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Lamy, L., Prange, R., Berthier, J., Tao, C., Kim, T., Roth, L., . . . Melin, H. (2025). A new rotation period and longitude system for Uranus. Nature Astronomy
Open this publication in new window or tab >>A new rotation period and longitude system for Uranus
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2025 (English)In: Nature Astronomy, E-ISSN 2397-3366Article in journal (Refereed) Epub ahead of print
Abstract [en]

The rotation period of Uranus was estimated to be 17.24 +/- 0.01 h in 1986 from radio auroral measurements during the brief Voyager 2 flyby. This value is the basis for the Uranian SIII longitude system still in use. However, the poor period uncertainty limited its validity to a few years, after which the orientation of the magnetic axis was lost. Alternate, conflicting, rotation periods have also been proposed since then. Here we use the long-term tracking of Uranus' magnetic poles between 2011 and 2022 from Hubble Space Telescope images of its ultraviolet aurorae to achieve an updated, independent, extremely precise rotation period of 17.247864 +/- 0.000010 h, only consistent with the Voyager 2 estimate. Its 28-s-longer value and improved accuracy yields a new longitude model now valid over decades, up to the arrival of any future Uranus mission, which will allow the reanalysis of the whole set of Uranus observations. In addition, it has strong direct implications for formation scenarios, interior models, dynamo theories and studies of the magnetosphere. This approach stands as a new method to determine the rotation rate of any object hosting a magnetosphere and a rotationally modulated aurorae, in our Solar System and beyond.

Place, publisher, year, edition, pages
Springer Nature, 2025
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-363563 (URN)10.1038/s41550-025-02492-z (DOI)001461135100001 ()2-s2.0-105002067504 (Scopus ID)
Note

QC 20250519

Available from: 2025-05-19 Created: 2025-05-19 Last updated: 2025-05-20Bibliographically approved
Cartwright, R. J., Hibbitts, C. A., Holler, B. J., Raut, U., Nordheim, T. A., Neveu, M., . . . Villanueva, G. L. (2025). JWST Reveals Spectral Tracers of Recent Surface Modification on Europa. The Planetary Science Journal, 6(5), Article ID 125.
Open this publication in new window or tab >>JWST Reveals Spectral Tracers of Recent Surface Modification on Europa
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2025 (English)In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 6, no 5, article id 125Article in journal (Refereed) Published
Abstract [en]

Europa has been modified by a variety of geologic processes, exposing internally derived materials that are heavily irradiated by charged particles trapped in Jupiter’s magnetosphere. Prior spectral analysis of H 2 O ice on Europa relied on low signal-to-noise data at wavelengths >2.5 μ m, limiting assessment of a 3.1 μ m Fresnel peak that is diagnostic of exposed crystalline ice. We report new measurements of H 2 O ice spectral features using high signal-to-noise data collected by the NIRSpec spectrograph (1.48–5.35 μ m) on the James Webb Space Telescope. These data reveal a narrow 3.1 μ m crystalline H 2 O ice Fresnel peak, which is primarily located at southern latitudes in Tara and Powys Regiones. Our analysis indicates that crystalline ice exposed in these low-latitude regiones is likely sustained by ongoing thermal (re)crystallization outpacing charged particle amorphization of the top ∼10 μ m of Europa’s regolith over short timescales (<15 days). We also measured H 2 O ice features centered near 1.5, 1.65, and 2.0 μ m, and a broad 3.6 μ m H 2 O continuum peak, which are all stronger at northern latitudes, in contrast to the 3.1 μ m Fresnel peak identified at southern latitudes. These results support the hypothesis that H 2 O ice in Europa’s regolith is vertically stratified, with amorphous ice grains dominating its exposed surface, except in Tara and Powys Regiones. We also find that a previously detected 4.38 μ m 13 CO 2 feature is present almost exclusively at southern latitudes in Tara and Powys Regiones, likely derived from an internal source of carbon-bearing material.

