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Abstract:

The Great Red Spot (GRS) is one of the most prominent features observed on Jupiter due to its size and distinctive colour, yet many aspects of this vortex remain poorly understood. Fundamental questions regarding the vertical structure, the chromophores responsible for its colour, the distribution of such chromophores and other aerosols remain unanswered. Laboratory experiments in which ammonia (NH3) and acetylene (C2H2) are photolyzed by ultraviolet radiation (Carlson et al. 2016) may provide a solution for the identity of the chromophore. One study suggested that this chromophore could be responsible for the red colour across the whole disk of Jupiter, giving rise to the idea of a “universal chromophore” (Sromovsky et al. 2017), which may be located at the top of the main tropospheric cloud, resembling a “crème brûlée” structure (Baines et al. 2019). Other studies suggest that, while the universal chromophore could be plausible, it may not be the one caused by the NH3‒C2H2 reaction, instead it would be one with a steeper blue absorption gradient (Braude et al. 2020). Alternatively, some studies propose the presence of two chromophores located in both an upper haze and lower haze layer, with the upper haze chromophore possibly corresponding to that produced by the NH3‒C2H2 reaction (Anguiano‐Arteaga et al. 2021; Anguiano‐Arteaga et al. 2026).More generally, observations indicate that the top of the GRS is located at a higher altitude than the surrounding cloud deck. Consequently, vertical structure models developed for the rest of Jupiter’s disk may not provide accurate solutions for the vortex itself, where each atmospheric layer may be shifted to higher altitudes. We are analysing observations of the GRS obtained by VLT/MUSE (0.480 – 0.930 µm), Cassini/VIMS (0.884 – 5.122 µm), Juno/JIRAM (2.002 – 5.014 µm), and JWST/NIRSpec (1.660 – 3.170 µm, 2.870 – 5.270 µm), using the radiative transfer model ArchNEMESIS (Alday et al. 2025). The usage of multiple instruments, different geometries and a wide wavelength range aims to better constrain the vertical structure and chromophore distribution of the GRS, as well as those of other vortices of interest on Jupiter.

Abstract:

Recent JWST transmission and emission spectroscopic observation of hot Jupiters have demonstrated that sub-micron sized silicate mineral clouds may be common hot Jupiter atmospheres. In addition, ground-based high-resolution spectroscopic observations of both transit and eclipse have implied horizontal asymmetries that may be amplified by clouds. Silicate mineral clouds have long been predicted to form and persist on the nightside and western dayside of hot Jupiters by cloud microphysical models and 3D General Circulation Models. Given the capability of current ground-based high resolution spectrographs, complementary JWST observations, as well as recent advancements in modelling techniques, the time is right to determine the prevalence and spatial and particle size distribution of mineral clouds across the parameter regime of hot Jupiters. This effort will provide a detailed test of our present theoretical understanding of cloud nucleation, transport and growth processes, and the radiative feedback of clouds on the atmospheric circulation and climate of hot Jupiters. In this work, we present a combination of analytical and numerical models of the vertical mixing of mineral clouds in hot gas giant atmospheres. Our scaling analyses naively predict that clouds of a broad range of particle sizes (up to 10 microns) should be well-mixed throughout gas giant atmospheres to low pressures (~0.1 mbars). However, the local nature of vertical mixing in more detailed three-dimensional simulations prevents such well-mixed micron-sized mineral clouds in many cases. In addition, we hypothesise that fragmentation may play a role in setting the characteristic maximum particle size of silicate mineral clouds in hot Jupiter atmospheres, much like it impacts the build-up of silicate grains in protoplanetary disks. We predict how mixing scales with cloud particle size and composition using analytic theory and three-dimensional numerical simulations including cloud tracers. We discuss implications for ground-based high resolution characterisation of hot Jupiters, especially with time-resolved spectroscopy.

Abstract:

Analysing observations of Jupiter made by VLT/MUSE (0.475 – 0.933 μm), Cassini/VIMS (0.40 – 5.15 μm), and Juno/JIRAM (2 – 5 μm), we present early results of a new combined cloud-ammonia profile model for Jupiter's equatorial atmosphere. We find this model to be consistent with all observations considered, at a range of observation geometries, within the Equatorial Zone (EZ), the North Equatorial Belt (NEB) and a North Equatorial Dark Feature (NEDF), also known as a '5-micron-hotspot'. Preliminary results suggest the presence of three main layers: 1) a deep 'Cloud-1' at 1-2 bar; 2) an upper 'Cloud-2' in the upper troposphere based at ~0.55 bar; and 3) a layer of chromophore particles situated within the Cloud-1 layer, responsible for the blue-absorption at visible wavelengths.  Our best-fit ammonia profile is closely linked with our cloud profile, with Cloud-1 coinciding with a sharp drop in ammonia abundance, perhaps associated with the formation of a H2O-NH3 'mushball' cloud, or an ammonium hydrosulphide (NH4SH) cloud, or both, and Cloud-2 coinciding with the ammonia condensation level.We find the bulk of the cloud opacity in Jupiter’s atmosphere to be in the Cloud-1 layer, based at 1-2 bar and composed of relatively large particles (r ~ 10 μm), which are highly scattering at visible wavelengths to allow sunlight to penetrate and be Rayleigh-scattered from the deeper atmosphere, but more absorbing at 5 μm. The belt/zone difference at 5 μm is accounted for by changes in the opacity of Cloud-1 and also the single-scattering albedo of these particles. We find the Cloud-2 layer, based at the ammonia condensation level, to be approximately 10 times less opaque than Cloud-1 and have an absorption band near 3 μm, which is consistent with this layer having a significant opacity of large (r ~ 10 μm) ammonia ice particles.We will present preliminary insights into the spatial distribution of these clouds over the regions considered and their implications for our understanding of Jupiter’s chromophores and upper-level hazes.

Abstract:

We present a calibrated catalog of Cassini Visible and Infrared Mapping Spectrometer (VIMS) observations of Jupiter, together with the processing workflow used to generate the final publicly available products. Starting from the raw VIMS cubes, the workflow produces radiometrically consistent multiextension Flexible Image Transport System files and includes a revised visible-channel calibration, a revised infrared-channel calibration that resolves a subset of problematic cases not satisfactorily treated by the standard Integrated Software for Imagers and Spectrometers pipeline, corrections for pointing-related misalignments between spectral cubes and geometric backplanes, and customized dark signal correction strategies. The final products include calibrated spectral cubes together with geometry backplanes and wavelength information for subsequent scientific analysis. We assess the consistency of the calibrated products through internal validation tests and comparisons with independent reference spectra from the literature. The resulting products provide a uniform and validated data set of Cassini VIMS Jupiter observations for community use. The full catalog is available as a public dataset at doi:10.5281/zenodo.19223781.