Thibault Cavalié

The Submillimetre Wave Instrument (SWI) onboard the Jupiter Icy Moons Explorer (Juice) spacecraft consists of a 29 cm off-axis paraboloid antenna and two double-sideband heterodyne receivers operating in the frequency ranges of 530–638 and 1066–1286 GHz. This instrument is designed to study Jupiter's atmosphere and the exospheres of the Galilean moons. We used the Lunar-Earth-Gravity-Assist (LEGA) data from August 2024 to characterise this antenna using several SWI observations pointing towards the Earth. The data analysis of the LEGA observations dedicated to the antenna beam allows us to characterise the antenna beam Full Width at Half Maximum (FWHM), sidelobes, absolute pointing and receiver coalignement. Moreover, an estimate of the calibration efficiency factor has been obtained from an optical model simulation.

Context. The formation of Uranus and Neptune remains poorly constrained, largely due to poorly known deep elemental abundances. Carbon monoxide (CO), a disequilibrium species in the upper troposphere, provides an indirect constraint on the deep oxygen abundance. Aims. We wish to improve our knowledge of the deep O/H and C/O ratios of the ice giants and their impact on formation scenarios by accounting for meridional variations in the atmospheric structure and assessing the impact of chemical uncertainties on these ratios. Methods. We extended a 1D thermochemical and diffusion model into a pseudo-2D model by including the latitudinal variation in several key input model parameters. The deep oxygen abundance was inferred by matching the modeled CO mole fractions to observations in the upper troposphere and was compared to the deep carbon abundance to compute the C/O ratio. Results. For Uranus, varying the tropospheric methane mole fraction alone yielded O/H ~[47–57]× protosolar, whereas allowing K _zz to vary expanded the inferred range to O/H ~[62–177]× protosolar. For Neptune, the corresponding sets of simulations led to O/H ~[182–215]× protosolar and O/H ~[222–342]× protosolar, respectively, supporting the hypothesis that oxygen is depleted in Uranus relative to Neptune. This agrees with previous works. The uncertainties associated with the chemical network introduce a more modest effect that amounts to ~10% of the retrieved oxygen ranges at most. The uncertainties are on the same order as the uncertainty associated with the measurement of the CO abundance on Neptune, and they are higher on Uranus. We computed C/O latitudinal ranges and found C/O ~ [0.06–0.52] on Uranus and C/O ~ [0.02–0.12] on Neptune. When compared with a protoplanetary disk model, these results suggest a different formation or evolution pathway for Uranus and Neptune. Conclusions. The results highlight the dominant role of vertical mixing in constraining the deep oxygen abundance of Uranus and Neptune, and they demonstrate the importance of accounting for meridional variability and chemical kinetic uncertainties. This work provides a framework for selecting the latitude entry of a future Uranus Orbiter and Probe mission.

On 19 and 20 August 2024 the Jupiter Icy Moons Explorer (Juice) executed during its cruise phase towards Jupiter a combined Lunar Earth Gravity Assist (LEGA) maneuver. These close flybys of the Moon and the Earth provided so far the best opportunity to test the behavior, performance, and calibration of the Submillimetre Wave Instrument (SWI) onboard Juice. This paper shows typical data taken during the Earth Gravity Assist and the following few days. Data quality and problems resulting from unexpected behavior of the hardware are discussed.

We present visible-to-infrared (0.5–5.56 μ m) observations of the interstellar comet 3I/ATLAS obtained with the Moons and Jupiter Imaging Spectrometer aboard the Jupiter Icy Moons Explorer spacecraft between 2025 November 2 and 25, shortly after perihelion. The fluorescence emission from H ₂ O at 2.7 μ m and CO ₂ at 4.3 μ m is detected at heliocentric distances of 1.36–1.68 au. A weak dust-scattered continuum is identified from which we determine the spectral slope, with values ranging from ∼15% per 100 nm in the 0.65–0.9 μ m region to 1%–3% per 100 nm from 0.9 to 2.6 μ m. Spatially resolved measurements show that the radial distributions of H ₂ O and CO ₂ species are consistent with release in the near-nucleus environment. We derive H ₂ O production rates that decreased from 8 × 10 ²⁸ s ⁻¹ to 4 × 10 ²⁸ s ⁻¹ over the period November 2–25, while the CO ₂ /H ₂ O ratio remained nearly constant at ∼10%. The heliocentric evolution of the CO ₂ production rate indicates activity controlled by solar heating. Combined with published CO measurements and the low gas expansion velocities, our analyses support a scenario in which CO ₂ plays a major role in driving the activity of 3I/ATLAS near perihelion. In addition, broad emission features are identified in the 3.2–3.6 μ m region that cannot be explained by the fluorescence of common cometary CH–bearing volatiles. Their spectral characteristics are consistent with aliphatic C–H functional groups and provide tentative evidence for the release of complex organic material from dust grains in the coma.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On 19 August 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km s ⁻¹ relative to the Sun. On 20 August 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km s ⁻¹ relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 µm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