Place, publisher, year, edition, pages
American Astronomical Society, 2025
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-364437 (URN)10.3847/PSJ/adcab9 (DOI)001498517700001 ()2-s2.0-105007104379 (Scopus ID)
Note

QC 20250617

Available from: 2025-06-12 Created: 2025-06-12 Last updated: 2025-06-17Bibliographically approved
Masters, A., Roth, L. & Zannoni, M. (2025). Magnetosphere and Plasma Science with the Jupiter Icy Moons Explorer. Space Science Reviews, 221(2), Article ID 24.
Open this publication in new window or tab >>Magnetosphere and Plasma Science with the Jupiter Icy Moons Explorer
2025 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 221, no 2, article id 24Article, review/survey (Refereed) Published
Abstract [en]

The Jupiter Icy Moons Explorer (JUICE) is a European Space Agency mission to explore Jupiter and its three icy Galilean moons: Europa, Ganymede, and Callisto. Numerous JUICE investigations concern the magnetised space environments containing low-density populations of charged particles that surround each of these bodies. In the case of both Jupiter and Ganymede, the magnetic field generated internally produces a surrounding volume of space known as a magnetosphere. All these regions are natural laboratories where we can test and further our understanding of how such systems work, and improved knowledge of the environments around the moons of interest is important for probing sub-surface oceans that may be habitable. Here we review the magnetosphere and plasma science that will be enabled by JUICE from arrival at Jupiter in July 2031. We focus on the specific topics where the mission will push forward the boundaries of our understanding through a combination of the spacecraft trajectory through the system and the measurements that will be made by its suite of scientific instruments. Advances during the initial orbits around Jupiter will include construction of a comprehensive picture of the poorly understood region of Jupiter's magnetosphere where rigid plasma rotation with the planet breaks down, and new perspectives on how Jupiter's magnetosphere interacts with both Europa and Callisto. The later orbits around Ganymede will dramatically improve knowledge of this moon's smaller magnetosphere embedded within the larger magnetosphere of Jupiter. We conclude by outlining the high-level operational strategy that will support this broad science return.

Place, publisher, year, edition, pages
Springer Nature, 2025
Keywords
Jupiter, Ganymede, Europa, Callisto, Magnetospheres, Space plasmas
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-361361 (URN)10.1007/s11214-025-01148-8 (DOI)001436230500001 ()
Note

QC 20250317

Available from: 2025-03-17 Created: 2025-03-17 Last updated: 2025-03-17Bibliographically approved
Roth, L., Blöcker, A., de Kleer, K., Goldstein, D., Lellouch, E., Saur, J., . . . Vorburger, A. (2025). Mass Supply from Io to Jupiter's Magnetosphere. Space Science Reviews, 221(1), Article ID 13.
Open this publication in new window or tab >>Mass Supply from Io to Jupiter's Magnetosphere
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2025 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 221, no 1, article id 13Article, review/survey (Refereed) Published
Abstract [en]

Since the Voyager mission flybys in 1979, we have known the moon Io to be both volcanically active and the main source of plasma in the vast magnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from Io's upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with possible contributions from thermal escape and photochemistry-driven escape. Direct volcanic escape is negligible. The supply of material to maintain the plasma torus has been estimated from various methods at roughly one ton per second. Most of the time the magnetospheric plasma environment of Io is stable on timescales from days to months. Similarly, Io's atmosphere was found to have a stable average density on the dayside, although it exhibits lateral (longitudinal and latitudinal) and temporal (both diurnal and seasonal) variations. There is a potential positive feedback in the Io torus supply: collisions of torus plasma with atmospheric neutrals are probably a significant loss process, which increases with torus density. The stability of the torus environment may be maintained by limiting mechanisms of either torus supply from Io or the loss from the torus by centrifugal interchange in the middle magnetosphere. Various observations suggest that occasionally (roughly 1 to 2 detections per decade) the plasma torus undergoes major transient changes over a period of several weeks, apparently overcoming possible stabilizing mechanisms. Such events (as well as more frequent minor changes) are commonly explained by some kind of change in volcanic activity that triggers a chain of reactions which modify the plasma torus state via a net change in supply of new mass. However, it remains unknown what kind of volcanic event (if any) can trigger events in torus and magnetosphere, whether Io's atmosphere undergoes a general change before or during such events, and what processes could enable such a change in the otherwise stable torus. Alternative explanations, which are not invoking volcanic activity, have not been put forward. We review the current knowledge on Io's volcanic activity, atmosphere, and the magnetospheric neutral and plasma environment and their roles in mass transfer from Io to the plasma torus and magnetosphere. We provide an overview of the recorded events of transient changes in the torus, address several contradictions and inconsistencies, and point out gaps in our current understanding. Lastly, we provide a list of relevant terms and their definitions.

