We present preliminary results from an ongoing project to assess whether or not the sun shield on JWST may serve as a practical solar calibrator source for ground-based spectroscopic observations of solar system objects. Although this idea may seem wild at first, various aspects of JWST's construction, orbit, and operation conspire to provide an always-visible, high-fidelity solar spectrum at roughly 16th magnitude, which is readily accessible to spectrographs on larger telescopes. We have conducted a multi-epoch observing campaign with SpeX (Rayner et al. 2003) at the NASA Infrared Telescope Facility to obtain low-resolution 0.7-2.5 micron spectra of JWST for direct comparison to contemporary spectra of solar twin calibrator stars (e.g. Ramírez et al. 2014) and main belt asteroids with well characterised reflectance spectra in the SMASS/MITHNEOS catalog (Binzel et al. 2001; Burbine & Binzel 2002). By analysing detections of JWST in survey data from the Asteroid Terrestrial-impact Last Alert System (ATLAS; Tonry et al. 2018), and by imaging it with IO:O at the Liverpool Telescope (Steele et al. 2004; Barnsley et al. 2016), we also place constraints on the variation of its visible brightness. Alongside our up-to-date analysis of JWST’s brightness variation we present a preliminary assessment of our attempts to use its reflectance spectrum to obtain an accurate and useful solar calibration spectrum. Finally, we outline our future plans for this project.

References
Barnsley et al. 2016, JATIS, 2, 015002
Binzel et al. 2001, Icarus, 151, 139
Burbine & Binzel 2002, Icarus, 159, 468
Ramírez et al. 2014, A&A, 572, A48
Rayner et al. 2003, PASP, 115, 362
Steele et al. 2004, Proc. SPIE, 5489, 679
Tonry et al. 2018, PASP, 139, 478

How to cite: Seccull, T. and Siverd, R.: JWST: A Midnight Sun for Planetary Astronomers?, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-278, https://doi.org/10.5194/epsc-dps2025-278, 2025.

JWST observations of TNOs up to 800 km in diameter show surface ices that include carbon-bearing species such as CO₂, CO, CH₃OH, and complex organic molecules (Pinilla-Alonso et al., 2024). Although surface compositions vary, no systematic trend with object size suggests these variations are dominated by surface processes. The surface compositions of larger TNOs display strong methane bands in addition to H₂O ice and CO₂ (Brown, 2012), and recent hydrogen and carbon isotopic measurements of CH₄ on Eris and Makemake by JWST suggest an internal origin for these species (Grundy et al., 2024). The bulk densities of icy moons and dwarf planets support the idea that their refractory cores contain a mixture of CI chondrite and carbonaceous material, reinforcing the idea that carbon-bearing molecules at their surfaces may originate from internal activity. Oxygen fugacity (fO₂) plays a crucial role in controlling the stability of carbonates, graphite, and associated mineral phases, governing carbon speciation and fluid composition in planetary interiors.

We studied the impact of carbon on the mineralogy of trans-Neptunian object (TNO) interiors. We model phase relations in the MgO–SiO₂–Fe–C–H₂ and MgO–SiO₂–CaO–Fe–C–H₂ systems across the P–T range of TNOs (300–1300 K, 1–7000 bar), using thermodynamic modeling with Perple_X (Connolly, 2005) and assuming CI elemental composition. The results reveal that at high fO₂, carbonates (magnesite, dolomite), water, and CO₂ are stable, whereas at lower fO₂, carbon is progressively reduced to graphite, with methane and hydrogen as the dominant volatiles. The stability fields of major species (CO₂, H₂O, CH₄) in COH fluids are bounded by different oxygen fugacity buffers defined by the stability of various carbon-bearing mineral assemblages. Conversely, if fluid composition is fixed, for example by degradation reactions of carbonaceous matter, it will determine the mineral assemblages. Pressure does not significantly influence these transitions, whereas changes in oxygen fugacity and temperature strongly affect the gas species released from the mineral assemblage into metamorphic fluids. Specifically, at high temperatures, reduced phases such as methane are stable, while at lower temperatures, oxidized species and CO₂ are favored. Thus, temperature and oxygen fugacity play a crucial role in controlling the nature of carbon-bearing phases in solids and in fluids that can reach the surface of TNOs.

The predicted metamorphic evolution of mineral assemblages shows that the internal composition is directly reflected in fluid composition, which may eventually reach the surface and atmosphere of TNOs. Small TNOs (typically <800 km in diameter) have cold cores and therefore high oxygen fugacity, supporting the idea of oxidized interiors where carbonates and CO₂ are stable. In contrast, large TNOs such as Eris, Makemake, and Pluto, with higher core temperatures and/or lower oxygen fugacity, likely host more reducing phases, leading to the release of reduced fluid species such as methane. Overall, these findings suggest that redox-driven transformations have significantly shaped the interiors and volatile emissions of icy, carbon-rich bodies in the outer solar system, influencing their potential habitability. These results are consistent with JWST and earlier spectroscopic observations suggesting that volatiles of internal origin contribute to present-day surface compositions. It is predicted that CH₄ should become increasingly dominant as TNO size increases, a hypothesis that will be tested further by upcoming JWST spectroscopic investigations of TNOs.

Acknowledgement

This work was supported by Institut National des Sciences de l'Univers through Programme National de Planétologie, by the Agence Nationale de la Recherche (ANR, project OSSO BUCO, ANR-23-CE49-0003) and by the European Union (ERC, PROMISES, project #101054470). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.

References:

Brown, M. E. (2012). The Compositions of Kuiper Belt Objects. Annual Review of Earth and Planetary Sciences, 40 (Volume 40, 2012), 467–494. https://doi.org/https://doi.org/10.1146/annurev-earth-042711-105352

Connolly, J. A. D. (2005). Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation. Earth and Planetary Science Letters, 236(1–2), 524–541. https://doi.org/10.1016/j.epsl.2005.04.033

Grundy, W. M., Wong, I., Glein, C. R., Protopapa, S., Holler, B. J., Cook, J. C., Stansberry, J. A., Lunine, J. I., Parker, A. H., Hammel, H. B., Milam, S. N., Brunetto, R., Pinilla-Alonso, N., de Souza Feliciano, A. C., Emery, J. P., & Licandro, J. (2024). Measurement of D/H and 13C/12C ratios in methane ice on Eris and Makemake: Evidence for internal activity. Icarus, 411. https://doi.org/10.1016/j.icarus.2023.115923

Pinilla-Alonso, N., Brunetto, R., De Prá, M. N., Holler, B. J., Hénault, E., Feliciano, A. C. de S., Lorenzi, V., Pendleton, Y. J., Cruikshank, D. P., Müller, T. G., Stansberry, J. A., Emery, J. P., Schambeau, C. A., Licandro, J., Harvison, B., McClure, L., Guilbert-Lepoutre, A., Peixinho, N., Bannister, M. T., & Wong, I. (2024). A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects. Nature Astronomy. https://doi.org/10.1038/s41550-024-02433-2

How to cite: Confortini, G., Delarue, C., Reynard, B., and Sotin, C.: Thermodynamic modeling of metamorphic fluids supports internal source of carbon-bearing molecules at the surface of TNOs, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-622, https://doi.org/10.5194/epsc-dps2025-622, 2025.

JWST’s infrared exploration of the Saturn system has been designed to extend the legacy of the Cassini-Huygens mission, using the exquisite sensitivity, spectral coverage, and spectral resolution of the integral field units (IFUs) to reveal new insights into the atmosphere, ionosphere, rings and moons.  Guaranteed-time programme GTO1247 used MIRI/MRS (4.9-28.5 µm) to explore Saturn’s seasonal circulation patterns during northern summer [1], and a combination of NIRSpec/IFU (1.8-5.3 µm) and MIRI/MRS to diagnose the icy composition of Saturn’s rings and small moons [2].  GTO1251 explored Titan’s atmosphere[3], GTO1250 revealed the extent of Enceladus’ watery plumes [4], while guest-observer programme GO3716 explored Saturn’s irregular satellites [5]. 

NIRCam Imaging (June 2023):  NIRCam observations of Saturn at 3.23 µm (GTO1247) reveal structures never-before-seen in Saturn’s upper atmosphere (Fig. 1). Observations in this strong methane absorption band, overlain by methane fluorescence, show diffuse patterns across the disc, with dark polar domains in the north and south in Fig. 2, a faint auroral oval in the north, and unexpected structure (patches of brightness and darkness) extending from the poles towards mid-latitudes suggesting high-altitude wave activity.  Conversely, images at 2.12 µm reveal bright reflection from polar hazes, with the northern hexagon (78^oN) and ribbon wave (48^oN) clearly visible, and small cyclones and anticyclones observed in both hemispheres.  Brightness gradients at 2.12 µm reveal the edges of Saturn’s bands (Fig. 2), coinciding with zonal jets measured by Cassini.  Intriguingly, zonally-averaged gradients at 3.23 µm also show peaks at the jet locations, suggesting that the winds provide zonal organisation to the 3.23 µm structure and that both stratospheric aerosols (sculpted by zonal winds) and CH₄ fluorescence (likely independent of the winds) are contributing to the unusual appearance at 3.23 µm.

Figure 1 NIRCam images of Saturn at 3.23 µm (left, with rings saturated to show atmospheric detail) and 2.12 µm (right), acquired in GTO1247 in June 2023.

Figure 2 Polar projections of NIRCam data at 3.23 µm (top row) and 2.12 µm (bottom row), for northern and southern hemispheres.  The auroral oval is evident at 3.23 µm (top left); and small vortices, the hexagon and ribbon can be seen at 2.12 µm (bottom left).  Zonally-averaged brightnesses (and their poleward gradients) are shown on the right, compared to the locations of Saturn’s prograde jet peaks (vertical dashed lines).

