit 3.
Source data
Source Data Fig. 1b
ASCII file contains the spectral profile shown in Fig. 1b (global average spectrum of Ganymede acquired by JIRAM in sequence PJ34 on 7 June 2021). The first column represents the JIRAM set of wavelengths expressed in micrometres (µm), while the other columns are the I/F value and the associated standard error of the mean (s.e.m.) value, which is also expressed in units of I/F.
Source Data Fig. 2
ASCII file contains the spectral profiles shown in Fig. 2 (average spectral profiles of slits 1–5). The first column represents the JIRAM set of wavelengths expressed in micrometres (µm), while the other columns are the I/F value and the associated standard error of the mean (s.e.m.) value, which is also expressed in units of I/F.
Source Data Fig. 3
ASCII file contains band depth values computed for slits 1–5, as shown in Fig. 3. For each JIRAM pixel/spectrum, geometric information computed with SPICE is also provided.
Source Extended Data Table 1
Complete and fully accessible Excel spreadsheet is presented as Extended Data Table 1. The meanings of the rows and columns in the spreadsheet are specified in the caption.
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Tosi, F., Mura, A., Cofano, A. et al. Salts and organics on Ganymede’s surface observed by the JIRAM spectrometer onboard Juno. Nat Astron 8, 82–93 (2024). https://doi.org/10.1038/s41550-023-02107-5
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DOI: https://doi.org/10.1038/s41550-023-02107-5
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