Place, publisher, year, edition, pages
Springer Nature, 2025
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-360067 (URN)10.1007/s11214-025-01137-x (DOI)001413928200001 ()39925795 (PubMedID)2-s2.0-85219121774 (Scopus ID)
Note

QC 20250217

Available from: 2025-02-17 Created: 2025-02-17 Last updated: 2025-03-12Bibliographically approved
Wahlund, J.-E. -., Bylander, L., Giono, G., Ivchenko, N., Kullen, A., Roth, L., . . . Miyoshi, Y. (2025). The Radio & Plasma Wave Investigation (RPWI) for the JUpiter ICy moons Explorer (JUICE). Space Science Reviews, 221(1), Article ID 1.
Open this publication in new window or tab >>The Radio & Plasma Wave Investigation (RPWI) for the JUpiter ICy moons Explorer (JUICE)
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2025 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 221, no 1, article id 1Article, review/survey (Refereed) Published
Abstract [en]

The Radio & Plasma Wave Investigation (RPWI) onboard the ESA JUpiter ICy moons Explorer (JUICE) is described in detail. The RPWI provides an elaborate set of state-of-the-art electromagnetic fields and cold plasma instrumentation, including active sounding with the mutual impedance and Langmuir probe sweep techniques, where several different types of sensors will sample the thermal plasma properties, including electron and ion densities, electron temperature, plasma drift speed, the near DC electric fields, and electric and magnetic signals from various types of phenomena, e.g., radio and plasma waves, electrostatic acceleration structures, induction fields etc. A full wave vector, waveform, polarization, and Poynting flux determination will be achieved. RPWI will enable characterization of the Jovian radio emissions (including goniopolarimetry) up to 45 MHz, has the capability to carry out passive radio sounding of the ionospheric densities of icy moons and employ passive sub-surface radar measurements of the icy crust of these moons. RPWI can also detect micrometeorite impacts, estimate dust charging, monitor the spacecraft potential as well as the integrated EUV flux. The sensors consist of four 10 cm diameter Langmuir probes each mounted on the tip of 3 m long booms, a triaxial search coil magnetometer and a triaxial radio antenna system both mounted on the 10.6 m long MAG boom, each with radiation resistant pre-amplifiers near the sensors. There are three receiver boards, two Digital Processing Units (DPU) and two Low Voltage Power Supply (LVPS) boards in a box within a radiation vault at the centre of the JUICE spacecraft. Together, the integrated RPWI system can carry out an ambitious planetary science investigation in and around the Galilean icy moons and the Jovian space environment. Some of the most important science objectives and instrument capabilities are described here. RPWI focuses, apart from cold plasma studies, on the understanding of how, through electrodynamic and electromagnetic coupling, the momentum and energy transfer occur with the icy Galilean moons, their surfaces and salty conductive sub-surface oceans. The RPWI instrument is planned to be operational during most of the JUICE mission, during the cruise phase, in the Jovian magnetosphere, during the icy moon flybys, and in particular Ganymede orbit, and may deliver data from the near surface during the final crash orbit.