NIRSpec Spectroscopy (November 2024):  Missing from the JWST Saturn observations of Cycles 1 and 2 was NIRSpec/IFU spectroscopy, without which it would be challenging to distinguish ionospheric emissions from H₃⁺ or CH₄ fluorescence from reflection from stratospheric hazes.  In Cycle 3, GO 5308 [6] acquired a full NIRSpec/IFU map of Saturn’s northern hemisphere poleward of 45^oN, spanning 2.8-5.3 µm using the F290LP/G395H filter/grating.  Saturn was observed continuously between 04:00-13:58 UT on 29 November 2024 to observe all longitudes, resulting in 26 spectral cubes each constructed from four dithers.  Cubes were processed using a custom pipeline to reduce saturation and assign geometry [7], producing polar projections (Fig. 3) and zonally-averaged spectra (Fig. 4).

Results:  Combining the 2023 NIRCam observations with the 2024 NIRSpec observations, we observe the following:

• Extratropical and Polar Belt/Zone structure: Zonal jets organise both reflectivity and thermal emission, even in the CH₄ fluorescence band near 3.32 µm (sounding high altitude). Latitudinal banding at 5-µm is on a scale finer than the zonal jets, potentially due to different latitudinal distributions of at least two aerosol layers: an upper tropospheric haze p < 0.3 bars, and a deeper cloud layer at 1–2 bars.  Latitudinal gradients in aerosol opacity, phosphine, ammonia, and water, will be compared to the jet locations to search for evidence of vertical mixing on the scale of Saturn’s belts and zones. 
• Polar Domain and Hexagon: As previously reported by MIRI/MRS in 2022 [1], NIRSpec shows that the north pole remains dark at 5 µm and surrounded by a cloud-free band of bright emission, consistent with its appearance in Cassini/VIMS observations in 2016 [8].  This latitudinal contrast prevents us from seeing Saturn’s hexagon (78^oN) in thermal emission, but reflected sunlight near 2-3 µm clearly reveals the six vertices of the hexagon with a westward translation between 2023 and 2024.  These data are possibly our last view of the hexagon before it becomes hidden in autumn darkness after Saturn’s equinox (May 2025), and confirm that the hexagon has now existed for at least ~45 years (since discovery by Voyager).
• Discrete Atmospheric Features: NIRCam (Fig. 2) reveals the presence of a long-lived cyclone-anticyclone pair (one dark, one bright) near 60-65^oN that were also evident in Hubble observations in 2022-23.  The NIRSpec data at 3 µm (Fig. 3) reveal the same vortex pair near 60^oN, 135^oW in 2024.  In the southern hemisphere, NIRCam reveals reflective ovals near 44^oS and 55^oS that also appear to have persisted for several years (observed by Hubble as the south emerged from winter darkness).
• Large-Scale Upper Atmospheric Structure: Both NIRCam and NIRSpec reveal significant longitudinal structure in the 3.2-3.3 µm range sensitive to high-altitude aerosols and CH₄ fluorescence (Fig. 3-4). NIRSpec reveals at least four dark patches extending equatorward of the dark north polar domain, creating a wave-like appearance at mid-latitudes that has changed between 2023 and 2024.  NIRCam reveals hints of similar structure around the South Pole.  We will present spectral retrieval analyses to determine the likely origin (CH₄ fluorescence, stratospheric hazes) for these unexpected structures.

Figure 3 Polar projections of NIRSpec data in November 2024, showing brightness (top row) and residual from the zonal mean (bottom row) at 5.1 µm (showing deep thermal emission), 3.0 µm (showing aerosol reflection), and 3.32 µm (a blend of CH₄ fluorescence and aerosol reflection).

Figure 4 Zonally-averaged NIRSpec spectra at 55 and 75^oN, with key gaseous absorptions (and fluorescent emission) labelled.

References

• Fletcher et al., 2023, DOI: 10.1029/2023je007924.
• Hedman et al., 2024, DOI: 10.1029/2023je008236.
• Nixon et al., Nature Astronomy, 2025.
• Villanueva et al., 2023, DOI: 10.1038/s41550-023-02009-6.
• Belyakov and Brown, 2025, DOI: 10.48550/arXiv.2503.20046.
• Moore et al., Hunting for the source of Saturn's atmospherically driven aurora. 2024. 5308.
• King et al., 2023, DOI: 10.3847/2515-5172/ad045f.
• Sromovsky et al., 2021, DOI: 10.1016/j.icarus.2021.114409.

How to cite: Fletcher, L. N., Moore, L., Stallard, T. S., Melin, H., Toogood, S., King, O. R. T., Roman, M. T., Harkett, J., Hammel, H. B., Tiscareno, M., Milam, S., and Showalter, M.: JWST NIRCam and NIRSpec Mapping of Bands, Waves, and Vortices in Saturn's Mid-Latitudes and Polar Domains, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-651, https://doi.org/10.5194/epsc-dps2025-651, 2025.

Asteroid (3200) Phaethon is a unique near-Earth asteroid with a perihelion of 0.14 AU. It experiences extreme temperatures exceeding 1000 °C during its close solar approaches. The asteroid follows a highly eccentric orbit (e ~ 0.89) and is notable as the parent body of the Geminid meteor shower (a rare case where its origins come from an asteroid rather than a comet [1]). Observations from the Solar Terrestrial Relations Observatory (STEREO) have shown sodium emissions from Phaethon at perihelion [2]. These emissions suggest that the asteroid’s surface undergoes active and potentially transformative processes under intense solar heating. Spectroscopic data from the NASA Infrared Telescope Facility (IRTF) and the James Webb Space Telescope (JWST) show no detectable 3-µm absorption feature, indicating that Phaethon’s surface is dehydrated [3][4]. Additionally, JWST GTO Program 1245 observed Phaethon with the Mid-Infrared Instrument (MIRI), providing insights into compositional properties in this wavelength region. This presentation will discuss in-depth research on Phaethon’s thermal history and surface evolution.

To model Spitzer IRS observations of (3200) Phaethon, Maclennan & Granvik (2024)[5] looked for meteorite analogs and corresponding minerals for the asteroid from the RELAB database[6]. Their work’s analysis suggests that CY carbonaceous chondrites are good meteorite analogs, with olivine samples of varying forsterite percentages as good mineral analogs. Starting materials for their linear mixing model were selected to represent primitive, aqueously altered compositions (carbonaceous chondrites) and minerals that are products of Phaethon’s thermal evolution (secondary olivine, enstatite). We build on this study with our higher resolution and signal-to-noise JWST MIRI data [4], starting with similar carbonaceous chondrites and olivine samples in our analysis.

The meteorite analog and olivine (fo40 to fo80) mid-infrared data from RELAB were compared to the collected asteroid spectrum to begin constraining the mineralogical signatures observed in the JWST MIRI data. Both qualitative and quantitative spectral matching techniques were applied, and the results indicate that CY carbonaceous chondrite Y-86720 [4] appears to be the best match to Phaethon’s mid-infrared spectrum (Fig. 1). In addition, fo68 was the best-fit match to the olivine present on the surface, which differs from the previously best-fit forsterite percentage found in the previously published work [5]. This is likely due to the SNR of our data allowing for viewing of specific features like those in the 17 micron region.

With these constraints, we used a linear mixing model to combine mineral spectra and compare to the MIRI spectrum. We use mineral spectra from the RELAB database, including minerals relevant to olivine hydration and thermal alteration pathways. Troilite (FeS) was included in the mixing model to account for potential sulfide phases, though its use was minimized in the fits as troilite is expected to become unstable and devolatilize at the temperatures that Phaethon reaches near perihelion [7]. A mean absolute error (MAE) calculation was performed across the wavelength range, providing a quantitative assessment of how effectively the model reproduced the mid-infrared spectra. This modeling approach was compared to previous efforts [5] that utilized the Spitzer spectrum. A diagnostic feature at 17.5 µm, corresponding to the Christensen feature associated with phyllosilicate vibrations, is notably flat in the JWST MIRI data. This behavior suggests a high degree of dehydration, as this diagnostic feature disappears with thermal alteration of the phyllosilicates. The updated JWST-based modeling (Fig. 2) provides a more refined view of Phaethon’s surface composition, indicating dehydration and thermal processing from experiencing the high temperatures with close passes to the Sun that was not fully captured by the Spitzer observations. The model analysis suggests that Phaethon’s surface likely includes enstatite and secondary olivine that would have formed alongside the enstatite during thermal processing.

We are also interested in how solar heating alters the asteroid’s surface and subsurface, as remote observations only give us surface-level data. To explore this, we employed a thermal conduction model (KRC) to simulate the diurnal and annual heating cycles. This allowed for examination of how deeply high temperatures penetrated into the asteroid’s subsurface. The takeaway from this work is that primitive and aqueously altered rock is likely not found too deep under the surface because such materials are less affected by the intense heat of perihelion. Our thermal models show a dropoff of temperature as two or three skin depths are passed.

We will present our in-depth research into Phaethon’s mid-infrared spectrum, linear mixing model, and thermal model. Our work, which uses new JWST data and expands on previous studies, will yield a better understanding of the composition of Phaethon and its thermal history. 

