Ganymede’s surface composition from 0.5 to 5.3 µm using combined VLT and JWST datasets and the resulting lessons learned
- 1Institut d’Astrophysique Spatiale, CNRS/Université Paris-Saclay
- 2School of Physics and Astronomy, University of Leicester
- 3LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS
Abstract
Aims . We present a comprehensive spectroscopic investigation of Ganymede’s surface based on the combination of ground-based (MUSE, SPHERE, and SINFONI at the Very Large Telescope) and space-based (NIRSpec on board the James Webb Space Telescope) hyperspectral datasets spanning the visible to the mid-infrared (0.5–5.3 µm).
Methods . After photometric correction using the Oren-Nayar model and cross-calibration of the datasets, we obtained continuous and mutually consistent reflectance spectra over the overlapping regions of the instruments, enabling a detailed analysis of spectral features and surface composition.
Results . The spatial distribution of the absorption bands revealed strong correlations across the datasets and highlighted significant variations in ice grain size and crystallinity, with coarse crystalline ice dominating older grooved terrains and finer grains prevailing in recent crater ejecta and polar regions. These trends reflect the balance between thermal recrystallization and ion-induced amorphization driven by the circum-Jovian plasma. Radiative transfer modeling, using several mixture models (areal, intimate, and multi-scale), shows that Ganymede’s surface is best described by variable mixtures of water ice, polyhydrated magnesium sulfates, sulfuric acid hydrates, and a spectrally neutral darkening agent, which is consistent with previous studies. Older terrains are enriched in sulfates that are likely of endogenous origin, whereas younger plasma-bombarded terrains are dominated by radiolytically produced sulfuric acid hydrates. We further show that intimate and multi-scale mixing models require substantially lower abundances of dark material than previously inferred from linear models, while chlorinated salts remain poorly constrained.
Conclusions . Our results underline the critical need for new laboratory optical constants over extended spectral ranges to fully exploit current and forthcoming observations, particularly in the context of the MAJIS and MISE of the JUICE and Europa Clipper missions.
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BibTeX
@article{royer2026ganymedes,
title = {{Ganymede’s surface composition from 0.5 to 5.3 µm using combined VLT and JWST datasets and the resulting lessons learned}},
author = {C. Royer and F. Poulet and O. King and D. Bockelée-Morvan and N. Ligier and L. N. Fletcher},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202659760},
url = {https://www.aanda.org/10.1051/0004-6361/202659760},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Ganymede’s surface composition from 0.5 to 5.3 µm using combined VLT and JWST datasets and the resulting lessons learned
AU - C. Royer
AU - F. Poulet
AU - O. King
AU - D. Bockelée-Morvan
AU - N. Ligier
AU - L. N. Fletcher
PY - 2026
DA - 2026/10/13
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202659760
UR - https://www.aanda.org/10.1051/0004-6361/202659760
AB - Aims . We present a comprehensive spectroscopic investigation of Ganymede’s surface based on the combination of ground-based (MUSE, SPHERE, and SINFONI at the Very Large Telescope) and space-based (NIRSpec on board the James Webb Space Telescope) hyperspectral datasets spanning the visible to the mid-infrared (0.5–5.3 µm). Methods . After photometric correction using the Oren-Nayar model and cross-calibration of the datasets, we obtained continuous and mutually consistent reflectance spectra over the overlapping regions of the instruments, enabling a detailed analysis of spectral features and surface composition. Results . The spatial distribution of the absorption bands revealed strong correlations across the datasets and highlighted significant variations in ice grain size and crystallinity, with coarse crystalline ice dominating older grooved terrains and finer grains prevailing in recent crater ejecta and polar regions. These trends reflect the balance between thermal recrystallization and ion-induced amorphization driven by the circum-Jovian plasma. Radiative transfer modeling, using several mixture models (areal, intimate, and multi-scale), shows that Ganymede’s surface is best described by variable mixtures of water ice, polyhydrated magnesium sulfates, sulfuric acid hydrates, and a spectrally neutral darkening agent, which is consistent with previous studies. Older terrains are enriched in sulfates that are likely of endogenous origin, whereas younger plasma-bombarded terrains are dominated by radiolytically produced sulfuric acid hydrates. We further show that intimate and multi-scale mixing models require substantially lower abundances of dark material than previously inferred from linear models, while chlorinated salts remain poorly constrained. Conclusions . Our results underline the critical need for new laboratory optical constants over extended spectral ranges to fully exploit current and forthcoming observations, particularly in the context of the MAJIS and MISE of the JUICE and Europa Clipper missions.
SN - 0004-6361
SN - 1432-0746
ER -