Place, publisher, year, edition, pages
Springer Nature, 2025
Keywords
JUICE, RPWI, Ganymede, Europa, Callisto, Jupiter
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-359182 (URN)10.1007/s11214-024-01110-0 (DOI)001378473600001 ()2-s2.0-105000821961 (Scopus ID)
Note

QC 20250128

Available from: 2025-01-28 Created: 2025-01-28 Last updated: 2025-04-03Bibliographically approved
Sushen, J., Roth, L., Gladstone, R., Ivchenko, N., Pryor, W. & Lamy, L. (2025). Uranus’ hydrogen upper atmosphere: Insights from pre- and post-equinox HST Lyman-α images. Astronomy and Astrophysics, 693, Article ID A231.
Open this publication in new window or tab >>Uranus’ hydrogen upper atmosphere: Insights from pre- and post-equinox HST Lyman-α images
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2025 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 693, article id A231Article in journal (Refereed) Published
Abstract [en]

We present the first spatially resolved images of Lyman-α (Lyα) emissions from Uranus taken by the Hubble Space Telescope (HST). The observations were carried out using HST’s Space Telescope Imaging Spectrograph instrument as part of two far-ultraviolet (FUV) observing campaigns in 1998 and 2011, before and after Uranus’ equinox in 2007. The average intensities (± uncertainties) on Uranus’ disk were 860 ± 6 and 725 ± 9 R, respectively. The images reveal widely extended emissions, detectable up to ~4 Uranus radii (RU). We performed simulations of the Lyα radiative transfer in the atmosphere, considering resonant scattering by H, Rayleigh scattering by H2, and absorption by CH4. We considered only solar Lyα fluxes at Uranus as the Lyα source for simulations. The effects of hydrogen in the interplanetary medium and Earth’s exosphere on Uranus’ Lyα emissions were taken into account. We find a good agreement between on-disk brightnesses from simulations and the HST observations assuming the (H, H2, and CH4) atmosphere profile derived from Voyager 2 measurements. Only slight adjustments of the H or H2 densities were required in some of the simulation cases, in particular, for the 1998 observations. To match the off-disk HST brightnesses in both years, a substantial exosphere of gravitationally bound hot H is required, which we modelled assuming the hot H number density has a Chapman profile. We find that compared to 1998, the hot H abundance required for 2011 is lower and the inferred hot H profiles seem to be more extended. This bound hot H is likely to be a persistent part of Uranus’ upper atmosphere and is distinct from the escaping hot H population derived from Voyager 2 observations. We discuss the possible production mechanisms involving solar EUV radiation and study the sensitivity of the modelled brightness to the parameters of the hot H profile. We find that solar EUV radiation is not a sufficient source to explain the hot H in the exosphere of Uranus.

Place, publisher, year, edition, pages
EDP Sciences, 2025
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-358906 (URN)10.1051/0004-6361/202450719 (DOI)001402042500008 ()2-s2.0-85216427893 (Scopus ID)
Note

QC 20250124

Available from: 2025-01-23 Created: 2025-01-23 Last updated: 2025-02-06Bibliographically approved
Vorburger, A., Fatemi, S., Carberry Mogan, S. R., Galli, A., Liuzzo, L., Poppe, A. R., . . . Wurz, P. (2024). 3D Monte-Carlo simulation of Ganymede's atmosphere. Icarus, 409, Article ID 115847.
Open this publication in new window or tab >>3D Monte-Carlo simulation of Ganymede's atmosphere
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2024 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 409, article id 115847Article in journal (Refereed) Published
Abstract [en]