References:
[1] https://blogs.nasa.gov/parkersolarprobe/2023/06/14/scientists-shed-light-on-the-unusual-origin-of-a-familiar-meteor-shower/

[2] Qicheng Zhang et al 2023 Planet. Sci. J. 4 70

[3] Takir, D., Kareta, T., Emery, J.P. et al. Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration. Nat Commun 11, 2050 (2020). https://doi.org/10.1038/s41467-020-15637-7

[4] https://doi.org/10.48550/arXiv.2505.00692

[5] MacLennan, E., Granvik, M. Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon. Nat Astron 8, 60–68 (2024). https://doi.org/10.1038/s41550-023-02091-w

[6] This research utilizes spectra acquired from Ralph E. Milliken, Tim Glotch, Don Lindsay, and others with the NASA RELAB facility at Brown University

[7] https://www.hou.usra.edu/meetings/metsoc2024/pdf/6409.pdf

How to cite: Madden-Watson, A. O., Thomas, C. A., Haberle, C. W., Rivkin, A. S., Hammel, H. B., and Milam, S. N.: A Scorched Story: JWST Reveals Phaethon's Dehydrated Surface Composition and Thermal History, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-805, https://doi.org/10.5194/epsc-dps2025-805, 2025.

We present observations of Jupiter’s south polar region using the JWST/NIRSpec IFU spectrometer, providing high resolution spectral imaging across the near-infrared that probes the vertical and latitudinal distribution of aerosols and gaseous species.  Near-infrared spectroscopic mapping is a powerful diagnostic for studying giant planet atmospheres, enabling constraints on cloud structure in the weather-forming lower troposphere, and haze in the radiatively-controlled lower stratosphere.  The 1.7-5.3 µm range sampled here provides access to reflected sunlight both inside and outside of strong methane absorption bands; ionospheric emission from CH₄ and H₃⁺; and deep thermal emission from the 5 µm window where gaseous absorption is relatively low; sensing the 1 – 10 bar region. Locating and constraining the aerosol layers of Jupiter’s atmosphere is of great importance for photochemical models, as these hazes are produced in high-altitude photochemistry [1], and affect the efficiency of radiative heating and cooling of the upper troposphere and stratosphere [2]. The highest latitudinal zonal jets entrain a cold polar vortex, with clear transitions in aerosol properties (and potentially gaseous abundances) across the polar vortex boundary. Reflective aerosols may also be created by auroral particle precipitation [3] which allows magnetospheric phenomena to be traced onto the Jovian clouds [4]. We will invert the JWST NIRSpec observations to explore how aerosol and gaseous properties differ between the south polar vortex and the mid-latitudes.

JWST/NIRSpec observed the south pole of Jupiter on 24 December 2022 as part of ERS-1373 (Co-PIs: de Pater & Fouchet), using the high-resolution, long-wavelength filter/grating combination F290LP/G395H (2.8 – 5.3 µm). This provides exceptional spectral resolution (R~2700, =0.7nm) over the latitude range 42 – 85^oS at spatial resolutions between 74km at 42^oS and 1100km at 85^oS. Six tiles were taken using this grating, giving 100^o of longitudinal coverage, and three tiles were taken with F170LP/G235H (1.7 – 3.2 µm) extending the wavelength range down to 1.7µm. This covers the full near-IR range, from short-wavelength reflected sunlight to long-wavelength thermal emission. Hubble and Juno also observed the region at a similar time (2022/11/12 and 2022/12/15) allowing comparison of features in visible light and tracking over time in the same wavelength range.

The vertical structure of aerosols and gases will be determined using spectral modelling and inversion package NEMESIS [5]. A key challenge is modelling and removing the ionospheric emissions from methane fluorescence and H₃⁺, which is done outside NEMESIS, before performing the multiple-scattering retrievals to constrain aerosol properties. We vary the vertical profile of several gases including PH₃ and NH₃ and compare hazes in the upper troposphere and stratosphere atop a single extended cloud deck in the troposphere. We found that a stratospheric haze is required to replicate the broad shape of the region between 3.2 µm and 3.6 µm, where an upper tropospheric haze alone is not sufficiently reflective. Once these gas profiles and aerosols are tuned to provide a physical best-fit, model will be applied to zonally-averaged spectra across the full latitude range of the observations in order to study the changes in chemistry and aerosol properties that occur over the polar vortex boundary.

Figures:

Figure 1 The South Polar region observed by JWST/NIRSpec using G395H at 4 selected wavelengths. Top: Mosaic in the RA/Dec frame, rotated such that North is up. Bottom: reprojected onto an equidistant polar projection. 2.93µm (a) shows sunlight reflecting off the main cloud deck, 3.513µm (b) shows the highly reflective stratospheric haze layer, 3.953µm (c) is dominated by auroral emission from excited H₃⁺ ions, and 4.7µm (d) shows thermal emission from deep within Jupiter (1 – 10bar). Context images are Hubble OPAL visible light images from Nov 2022.

Figure 2 Top: Observed radiance with JWST as a function of latitude and wavelength. Bottom: Two zonally averaged spectra at 50^oS and 80^oS, with some gas absorption/emission features labelled. The difference between the mid-latitude and high-latitude spectra are evident, with broadband methane and phosphine absorption disappearing at high latitude, and auroral emission from H3+ and CH4 becoming more dominant.

References:

[1]  Wong, A.-S., Y. L. Yung, and A. J. Friedson (2003), Benzene and Haze Formation in the Polar Atmosphere of Jupiter, Geophys. Res. Lett.

[2] Zhang X., West R. A., Banfield D., and Y.L. Yung (2013), Stratospheric aerosols on Jupiter from Cassini observations, Icarus

[3]: Sinclair J.A., Moses J.I., Hue V., Greathouse T.K., Orton G.S., Fletcher L.N., Irwin P.J.G (2019), Jupiter's auroral-related stratospheric heating and chemistry III: Abundances of C2H4, CH3C2H, C4H2 and C6H6 from Voyager-IRIS and Cassini-CIRS, Icarus

[4]: Tsubota, T.K., Wong, M.H., Stallard, T., Zhang X., Simon, A. (2025), UV-dark polar ovals on Jupiter as tracers of magnetosphere–atmosphere connections, Nature Astronomy

[5]: Irwin P.G.J., Teanby N.A., de Kok R., Fletcher L.N., Howett C.J.A., Tsang C.C.C., Wilson C.F., Calcutt S.B., Nixon C.A., Parrish P.D. (2008), The NEMESIS planetary atmosphere radiative transfer and retrieval tool, Journal of Quantitative Spectroscopy and Radiative Transfer

How to cite: Toogood, S., Fletcher, L., King, O., Harkett, J., Roman, M., de Pater, I., Biagiotti, F., Melin, H., Fouchet, T., Wong, M., and Rodriguez-Ovalle, P.: JWST/NIRSpec IFU Observations of Jupiter’s South Pole: Vertical and Latitudinal Structure of Aerosols in the Near-Infrared, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-820, https://doi.org/10.5194/epsc-dps2025-820, 2025.

The new Polana collisional family is the hypothesized origin of the near-Earth asteroids (101955) Bennu, which was the target of the NASA OSIRIS-REx mission, and (162173) Ryugu, which was the target of the JAXA Hayabusa2 mission. We present JWST NIRSpec and MIRI spectroscopy of the parent body of the family, (142) Polana, and compare it with spacecraft and laboratory data of both near-Earth asteroids. We find that the near-infrared spectrum of Polana is similar to that of the returned sample from both Bennu and Ryugu, but has a slope that differs from that of the global average spectra taken by both spacecraft. The mid-infrared Polana spectrum differs in shape from the global average spectrum of Bennu, possibly because of porosity, space weathering, or grain size. Spectral features at similar wavelengths in the spectra of Polana and Bennu and Ryugu support the hypothesis that both asteroids originated in the Polana family. 

How to cite: Arredondo, A., Becker, T., McAdam, M., Rivkin, A., Jarmak, S., and Wong, I.: JWST spectroscopy of the parent body of the new Polana collisional family , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-938, https://doi.org/10.5194/epsc-dps2025-938, 2025.

In 2024, we published numerical simulations of Jovian anticyclones, including the Great Red Spot (GRS), that are solutions to the governing three-dimensional, compressible equations of motion. Our calculations depended on several unknown parameter values of the atmosphere that cannot be directly observed (e.g., the heights of the top of the convective zone, the heights of the top, middle,  and bottom of the GRS, and the temperatures of the atmosphere at heights from the convective zone up to 700mb). A wide range of parameter values produced stable vortices with velocities that matched the HST observations, including its hollowness (i.e., its quiet, and sometimes cyclonic center). However, it took a detailed search of the unknown parameter space to find the (apparently) one set of parameter values that produces an anticyclone that fits the GRS’s HST velocities and the JWST thermal observations of its anomalously cold top near 400mb. While exploring parameter space, we found that minor changes of the temperature profile and other parameters made large and qualitative changes to the vortex (e.g., changing it from hollow to unhollow, altering its vertical thickness, and/or adjusting its height in the atmosphere, vortical intensity and/or horizontal area, or making it unstable). Knowledge of how the vortices changed with respect to their parameter values not only provides us with an understanding of how hollowness occurs in vortices but also gives us guidance on the parameter values that are needed to simulate other Jovian vortices, especially the Red Oval, which we shall soon observe with the JWST and map its winds. The sensitivity of the GRS to subtle changes of the  parameter values provides us with a starting point as to understanding how subtle changes in the parameter values of the Jovian atmosphere might have caused the GRS to change since its Voyager observations - particularly, its shrinkage and its increase in its vertical vorticity.