We present new model results for H2O, O2, H2, O, and H in the atmosphere of Ganymede. The results are obtained from a collision-less 3D Monte-Carlo model that includes sublimation, ion and electron sputtering, and ion and electron radiolysis. Because Ganymede has its own magnetic field, its immediate plasma environment is particularly complex. The interaction between Ganymede's and Jupiter's magnetospheres makes it highly variable in both space and time. The recent Juno Ganymede flyby provided us with new data on the electron local environment. Based on the electron measurements recorded by the Jovian Auroral Distributions Experiment (JADE), we implement two electron populations, one for the moon's polar regions and one for the moon's auroral regions. Comparing the atmospheric contribution of these newly defined electron populations to the overall source and loss processes is one of the main goals of this work. Our analysis shows that for H2O, sublimation remains the most important source process even after accounting for the new electron populations, delivering more than three orders of magnitude more H2O molecules to the atmosphere than all other source processes combined. The source fluxes for O2 and H2, on the other hand, are dominated by radiolysis induced by the auroral electrons, assuming that the electron fluxes JADE measured during Juno's transit of Ganymede's magnetopause current layer are representative of auroral electrons. Atomic O and H are mainly added to the atmosphere through the dissociation of O2 and H2, which is primarily induced by auroral electrons. Our understanding of Ganymede's atmosphere today is mainly based on spectroscopic observations. The interpretation of spectroscopic data strongly depends on assumptions taken, though. Our analysis shows that for a holistic understanding of Ganymede's atmosphere, simultaneous observations of the moon's surface, atmosphere, and full plasma environment (thermal and energetic ions and electrons) at different times and locations (both with respect to Ganymede and with respect to Jupiter) are particularly important. Such measurements are planned by ESA's Jupiter ICy moons Explorer (JUICE), in particular by the Particle Environment Package (PEP), which will greatly advance our understanding of Ganymede and its atmosphere and plasma environment.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Atmosphere, Ganymede, Monte-Carlo model, Sputtering, Sublimation
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-340834 (URN)10.1016/j.icarus.2023.115847 (DOI)001121546700001 ()2-s2.0-85177788162 (Scopus ID)
Note

QC 20231218

Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2024-01-03Bibliographically approved
Bockelée-Morvan, D., Poch, O., Leblanc, F., Zakharov, V., Lellouch, E., Quirico, E., . . . Wong, M. H. (2024). A patchy CO<inf>2</inf> exosphere on Ganymede revealed by the James Webb Space Telescope. Astronomy and Astrophysics, 690, Article ID L11.
Open this publication in new window or tab >>A patchy CO<inf>2</inf> exosphere on Ganymede revealed by the James Webb Space Telescope
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 690, article id L11Article in journal (Refereed) Published
Abstract [en]

Jupiter's icy moon Ganymede has a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only atomic hydrogen and oxygen have been directly detected in this exosphere. Here, we present observations of Ganymede's CO2 exosphere obtained with the James Webb Space Telescope. CO2 gas is observed over different terrain types, mainly over those exposed to intense Jovian plasma irradiation, as well as over some bright or dark terrains. Despite warm surface temperatures, the CO2 abundance over equatorial subsolar regions is low. CO2 vapor has the highest abundance over the north polar cap of the leading hemisphere, reaching a surface pressure of 1 pbar. From modeling we show that the local enhancement observed near 12 h local time in this region can be explained by the presence of cold traps enabling CO2 adsorption. However, whether the release mechanism in this high-latitude region is sputtering or sublimation remains unclear. The north polar cap of the leading hemisphere also has unique surface-ice properties, probably linked to the presence of the large atmospheric CO2 excess over this region. These CO2 molecules might have been initially released in the atmosphere after the radiolysis of CO2 precursors, or from the sputtering of CO2 embedded in the H2O ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO2 precursors. CO2 molecules would then be redistributed via cold trapping on ice-rich terrains of the polar cap and be diurnally released and redeposited on these terrains. Ganymede's CO2 exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
Planets and satellites: atmospheres, Planets and satellites: composition, Planets and satellites: individual: Ganymede
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-355964 (URN)10.1051/0004-6361/202451599 (DOI)001336770600018 ()2-s2.0-85207449206 (Scopus ID)
Note

QC 20241111

Available from: 2024-11-06 Created: 2024-11-06 Last updated: 2024-11-11Bibliographically approved
Tosi, F., Roth, L. & Lorente, R. (2024). Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE. Space Science Reviews, 220(5), Article ID 59.
Open this publication in new window or tab >>Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE
2024 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 220, no 5, article id 59Article, review/survey (Refereed) Published
Abstract [en]

We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): "Surfaces and Near-surface Exospheres of the Satellites, dust and rings".