Caption. The anomalous vertical vorticity of the GRS from our published simulation in the Journal of Fluid Mechanics 984 (2024): A61. https://doi.org/10.1017/jfm.2024.132.  The anticlonic vorticity is in red, and the cyclonic vorticity is blue. Left Panel shows the GRS in the vertical-north/south plane.  The origin of the vertical coordinate is aribtrary. The three dashed lines are the heights of the HST clouds  (purple), JWST clouds (green) , and the top of the convective zone (blue). The hollowness is only in the upper part of the GRS. The largest vorticities are below the visible clouds and have Rossy numbers of unity or greater, making the GRS ageostrophic. We find, in general, that the bottoms of our simulated vortices are unable to penetrate into the convective zone, and the GRS has no penetration. Note that the panel is stretched in the vertical direction and that the GRS is just greater than two hundred kilometers thick, while it is more than ten thousands kilometers wide. Right Panels: Top Panel shows the GRS in the east/west-north/south plane at 1.2 bar, approximately the height of the HST clouds, and the Bottom Panel shows the GRS in the same plane at 400mbar, approximately the height of the JWST clouds .

How to cite: Marcus, P., Kim, S., Wong, M., de Pater, I., and Simon, A.: 3D Solutions to the Equations of Motion of Jovian Vortices constrained by JWST Temperatures and Velocities Along with HST Velocities , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-416, https://doi.org/10.5194/epsc-dps2025-416, 2025.

Saturn’s largest moon Titan has a nitrogen-methane atmosphere and a rich organic photochemistry. Dissociation of Titan’s molecular methane and nitrogen into N and methyl (CH₃) radicals forms the basis of this photochemistry and results in a vast array of hydrocarbon and nitrile species. The abundance of CH₃ is thus of critical importance to understanding Titan’s atmospheric chemistry. CH₃ is predicted by photochemical models and must be present to explain Titan’s trace gas composition, but has never been directly observed. Cassini’s mass spectrometer was unable to make a detection as the extreme reactivity of radicals results in reactions on the instrument wall (e.g. recombination with H) before detection is possible. Emission features in the infra-red are also very weak, so detection from remote-sensing spectroscopy has previously not been possible. Here we use the very high sensitivity of the James Webb Space Telescope’s (JWST) Mid-InfraRed Instrument (MIRI) to detect emission from CH₃ at 16.5 microns. We have used this to validate model predictions that underpin Titan’s rich atmospheric chemistry.

JWST/MIRI observations were taken in Medium Resolution Spectroscopy (MRS) mode on 11^th July 2023 as part of Guaranteed Time Observation programme 1251 [Nixon et al., 2025]. Observations were reduced using the standard pipeline and combined to give a disc-averaged spectrum (Fig 1). The observed spectrum was compared to a forward model generated with a reference Titan atmosphere using the NEMESIS radiative transfer suite [Irwin et al., 2008]. The reference atmospheric temperature profile was based on observation from Cassini half a Titan year previous, augmented with ground-based measurements from ALMA and in-situ measurements from the Huygens probe (Fig 2a). A baseline atmospheric composition was compiled from Cassini/Huygens measurements [Teanby et al., 2019]. For the CH₃ profile, in the absence of measurements, we used the predicted abundance from a photochemical model [Vuitton et al., 2019] (Fig 2a).

The abundance profile of CH₃ is expected to be extremely steep with very high fractional abundances in the thermosphere (100 ppm at 1000km) and much lower abundances in the stratosphere and mesosphere (1 ppb at 300km). Peak emission under conditions of local thermodynamic equilibrium should originate from the mid-thermosphere at an altitude of ~800km (Fig 2b). However, our analysis shows that non-local thermodynamic equilibrium (non-LTE) emission is expected due to very low thermospheric pressures [Nixon et al., 2025]. This supresses emission below that expected from the Planck function and reduces infra-red emission from thermospheric CH₃ to negligible levels. When non-LTE effects are considered, we find that the emission instead originates from the stratopause region (~300km) where CH₃ abundances are predicted to be around 1 ppb (Fig 2c).

Agreement between forward modelled non-LTE emission using the photochemical model profile and the JWST/MIRI observation match very well (Fig 1) – confirming the model predicted abundances are consistent with conditions in Titan’s middle atmosphere. Our initial results were presented in Nixon et al., (2025). Here we present an updated analysis using improved pipeline processing, more in-depth treatment of the disc-averaged nature of the observation, and provide formal limits on the CH₃ abundance profiles. The consistency of our results with predictions from photochemical models gives confidence to current chemical schemes for Titan’s low-order chemistry, which provides a sound basis for a deeper analysis of Titan’s more exotic species such as high-order hydrocarbons and poly-aromatic hydrocarbons.

References

Irwin, P.G.J., et al., 2008. The NEMESIS planetary atmosphere radiative transfer and retrieval tool. Journal of Quantitative Spectroscopy and Radiative Transfer 109, 1136–1150.

Nixon, C.A., et al., 2025., Titan’s Atmosphere in Late Northern Summer from JWST and Keck Observations. Nature Astronomy, in press.

Teanby, N.A., et al., 2019. Seasonal Evolution of Titan’s Stratosphere During the Cassini Mission. Geophysical Research Letters 46, 3079–3089.

Vuitton, V., et al., 2019. Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model. Icarus 324, 120–197.

Fig 1: JWST/MIRI disc-average spectrum compared with forward models with and without CH₃. The model including CH₃ provides a much better fit to the observations.

Fig 2: (a) Titan’s atmospheric temperature structure and uncertainty envelope from Nixon et al. (2025), along with photochemical model prediction of the CH₃ profile from Vuitton et al. (2019). (b) Contribution functions for LTE case with nominal temperature profile (green), hot temperature limit (red) and cold temperature limit (blue). For LTE, peak emission would be from the thermosphere at ~800km, but this is not realistic. (c) Contribution functions for a more realistic non-LTE emission case peak at ~300km around the mesopause as non-LTE effects suppress emission at very low pressures. Our observations are thus most sensitive to abundances around the stratopause.

How to cite: Teanby, N., Nixon, C., López-Puertas, M., Coy, B., Vuitton, V., Lavvas, P., Wright, L., Ford, J., and Irwin, P.: Methyl Radical Detected on Titan with JWST/MIRI, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-117, https://doi.org/10.5194/epsc-dps2025-117, 2025.

The James Webb Space Telescope (JWST) offers, for the first time, routine mid-infrared imaging capable of detecting the thermal glow of kilometre- and sub-kilometre-scale asteroids that are invisible to ground-based optical surveys. We present the first systematic data-mining campaign targeting publicly released MIRI images acquired between March 2022 and October 2023. We analyzed data from 29 programmes that targeted pointings that fell within ±10° of the ecliptic, and grouped them into 171 fields that could be searched for moving objects, spanning a cumulative area of about 0.1 deg². A GPU-accelerated linear-motion pipeline, tuned to JWST’s dither strategy and resolution, recovered 17 moving sources consistent with main-belt orbits, 14 of which have no prior catalogue entry. Most objects were detected in several MIRI filters, spanning F770W–F2100W.

We considered a model spectrum using the Planetary Spectrum Generator (PSG) for a canonical asteroid at 2.9AU and pV=0.13, to obtain typical colors of an asteroid, and the expected visible magnitudes in the range g′ ≈ 24–29, and diameters of ~0.3–5 km assuming moderate albedos. When comparing with multi-filter photometry we obtain a systematically bluer F770W–F1500W slopes than those predicted for the comparison asteroid.

We estimate our detection efficiency by injecting synthetic PSFs, and recovering them in each field and filter in our dataset. These translated to visible g’ magnitudes, and combined with the surveyed area, and asteroid luminosity function predict an expected yield of 27_{-5}^{+70} serendipitous asteroids, only ∼2 σ above our observed yield. The faint-end turnover we detect is therefore genuine and, if confirmed, will tighten constraints on collisional models and the size–frequency distribution below D ≈ 1 km. Extrapolating our cadence to the ∼2 deg² of MIRI and NIRCam imaging already in the archive suggests JWST is on course to deliver ≥100 main-belt discoveries by Cycle 5 and >500 over a ten-year mission, probing down to D ≃ 0.2 km at 2–3 AU and to D ≃ 1 km in the outer belt.

Our pilot survey demonstrates that the JWST archive harbours a rich and largely untapped reservoir of small bodies. By exploiting this resource we will construct an infrared census of the main belt and transitional populations, refining models of planetesimal accretion, and collisional evolution.

How to cite: Fuentes, C. and Bommireddy, H.: Future of Mid-IR colors of sub-km asteroids from serendipitous JWST observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1532, https://doi.org/10.5194/epsc-dps2025-1532, 2025.

Interplanetary dust particles (IDPs), the source materials of the zodiacal light, are supposed to originate from comets and some asteroids (Vernazza et al. 2015 [1]). So far, our comprehension of their composition relies primarily on the analysis of IDPs collected in the stratosphere (e.g. Sandford 1989 [2]).

The Mid-InfraRed Instrument (MIRI) of the James Webb Space Telescope (JWST) has the capability to provide spectra of the zodiacal light at an unprecedented spectral resolution and across a broad spectral range, assuming it has a good signal-to-noise ratio (SNR), and therefore a sufficiently long acquisition time. Rather than dedicating observation time to zodiacal dust, it is possible to exploit backgrounds with long exposures times, such as those in the Cycle 2 GO program GO  2820 (PI: Pierre Vernazza).

This program includes six background fields associated with observations of the small objects (1) Bienor, (2) Chariklo, (3) 2020 VF1, (4) 2013 LU28, (5) 2002 GG166 and (6) 1999 OX3.

The data are reduced through the JWST calibration pipeline last version, which significantly reduces the fringing effect, especially for channels 3 and 4. In order to remove the thermal contribution from JWST, a synthetic background is generated based on JWST Backgrounds Tool (Rigby et al. 2023 [3]), depending on the time and location of the observation, and is rescaled to match the total observed background flux. Through these steps, the average SNR between 7µm  and 25 µm is above 100 across all datasets, thus allowing the detection of relatively weak spectral features.