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
JUICE, Icy Galilean satellites, Geology, Surface composition, Near-surface atmospheres
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-352518 (URN)10.1007/s11214-024-01089-8 (DOI)001286540300001 ()39132056 (PubMedID)2-s2.0-85171888427 (Scopus ID)
Note

QC 20240903

Available from: 2024-09-03 Created: 2024-09-03 Last updated: 2024-09-03Bibliographically approved
Bockelee-Morvan, D., Lellouch, E., Poch, O., Quirico, E., Cazaux, S., de Pater, I., . . . Showalter, M. R. (2024). Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations. Astronomy and Astrophysics, 681, A27, Article ID A27.
Open this publication in new window or tab >>Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 681, p. A27-, article id A27Article in journal (Refereed) Published
Abstract [en]

Context. We present the first spectroscopic observations of Ganymede by the James Webb Space Telescope undertaken in August 2022 as part of the proposal "ERS observations of the Jovian system as a demonstration of JWST's capabilities for Solar System science".Aims. We aimed to investigate the composition and thermal properties of the surface, and to study the relationships of ice and non-water-ice materials and their distribution.Methods. NIRSpec IFU (2.9-5.3 mu m) and MIRI MRS (4.9-28.5 mu m) observations were performed on both the leading and trailing hemispheres of Ganymede, with a spectral resolution of similar to 2700 and a spatial sampling of 0.1 to 0.17 '' (while the Ganymede size was similar to 1.68 ''). We characterized the spectral signatures and their spatial distribution on the surface. The distribution of brightness temperatures was analyzed with standard thermophysical modeling including surface roughness.Results. Reflectance spectra show signatures of water ice, CO2, and H2O2. An absorption feature at 5.9 mu m, with a shoulder at 6.5 mu m, is revealed, and is tentatively assigned to sulfuric acid hydrates. The CO2 4.26-mu m band shows latitudinal and longitudinal variations in depth, shape, and position over the two hemispheres, unveiling different CO2 physical states. In the ice-rich polar regions, which are the most exposed to Jupiter's plasma irradiation, the CO2 band is redshifted with respect to other terrains. In the boreal region of the leading hemisphere, the CO2 band is dominated by a high wavelength component at similar to 4.27 mu m, consistent with CO2 trapped in amorphous water ice. At equatorial latitudes (and especially on dark terrains), the observed band is broader and shifted toward the blue, suggesting CO2 adsorbed on non-icy materials, such as minerals or salts. Maps of the H2O Fresnel peak area correlate with Bond albedo maps and follow the distribution of water ice inferred from H2O absorption bands. Amorphous ice is detected in the ice-rich polar regions, and is especially abundant on the northern polar cap of the leading hemisphere. Leading and trailing polar regions exhibit different H2O, CO2, and H2O2 spectral properties. However, in both hemispheres the north polar cap ice appears to be more processed than the south polar cap. A longitudinal modification of the H2O ice molecular structure and/or nanometer- and micrometer-scale texture, of diurnal or geographic origin, is observed in both hemispheres. Ice frost is tentatively observed on the morning limb of the trailing hemisphere, which possibly formed during the night from the recondensation of water subliming from the warmer subsurface. Reflectance spectra of the dark terrains are compatible with the presence of Na- and Mg-sulfate salts, sulfuric acid hydrates, and possibly phyllosilicates mixed with fine-grained opaque minerals, with a highly porous texture. Latitude and local time variations of the brightness temperatures indicate a rough surface with mean slope angles of 15 degrees-25 degrees and a low thermal inertia Gamma = 20 - 40 J m(-2) s(-0.5) K-1, consistent with a porous surface, with no obvious difference between the leading and trailing sides.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
planets and satellites: composition, planets and satellites: individual: Ganymede, infrared: planetary systems
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-342900 (URN)10.1051/0004-6361/202347326 (DOI)001135685000008 ()2-s2.0-85182020482 (Scopus ID)
Note

QC 20240208

Available from: 2024-02-01 Created: 2024-02-01 Last updated: 2024-02-08Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0554-4691

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