Olivine and pyroxene features between 8 µm and 12 µm are detected and consistent with prior measurements from AKARI/IRC (Takahashi et al. 2019 [4]) , thereby enhancing the reliability of the features observed in MIRI spectra. Several significant features not related to olivine and pyroxene are detected. Over these six backgrounds, close in latitude, variation of intensity and shape of features are observed. These spectral differences are being assessed in relation to the DIRBE zodiacal model (Kelsall et al.1998 [5]) modelised by the ZodiPy Python package (San et al. 2022 [6]). 

This investigation will involve a comparison of these spectra with those of various IDPs (anhydrous and hydrous ; e.g. Sandford and Bradley 1989 [2]) and an exploration of potential links with major dust bands produced by recent asteroid break-ups (Brož et al. 2024 [7]) and Marsset et al. 2024 [8]).

References

[1] Vernazza et al. 2015, Interplanetary Dust Particles as Samples of Icy Asteroids. The Astrophysical Journal, 806(2):204, June 2015.

[2] Sandford and Bradley 1998, Interplanetary dust particles collected in the stratosphere: Observations of atmospheric heating and constraints on their interrelationship and sources. Icarus, 82(1):146–166, 1989.

[3] J. Rigby et al. 2023, How Dark the Sky: The JWST Backgrounds. Publications of the Astronomical Society of the Pacific, 135(1046):048002, April 2023.

[4] Takahashi et al. 2019, Mid-infrared spectroscopy of zodiacal emission with AKARI/IRC. Publications of the Astronomical Society of Japan, 71(6):110, 11 2019.

[5] Kelsall et al.1998, The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. II. Model of the Interplanetary Dust Cloud. The Astrophysical Journal, 508(1):44, nov 1998.

[6] San et al. 2022, COSMOGLOBE: Simulating zodiacal emission with ZodiPy.  A & A, 666:A107, 2022.

[7] Brož et al. 2024, Young asteroid families as the primary source of meteorites. Nature, 634(8034):566–571, Oct 2024. 

[8] Marsset et al. 2024,  The Massalia asteroid family as the origin of ordinary L chondrites. Nature, 634(8034):561–565, Oct 2024.

How to cite: Simon, P., Vernazza, P., Jorda, L., Ferrais, M., Binzel, R. P., DeMeo, F., Marsset, M., Beck, P., Anderson, S. E., and Brož, M.: Zodiacal Light Spectroscopy with JWST/MIRI, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-773, https://doi.org/10.5194/epsc-dps2025-773, 2025.

We present observations and analysis of Neptune’s atmosphere from JWST, providing new constraints on hydrocarbon abundances, cloud properties, and temperature structure across the planet’s disk.  

JWST observed Neptune in June 2023 (program1249) as part of the Solar System Guaranteed Time Observations (GTO). Integral field spectroscopy (IFS) with the Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument/Medium Resolution Spectrometer (MIRI/MRS) were combined to provide nearly simultaneous and continuous spatial and spectral data between 1.66 and 28.70 microns.

We show how wavelengths sensitive to the atmospheric temperatures reveal a structure consistent with Voyager [1] and ground-based imaging [2,3], with a sharply defined warm polar vortex. In contrast, wavelengths sensitive to stratospheric hydrocarbons (namely acetylene and ethane) show a marked enhancement in the northern winter hemisphere.

Finally, we examine the distribution and vertical structure of clouds in context of the temperature and chemical structure. Scattered light in NIRSpec observations indicate variable discrete clouds extend to pressures of roughly 50 mbar at the northernmost latitudes and south pole.

[1] Conrath, B. J., F. M. Flasar, and P. J. Gierasch. "Thermal structure and dynamics of Neptune's atmosphere from Voyager measurements." Journal of Geophysical Research: Space Physics 96, no. S01 (1991): 18931-18939.

[2] Fletcher, Leigh N., Imke de Pater, Glenn S. Orton, Heidi B. Hammel, Michael L. Sitko, and Patrick GJ Irwin. "Neptune at summer solstice: zonal mean temperatures from ground-based observations, 2003–2007." Icarus 231 (2014): 146-167.

[3] Roman, Michael T., Leigh N. Fletcher, Glenn S. Orton, Thomas K. Greathouse, Julianne I. Moses, Naomi Rowe-Gurney, Patrick GJ Irwin et al. "Subseasonal variation in Neptune’s mid-infrared emission." The Planetary Science Journal 3, no. 4 (2022): 78.

How to cite: Roman, M., Fletcher, L., Hammel, H., King, O., Orton, G., Rowe-Gurney, N., Irwin, P., Moses, J., de Pater, I., Melin, H., Harkett, J., Toogood, S., and Milam, S.: Temperature, Composition, and Cloud structure in Atmosphere of Neptune from MIRI-MRS and NIRSpec-IFU Observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1261, https://doi.org/10.5194/epsc-dps2025-1261, 2025.

Primitive C-complex asteroids, primarily located in the main asteroid belt, are commonly associated with carbonaceous chondrites (CCs) due to their low geometric albedo (typically p_v<10%) and similar spectral shape [e.g. 1]. The presence of hydrated minerals and organics in CCs attests to the accretion of volatiles by their parent body in the early solar system. These volatiles subsequently evolved through secondary processes, such as aqueous alteration. Thus, primitive asteroids are key witnesses for tracing the distribution and evolution of volatiles since solar system formation, as well as the role of primitive asteroids in Earth's water budget. Low-albedo collisional families of asteroids located in the inner main asteroid belt, between the ν₆ secular resonance at 2.1 au and the 3:1 mean motion resonance with Jupiter at 2.5 au, are likely the sources of primitive near Earth asteroids (NEAs) and CCs [e.g. 2]. Recently, two space missions, Hayabusa2 (JAXA) and OSIRIS-REx (NASA), collected and returned to Earth samples from two primitive NEAs, Ryugu and Bennu. Laboratory analysis of the samples and their contextualization in relation to primitive asteroids will be key to understanding the evolution of the solar system.

The aim of James Webb Space Telescope (JWST) SAMBA3 (Spectral Analysis of Main Belt Asteroids in the 3-µm region) program (General Observer program #6384, Cycle 3) led by Driss Takir, is to observe and analyze spectra of nine asteroids from the seven low-albedo and low-inclination (i < 15°) inner main belt families (New Polana, Eulalia, Erigone, Sulamitis, Clarissa, Chaldaea and Klio) with the NIRSpec instrument (0.97 – 5.10 µm). Primitive asteroids typically present featureless spectra in the 0.5-2.5 µm, with the exception of a shallow absorption at 0.7 µm attributed to Fe-rich phyllosilicates in some asteroids [3]. On the contrary, several diagnostic spectral features can be observed at wavelengths > 2.5 µm in spectra of primitive bodies, such as bands associated also with phyllosilicates at 2.7-2.8 µm, water ice around 3.1 µm, organics around 3.4 µm and carbonates around 3.4 and 3.9 µm [e.g. 4, 5, 6]. The inaccessibility of certain wavelengths in the infrared from ground-based observations, due to the atmospheric opacity, makes JWST essential for constraining the composition of primitive asteroids. Here, we aim at analyzing the reflectance spectra of the primitive asteroid (84) Klio, the largest member of the Klio family, with NIRSpec.

The observation of Klio was conducted on July 6, 2024. The data were calibrated using the JWST pipeline. The solar analog P330E (JWST program #1538, led by Karl Gordon) was used to separate the reflected and emitted components of the spectrum. The thermal emission was fitted using the Near-Earth Asteroid Thermal Model (NEATM, [7]), allowing us to estimate Klio’s diameter to 78.1 km. We then analyzed the reflectance spectrum in the 2.8, 3.4 and 3.9 µm regions. Different Gaussian fits were used to estimate the peak position and the amplitude of the features. Those spectral parameters give valuable information on the composition, in particular when compared with primitive samples analyzed in the laboratory. We thus compared Klio with reflectance spectra of samples of carbonaceous chondrites from Takir et al. [6,8], Ryugu samples from Pilorget et al. [9] and Bennu samples from Lauretta et al. [10]. We will present the result of this analysis, as well as the interpretation of Klio’s composition and the evolution processes undergone by its parent body. In particular, this study revealed significant spectral differences between Klio and the Bennu/Ryugu samples, reinforcing the hypothesis that Klio is an unlikely parent body for the Hayabusa2 and OSIRIS-REx targets.

Acknowledgements: We’d like to acknowledge the support of the Space Telescope Science Institute (JWST-GO-06384.001-A). TPJ, JdL, and JL acknowledge support from the Agencia Estatal de Investigacion del Ministerio de Ciencia e Innovación (AEI-MCINN) under grant "Hydrated Minerals and Organic Compounds in Primitive Asteroids" with reference PID2020-120464GB-100.

References:

[1] Campins, H., et al. 2018, in Primitive Meteorites and Asteroids, ed. N. Abreu (Elsevier), 345–369, [2] Broz, M., et al. 2024, A&A 689, [3] Vilas, F. & Gaffey, M. J. 1989, Science, 246, 790, [4] Campins, H., et al. 2010, Nature, 464, 1320, [5] Takir, D. & Emery, J. P. 2012, Icarus, 219, 641, [6] Takir, D. et al. 2013, Meteor. Planet. Sci., 48, 1618, [7] Harris, A. W., 1998, Icarus, 131, 291, [8] Takir, D., et al. 2019, Icarus, 333, 243, [9] Pilorget, C. et al. 2021, Nature Astronomy, 6, 221, [10] Lauretta, D. S., et al. 2024, Meteor. Planet. Sci., 59, 2453

How to cite: Le Pivert-Jolivet, T., de León, J., Licandro, J., Holler, B., Pinilla-Alonso, N., De Prá, M., Emery, J., Harvison, B., Masiero, J., McClure, L., and Takir, D.: Composition of asteroid 84 Klio with NIRSpec/JWST, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-359, https://doi.org/10.5194/epsc-dps2025-359, 2025.

Determining the distribution of water throughout the main asteroid belt can inform us about the formation and evolution of the early Solar System. A powerful method for probing water abundance involves the observation and characterization of carbon-rich (C-complex) asteroids in the “3-μm region,” which contains the fundamental OH stretching mode associated with hydrated or hydroxylated  minerals (Rivkin et al. 2002). Carbonaceous chondrites, the meteorite analogs for C-complex primitive asteroids,  generally exhibit the OH-strech from Fe- or Mg-rich phyllosilicates, which affect the band shape and center differently (Johnson & Fanale 1973; Takir et al. 2013).  The range in band parameters, in turn, aligns with the degree of aqueous alteration (Takir et al. 2013). Though ground-based observations of the 3-μm region are obstructed by Earth’s atmospheric water features, the James Webb Space Telescope (JWST) provides unmatched access to this crucial wavelength range. Additionally, JWST can access features longward of the 3-μm region that could be associated with water-ice, organics,  carbonates, or ammoniated phyllosilicates (Campins et al. 2010a; Rivkin & Emery 2010; Clark et al. 2009; Rivkin et al. 2022). Thus, JWST observations of C-complex asteroids in this region allow for insight into the formation and evolution of these bodies and the Solar System at large.

The Polana-Eulalia Complex (PEC) is a low-inclination, carbon-rich (C-complex) asteroid population residing in the inner Main Belt (IMB) among numerous other families (Walsh et al. 2013). As shown in Figure 1, the PEC is composed of two dynamically overlapping families centered around (142) Polana and (495) Eulalia, the largest members of each one. The nearby ν₆ secular resonance has likely caused some small PEC members to drift into near-Earth space. Notable examples of this dynamical evolution scenario include near-Earth asteroids Bennu and Ryugu, the targets of OSIRIS-REx and Hayabusa2 sample-return spacecraft missions, which are probabilistically traced back to the PEC region (Campins et al., 2010b, 2013; Bottke et al., 2015). Ground-based observational campaigns focused on near-ultraviolet (NUV; 0.35 – 0.46 μm), visible (VIS; 0.46 – 0.9 μm), and near-infrared (NIR; 0.9 – 2.2 μm) wavelengths found that members from both PEC families display featureless spectra (Tatsumi et al. 2022; de León et al. 2016, Pinilla-Alonso et al. 2016). Though PEC asteroids lack 0.7-μm features associated with Fe-bearing phyllosilicates, the presence of the fundamental OH-stretch from Mg-rich phyllosilicates in the 3-μm region cannot be ruled out (Rivkin et al. 2002; Takir et al. 2013). Spectral characterization in this wavelength region is particularly relevant to understanding the distribution of water throughout the Solar System as well as to disentangling the specific family of origin for Bennu and Ryugu.

Figure 1: The Yarkovsky Drift of the two families of the PEC, with asteroids Polana (red star) and Eulalia (blue star) at their relatively centralized orbital positions  (Vokrouhlický et al. 2006; Walsh et al. 2013).

In this work, we present a portion of JWST Cycle 3 spectra from Program #6384, led by Driss Takir. Entitled the “Spectral Analysis of Main Belt Asteroids in the 3-μm Region” (SAMBA3), this JWST program uses the NIRSpec instrument and has acquired spectra from (495) Eulalia and two ~10-km-sized Polana family asteroids: (6712) Hornstein & (2441) Hibbs. Upon calibrating the SAMBA3 spectra, we inspected/calculated spectral parameters for the observed features within and longward of the 3-μm region, including band shape and minimum. In addition to connecting the SAMBA3 spectra with VIS-NIR spectra of these objects, we compare PEC spectra to other relevant spectra, such as the spectrum of Bennu (remote & return-sample), of Ryugu (remote & return), and of (142) Polana (from Cycle 2 – Program #3760, PI A. Arredondo). We also contextualize the PEC spectra with the larger sample from this program, which also observed (84) Klio, (302) Clarissa, and (163) Erigone, largest members of the other carbon-rich, primitive-like families in the IMB.  Additionally, we link these PEC asteroid spectra to specific carbonaceous chondrite meteorite types.            

References:

Bottke, W. F., et al. (2015). Icarus, 247.

Campins, H., et al. (2010a). Nature, 464.

Campins, H., et al. (2010b). Astrophysical Journal Letters, 721.

Campins, H., et al. (2013). Astronomical Journal, 146(2).

Clark, R. N., et al. (2009). Journal of Geophysical Research: Planets, 114.

de León, J., et al. (2016). Icarus, 266.

Johnson, T. V. & Fanale, F. P., (1973). Journal of Geophysical Research, 78.

Pinilla-Alonso, N., et al (2016). Icarus, 274.

Rivkin, A. S., et al. (2002). Asteroids III.

Rivkin, A. S., & Emery, J. P., (2010). Nature,

Rivkin, A. S., et al. (2022). The Planetary Science Journal, 3, 153.

Takir, D., et al. (2013). Meteoritics and Planetary Science, 48(9).

Tatsumi, E., et al. (2022). Astronomy and Astrophysics, 664.

Vokrouhlický, D., et al. (2006). Icarus, 182(1).

Walsh, K. J., et al. (2013). Icarus, 225(1).

How to cite: McClure, L., Emery, J., Takir, D., Pinilla-Alonso, N., Harvison, B., De Prá, M., Holler, B., Le Pivert, T., de León, J., Licandro, J., and Masiero, J.: Compositional Characterization of the Polana-Eulalia Complex with JWST, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-404, https://doi.org/10.5194/epsc-dps2025-404, 2025.

Dynamically new Oort cloud comets, by their journeys into the inner solar system, deliver particulates and volatile gases into their comae that reveal records of the most primitive materials in the solar system. The abundances and spatial distribution of major gas species (H₂O, CO₂, CO), and organics yield insight into comet nucleus composition as well as sublimation or radiative dissociation of species in the coma. JWST spectroscopic observations of such comets provide a unique look into the physico-chemical properties of materials sublimed from the nucleus into the coma. Spectroscopy with MIRI MRS and NIRSpec integral-field-units (IFUs) deliver spectral-spatial cubes with wavelength access to key diagnostics of coma materials produced by comet nucleus sublimation activity, including molecular emission bands, organic signatures, and dust features in the spectral energy distribution (SEDs). Here, we highlight observations and modeling of a JWST study of the inner coma of the Oort cloud comet C/2017 K2 (PanSTARRS), a hyperactive (water ice active fraction ≥86%) comet at a heliocentric distance of 2.35 au. Our observations and analysis [1] reveals: (a) emission lines from H2O are detected in both NIRSpec and MRS spectra including faint H2O ro-vibrational lines from the ν₃-ν₂ and ν₁-ν₂ hot bands in the 4.5 to 5.2 μm range, and strong lines from the ν₂ fundamental vibrational band; (b) a wealth of trace volatile species (molecular emission) is superimposed on the continuum including CN (band emission centered at 4.9 μm), H₂CO, CH₃OH, CH₄, C₂H₆, HCN, NH₂, and OH prompt emission (after UV photolysis of water); (c) a particle differential size distribution (n(a)da) and relative abundances of amorphous carbon, amorphous silicates, and crystalline silicates commensurate with those found in other comets[2]. In C/2017 K2 (PanSTARRS) the average (spatially averaged across the coma) amorphous carbon mass fraction has a value of the order 0.247 ± 0.010, the silicate-to-carbon ratio is  of the order 3.049 ± 0.163, and the crystalline mass fraction of the sub-micron grains, f_cryst, is of the order 0.384 ± 0.065; (d) residual spectral emission features at 3.42 um and between 6.1 and 8.6 μm, with a prominent 6.9 um peak, in the JWST spectrum strongly support the contention that polycyclic aromatic hydrocarbons (PAHs) are present in the inner coma of this comet. We briefly discuss comparisons of the spectra of other comets observed with JWST early in the mission and explore the in-field and out-of-field impact of JWST comet surveys in the context of advancing our understanding of protoplanetary disk evolution and the formation of small bodies in the outer solar system. 

This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope Cycle 1 GO program 1556 whose analysis was supported via StSci grant JWST-GO-01566.001. 

References:[1] Woodward, C.E.  et al. 2025, “A JWST Study of the Remarkable Oort Cloud Comet C/2017 K2 (PanSTARRS)”, Planetary Sci. J. (in press) doi: 10.3847/PSJ/add1d5. [2] Harker, D.E. et al. 2024, “Dust Properties of Comets Observed by Spitzer”, Planetary Sci. J. 4, 242 doi: 10.3847/PSJ/ad0382.

How to cite: Woodward, C. E., Roth, N. X., Bockélee-Morvan, D., Wooden, D. H., Kelley, M. S. P., Harker, D. E., and Milam, S. N.: A JWST Spectroscopic Study of Comet C/2017 K2 (PanSTARRS), EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-488, https://doi.org/10.5194/epsc-dps2025-488, 2025.

Collisional impacts between asteroid-sized objects have been common throughout the history of our solar system and have significantly contributed to the formation of asteroid families (Nesvorný et al., 2015). Of particular interest are the low-albedo (geometric albedo < 0.10) and low-inclination (i ≤ 15°) asteroid families situated within the inner main belt (IMB), between the v₆ secular resonance at ~ 2.15 au and the 3:1 mean-motion resonance with Jupiter at ~2.5 au. These families are proposed to be significant sources of carbonaceous near-Earth asteroids (NEAs) such as asteroids Ryugu and Bennu (Bottke et al. 2015; Granvik et al. 2016; Dykhuis and Greenberg, 2015). Carbonaceous NEAs contain abundant water- and carbon-rich materials, which are essential elements for understanding the origin of life on Earth and provide valuable historical records of the early solar system. Exploring the relationships between carbonaceous NEAs and these IMB families also enhances the scientific value of the sample return missions (see this meeting abstract # 678 by Takir et al.).  Studying the IMB also has broader implications for the formation of exoplanetary systems, such as PDS 70. The discovery of water vapor by JWST MIRI in the inner part of PDS 70’s protoplanetary disk (Perotti et al. 2023) suggests that water is playing a crucial role in the formation of this young exoplanetary system.

As part of the JWST SAMBA3 (Spectral Analysis of Main Belt Asteroids in the 3-µm region) program (Cycle 3 GO; #6384), we are conducting observations of asteroids from seven collisional low-albedo and low-inclination families located in the IMB. The studied families include New Polana, Eulalia, Erigone, Sulamitis, Clarissa, Chaldaea, and Klio. We have selected nine asteroids from these families to investigate potential links with carbonaceous NEAs (see Table 1). Our study focuses on the parent bodies of six asteroid families. For the New Polana family, we are observing three fragments. We will compare these fragments with one another and with the parent body asteroid (142) Polana (Arredondo et al. 2024) to determine whether the fragments from the same family exhibit similar or differing hydration states (e.g., Michel et al. 2020). For our observations, we are utilizing the NIRSpec instrument, which covers a spectral range of~ 0.6 to 5.2 µm. This range includes essential diagnostic absorption features characteristic of primitive and carbonaceous materials, such as H₂O/hydroxyl (OH), carbonates, and organics.

Table 1. Current JWST observation status of the SAMBA3 program (Cycle 3 GO; #6384).

As of this writing, JWST has executed observations for seven asteroids. The observation of asteroid (6769) Brokoff faced an issue and was not fully executed; therefore, it has been rescheduled for the next cycle. Le Pivert-Jolivet et al. (this meeting abstract #359) will discuss the analysis and interpretation of asteroid (84) Klio. Harvison et al. (this meeting abstract #1004) will focus on asteroids (302) Clarissa and (163) Erigone. Additionally, McClure et al. (this meeting abstract #404) will examine asteroids (2441) Hibbs, (6712) Hornstein, and (495) Eulalia. We also expect to observe asteroids (752) Sulamitis and (313) Chladaea before the meeting.

Acknowledgements: We would like to acknowledge the support of the Space Telescope Science Institute (JWST-GO-06384.001-A). JdL, TPJ, and JL acknowledge support from the Agencia Estatal de Investigacion del Ministerio de Ciencia e Innovación (AEI-MCINN) under grant "Hydrated Minerals and Organic Compounds in Primitive Asteroids" with reference PID2020-120464GB-100.

References:

Arredondo, A. et al., 2024. AAS DPS, Abstract##411.02.

Bottke, W.F et al., 2015. Icarus 247, 191e217.

Dykhuis, M., Greenberg, R., 2015. Icarus 252, 199e211.

Granvik, M. et al., 2016. Icarus 312, 181-207.

Michel, P. et al., 2020. Nature Communications 11, 2655 (2020.

Nesvorný, D. et al., 2015.  Asteroids IV 297e321.

Perotti, G. et al., 2023 et al.  Nature 620, 516-520.

How to cite: Takir, D., de Prá, M., de León, J., Emery, J., Harvison, B., Holler, B., Le Pivert-Jolivet, T., Licandro, J., Masiero, J., McClure, L., and Pinilla-Alonso, N.: SAMBA3: A JWST Program to Study Low-albedo and Inclination Inner Main Belt Asteroid Families and their Connection to Carbonaceous Near-Earth Asteroids, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-761, https://doi.org/10.5194/epsc-dps2025-761, 2025.

Primitive asteroids in the Main Belt possess one of the most pristine inventories of materials in the Solar System. Main Belt primitive asteroids are particularly interesting due to clear evidence of phyllosilicates, i.e., silicates that have encountered liquid water and undergone chemical alteration. Since asteroids are thought to be likely contributors to Earth's water content [1-3], mapping hydration across the primitive asteroid population is essential for understanding the compositional structure of the early Solar System and the introduction of water on Earth. Low-albedo (pv < 10%) and low-inclination (i < 10°) primitive asteroid families in the inner Main Belt are dynamically linked to the primitive NEAs Ryugu and Bennu [4,5], further supporting the importance of investigating their composition and the dynamics responsible for their delivery to near-Earth space. The Cycle 3 Program, “Low-Albedo and Inclination Asteroid Families as Tracers for Water and Organics in the Inner Solar System,” is currently conducting observations using the James Webb Space Telescope (JWST) to investigate this category of primitive bodies directly. Utilizing JWST’s NIRSpec Integral Field Unit (IFU), the program is acquiring near-infrared spectra (0.6 – 5.2 µm) from the largest bodies in the Clarissa, Erigone, and Sulamitis asteroid families. 

Initial investigations into the visible spectra of the Erigone, Sulamitis, and Clarissa families identified a specific trend regarding Fe-rich phyllosilicates: the Erigone and Sulamitis families exhibited similar, high percentages of members showing the 0.7 μm band, indicative of this mineral (60%). In contrast, an extremely low percentage of members expressed the feature in the Clarissa and Polana families [6]. While the absence of a 0.7 μm feature may initially suggest no hydration, it does not provide sufficient grounds to conclude that the body is not hydrated, as Mg-rich phyllosilicates do not show this feature. Studies have shown that although some asteroids lack the 0.7 μm feature, they may still exhibit the 3.0 μm region, whereas all asteroids with a 0.7 μm feature display the 3.0 μm band [7]. This region has been notoriously hard to observe from ground-based observatories due to the Earth’s water-rich atmosphere. JWST observations are required to adequately constrain these bodies' thermal and compositional histories. We will present the compiled preliminary investigations of JWST NIRSpec spectra of (163) Erigone, (302) Clarissa, and (752) Sulamitis. We will search for diagnostic features of hydrated minerals, complex organics, and carbonates. Each spectral feature will be characterized by band center, depth, and area, and compared to features identified in the spectra of carbonaceous chondrite meteorite analogs to investigate possible relationships. Finally, we will explore the compositional diversity of inner belt primitive families and how this connects to their formation and evolutionary history.

References: [1] Marty, B. (2012). Earth and Planetary Science Letters. [2] Piani, L. et al. (2020). Science. [3] Mezger, K. et al. (2021). Icarus. [4] Campins, H. et al. (2010). The Astrophysical Journal. [5] Campins, H. et al. (2013). The Astronomical Journal. [6] Morate, D. et al. (2018). Astronomy and Astrophysics. [7] Rivkin, A. et al. (2015). The Astronomical Journal.

How to cite: Harvison, B., De Prá, M., Pinilla-Alonso, N., Takir, D., Le Pivert-Jolivet, T., Licandro, J., de Leon, J., Holler, B., Emery, J., McClure, L., and Masiero, J.: (163) Erigone, (302) Clarissa, and (752) Sulamitis as seen with JWST’s NIRSpec, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1004, https://doi.org/10.5194/epsc-dps2025-1004, 2025.

Comets are amongst the most primitive bodies in the solar system, containing volatile ices and dust particles from eras of protoplanet formation. Multiple perihelion passages of comets into the inner solar system cause a stratification of volatiles within their nuclei, with the most volatile ices preserved at greater depths. Comet nuclei also evolve from the redeposition of particles not lost from their gravity fields. On their first sojourns into the solar system, dynamically new Oort cloud comets offer important opportunities to study their comae volatiles and dust particles less encumbered by nuclei evolution.

Comet C/2017 K2 was one such dynamically new Oort cloud comet. Observations of comet K2 by the James Webb Space Telescope (JWST) at 2.35 au provided an ideal opportunity to search for polycyclic aromatic hydrocarbons (PAHs) in its coma [1]. High signal-to-noise ratio NIRSpec and MRS spectra were obtained. Emission bands centered at 3.42 µm, 6.9 µm, and 8.55 µm, and a plateau 6.3—8.6 µm, were identified and modeled with the Ames PAHdb Python Suite utilizing an excitation energy of 5770K appropriate for the Sun. PAHs with multiple hydrogens on their peripheral bonding sites were found to be very important in explaining the spectrum of comet K2 [1]. Such PAHs have been described as ‘aliphatic PAHs’ [2], PAHs with –CH₂ side groups, and H_n-PAHs or ‘moderately hydrogenated’ PAHs [3]. PAHs embedded in water ice may have acquired additional H atoms, and PAHs in water ice irradiated with UV generate PAH cations, and these cations persist upon water ice sublimation [1].

The broad spectral coverage of NIRSpec and MRS was crucial for modeling thermal dust emission from coma particles [4, 5], necessary for determining the baseline beneath potential PAH bands [1]. Figure 1 shows the best-fit thermal model fitted to MRS 4.9—27 µm SED (F_λ  vs. λ) after subtraction of an extrapolated scattered light component fit derived from the NIRSpec spectrum. A notable 3.42 µm feature, not accounted for by the NASA Planetary Spectrum Generator (PSG) molecular emission line model, was considered in modeling PAH emissions. The ‘PAH extract’ residual spectrum was computed as the MRS flux minus the emission lines, scattered light, and thermal model ‘F(total)’, and then median filtered (shown in navy in Fig. 1).

Figure 1. Spectral decomposition of flux of comet K2: NIRSpec (gray); PSG-fitted molecular emission lines subtracted (cyan) and then filtered (blue, cf. [1]);  NIRSpec scattered light fit (yellow) extrapolated to MRS (gold); MRS best-fit thermal model fitted to the scattered-light-subtracted flux (‘F(total)’, red) and extrapolated to NIRSpec (red). The residual (violet-red) and median filtered residual (navy) contain  PAH emissions. Dust emissions from high-temperature oxides such as those from CAIs may explain the residual at 12.5-16.5 µm.  (Adapted from [1])

Figure 2 shows the best-fit PAHdb model for comet K2 using a 5770 K (blackbody) excitation cascade and restricted to PAHs with less than 101 carbon atoms (N_C<=100). Heavily hydrogenated PAHs, characterized by  –CH₂ side groups (N_CH2 >0) [3], are present in the coma of comet K2. The Rosetta Mission ROSINA mass spectrometer detected aromatic molecules in comet 67P/Churymov-Gerasimenko (67P), although the fragmentation signatures were not sufficiently prominent to allow identification at >~35 atoms: ROSINA detected hydrogenated PAHs with N_C=10 spanning normal hydrogenation to fully hydrogenated (C₁₀H₈ Naphthalene through C₁₀H₁₈ Decahydronaphthalene) [6]. ROSINA detected linear chain organic molecules, heterocycles, and PAHs in the ratios of 6:3:1 [6].

Figure 2. Model for PAH emissions in comet K2. Heavily hydrogenated PAHs, characterized by  –CH₂ sidegroups (N_CH2 >0) [3], are present in the coma of comet K2. (b) Small (N_C≤40) neutral PAHs fit the isolated 3.42 µm feature. (c) Small cations and large (N_C>40) neutrals primarily contribute to the 6.9 µm and 8.55 µm features, and the emission plateau. Large neutrals and cations contribute. The upcoming PAH database v4.0 will have more large PAHs. (Adapted from [1].)

Based on their comparison of the organics to those in the ISM using the diagram of Hydrogen Deficiency Index versus N_atoms (for comet K2, see Fig. 24 in [1]) for comet 67P versus ISM sources, Hanni et al. [6] conclude that cometary organics have an ISM heritage with evolution. The PAHdb model for K2 extends to larger N_atom than ROSINA.  Comet K2 has PAHs not as fully hydrogenated as comet 67P, yet supports the Hanni et al. view of potential inheritance from the ISM. The formation of PAH cations and hydrogenation of PAHs in water ice may provide a natural explanation of hydrogenated PAHs in cometary comae. High sensitivity JWST NIRSpec and MRS observations of more comets are needed to deepen our understanding of the evolution of aromatic molecules in the protoplanetary disk at the comet-forming epoch.

This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope Cycle 1 GO program 1556 whose analysis was supported via STSci grant JWST-GO-01566.003-A.

References:

[1] Woodward, C.E. et al. 2025, A JWST Study of the Remarkable Oort Cloud Comet C/2017 K2 (PanSTARRS), Planetary Sci. J. (in press) arXiv:2504.19849

[2] Yang, X. J., et al. 2016, On the aliphatic versus aromatic content of the carriers of the ‘unidentified’ infrared emission features, MNRAS 462, 1551 doi:10.1093/mnras/stw1740

[3] Sandford, S. A., et al. 2013, The Infrared Spectra of Polycyclic Aromatic Hydrocarbons with Excess Peripheral H Atoms (H_n-PAHs) and their Relation to the 3.4 and 6.9 µm PAH Emission Features, ApJS 205:8 doi:10.1088/0067-0049/205/1/8

[4] Harker, D.E. et al. 2024, Dust Properties of Comets Observed by Spitzer, Planetary Sci. J. 4, 242 doi:10.3847/PSJ/ad0382

[5] Bockelee-Morvan, D., et al. 2024, Chemical and Physical Properties of Cometary Dust, in Comets III, ed. K. J. Meech et al., Space Sci. Ser., U. AZ Press. doi:10.48550/arXiv.2305.03417

[6] Hänni, N. et al. 2022, Identification and characterization of a new ensemble of cometary organic molecules, Nature Comm. 13:3639 doi:10.1038/s41467-022-31346-9

How to cite: Wooden, D., Woodward, C., Bockelee-Morvan, D., Harker, D., Roth, N., Kelley, M., and Milam, S.: JWST Discovers Heavily Hydrogenated PAHs in the Coma of the Dynamically New Oort Cloud Comet C/2017 K2 (Pan-STARRS), EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1109, https://doi.org/10.5194/epsc-dps2025-1109, 2025.

Motivation: Ceres, Pallas, and Hygiea are the three largest low-albedo objects in the main asteroid belt, and contain a little more than half of the belt’s mass. Ceres has been visited by the Dawn spacecraft, which has shown it to be a geologically varied relict “Ocean World” and dwarf planet, with cryovolcanism perhaps still occurring today [1,2]. Hygiea appears to be a spectral twin of Ceres, suggesting a similar composition (and perhaps a similar history?). Pallas, by contrast, is thought to be more consistent with the carbonaceous chondrite meteorites, and could plausibly be the largest undifferentiated object in the solar system.  The launch of JWST provided the opportunity to extend the wavelength coverage of these objects into spectral regions unobservable from Earth, and to use Dawn’s visit to Ceres to calibrate quantitative estimates of hydrogen content from these, and future, observations.

Observations: Two instruments were used for the observations: the Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI).  In both cases an integral field unit (IFU) was used. The observations were made as part of GTO program 1244, part of a larger GTO effort spearheaded by Heidi Hammel. Observations took place on 1 August 2022 (Hygiea MIRI and NIRspec), 1 October 2022 (Pallas NIRSpec), 17 December 2022 (Pallas MIRI), and 18 January 2023 (Ceres MIRI and NIRSpec). 

NIRSpec: The NIRSpec data were downloaded from the Mikulski Archive for Space Telescopes (MAST) and processed using typical methods for IFU observations that are detailed in the literature [3-5, etc.]. Because all three targets are extended sources for the NIRSpec IFU (ranging from 2.3 pixels for Hygiea to 6.4 pixels for Ceres), boxes of 13 pixels for Ceres and 9 pixels for Pallas and Hygiea were used, encompassing ~98% of calibrated flux, though the final analyses were done on normalized spectra so the results are insensitive to the absolute flux calibration.  The spectra of Ceres and Pallas were saturated beyond roughly 3.7 and 3.2 µm, respectively, and those spectral sections were not analyzed. It is possible that some of the saturated wavelength regions can be recovered (see below), but the wavelength regions uniquely observable by JWST (2.5—2.85 µm) were unsaturated.  Following spectral extraction, the thermal flux contribution was calculated for each object and removed, resulting in a reflectance-only spectrum for analysis.  

All three objects have an absorption band near 2.72 µm, with Hygiea and Ceres showing band centers at identical wavelengths that only differ by 0.001 µm from Pallas’s band center. This is interpreted as due to Mg-OH indicating very Mg-rich phyllosilicates. Ceres and Hygiea additionally show features near 3.05 µm and 3.31 µm, with band centers that differ by < 0.01 µm. These are interpreted as due to NH₄⁺ in minerals. In the 3-µm region, the two differ mainly in band depths, with Ceres showing a relatively deeper band due to NH₄⁺than the OH band, suggesting Ceres has a more NH₄⁺ -rich mineralogy than Hygiea. Ceres and Hygiea appear practically identical across all wavelengths that have been studied, not only in the JWST data but in other wavelengths by other workers. This similarity opens the intriguing possibility that Ceres and Hygiea had similar histories and processes, though modeling of Hygiea’s history will be necessary to demonstrate whether that was likely. 

The NIRSpec data were also used to estimate the hydrogen content in the regolith of Ceres, Pallas, and Hygiea, with results suggesting concentrations of roughly 0.5-1 weight percent, consistent with what is seen in CM chondrites.

MIRI: The sensitivity of JWST/MIRI and the brightness of Ceres, Pallas, and Hygiea at mid-infrared wavelengths combine to make it impossible to collect a completely unsaturated spectrum across all wavelengths with any setting. With this in mind, the observations were undertaken with an eye to analyzing those wavelength regions that were unsaturated and understanding the conditions where saturated data could be usefully recovered.

After exploring sophisticated recovery techniques, we determined that many such techniques that estimate the brightness of saturated pixels [6] were foiled by JWST’s very tight PSF. In this situation, the surrounding non-saturated pixels had low enough signal compared to the central pixel that extrapolating to the central pixel flux was not robust. As a result, our initial analyses focus on extracting the SED of the unsaturated pixels and scaling them to match unsaturated spectral segments where there is overlap.

We will discuss the NIRSpec results and the current state of the MIRI analysis. 

References: [1] Scully, Jennifer EC, et al. The Planetary Science Journal 2.3 (2021): 94. [2] Ruesch, O., et al. Science 353.6303 (2016): aaf4286. [3] Emery, J. P., et al. Icarus 414 (2024): 116017. [4] Wong, Ian, et al. The Planetary Science Journal5.4 (2024): 87. [5] Rivkin, Andrew S., et al. The Planetary Science Journal 6.1 (2025): 9. [6] Pope, B. J. S., et al. Monthly Notices of the Royal Astronomical Society: Letters 455.1 (2015): L36-L40.

How to cite: Rivkin, A., Wong, I., Glatzberg, A., Thomas, C., Holler, B., Pope, B., and Hammel, H.: JWST Measurements of the Three Largest Low-Albedo Asteroids, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1219, https://doi.org/10.5194/epsc-dps2025-1219, 2025.