JUICE (JUpiter ICy moons Explorer) is the first large mission in ESA’s Cosmic Vision 2015-2025 programme. The spacecraft was launched on April 2023 and will arrive at the Jupiter system in July 2031. The primary science goals of the mission are to characterize the Jovian icy satellites, studying their surfaces and interiors to unveil their history and internal structures, and to assess the emergence of habitable environments in their internal oceans [1]. To reach those goals JUICE will perform a complex series of orbits around Jupiter in which it will also run an extensive series of observations of the planet’s atmosphere [2], its magnetosphere and the ring system. All previous Jupiter missions since Galileo have benefited from extensive ground-based campaigns with a variety of telescopes and observational capabilities. A brilliant example of those collaborations comes from NASA’s Juno mission, which has requested collaboration with amateurs for a full decade, enhancing the spatial context and investigations in the time domain of various instruments with a particular strong participation with the Juno camera [3]. In this regard, amateur observations of Jupiter have demonstrated the capability to provide an excellent coverage of atmospheric phenomena that serve as spatial and temporal context to the close observations from spacecraft instruments or space telescopes. Databases of amateur observations such as ALPO Japan (https://alpo-j.sakura.ne.jp/indexE.htm) and PVOL (http://pvol2.ehu.eus/) [4] serve the science community providing access to the amateur data. Open source software tools popular in the amateur community (WinJupos, available at https://jupos.org/) [5] or more python-oriented tools such as PlanetMapper [6] support the analysis of amateur data. In addition, ESA’s Planetary Science Archive (https://archives.esac.esa.int/psa/#/pages/home) releases public data obtained by the two monitoring cameras (JMC; Juice Monitoring Camera 1 and 2) and will soon release also data from the navigation camera (NAVCAM). Data from the science instruments will be released through ESA’s Planetary Science Archive after proprietary time.In this contribution, we discuss the interest of the mission and its Jupiter Atmosphere Working Group to receive observational support from amateur astronomers. This support is needed during the years before Juno and JUICE to continue understanding temporal changes in the atmosphere of the planet. During the JUICE mission, particular needs will arise over different periods. For example, over the first year of the mission JUICE orbits will be eccentric with larger apojoves implying longer periods of time between close perijoves. Later, orbits will have high-inclinations with reduced views of the equatorial latitudes and in the year before Ganymede orbit insertion orbits will be more regular but constrained by Data Volume. We expect that JUICE collaboration with amateur astronomers will broaden public involvement in the mission and will enhance outreach activities of the mission.With Jupiter having a negative declination over 2031-2035 when observed from Earth, observations from the southern hemisphere and equatorial latitudes will be favored. Thus, specific outreach activities targeting amateur astronomy in the Global South may improve the amateur collaboration in the mission. Jupiter’s south declination implies that amateur observers in Japan, European countries and the US, where most experienced observers actively participating in collaborations with Jupiter researchers reside, will observe Jupiter under low elevations. Thus, we will actively promote knowledge of the mission in South America and Africa, where amateur astronomy is popular but Jupiter observations are less frequent. We expect to identify JUICE science activities that can be promoted within partners such the Astronomical Society of Southern Africa, the Asociación Argentina Amigos de la Astronomía and Sociedad Astronómica de Valparaiso y Viña del Mar. Such activities can be fostered with the help and participation of international societies promoting astronomy worldwide. Key partners toward that effort are The Europlanet Society and the International Astronomical Union Outreach Group. We will also seek a global collaboration with traditional actors in the amateur planetary astronomy world including the British Astronomical Association Jupiter Section, the Association of Lunar and Planetary Observers and planetary imaging communities on well-known international forums such as Cloudy Nights.References[1] Grasset et al. JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system. Planetary and Space Science, 78 (2013). [2] Fletcher et al. Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer. Space Science Reviews, 219 (2023). [3] Hansen, C.J., et al. Junocam: Juno’s Outreach Camera. Space Sci Rev 213, 475–506 (2017). [4] Hueso et al. The Planetary Virtual Observatory and Laboratory (PVOL) and its integration into the Virtual European Solar and Planetary Access (VESPA). Planetary and Space Science, 150 (2018). [5] Jacquesson and Mettig. JUPOS: Amateur analysis of Jupiter images with specialized measurement software. European Planetary Science Congress (2008). [6] King and Fletcher, PlanetMapper: A Python package for visualizing, navigating and mapping Solar System observations. Journal of Open Source Software, 8 (2023).

Giant planet atmospheres are continuously affected by external sources, including cometary impacts, interplanetary dust particles (IDPs), and material originating from rings and satellites, that modify their composition over long timescales. At Jupiter, the last major comet impact occurred in July 1994, when the 21 fragments of comet Shoemaker–Levy 9 (SL9) collided with the planet in its southern hemisphere over the course of one week (Noll et al. 1996). This rare event provided a unique opportunity to investigate the shock-induced chemistry recombining jovian atmosphere and cometary material, leading to the detection of several new species in Jupiter’s stratosphere (e.g., CO, CS, and HCN; Lellouch et al. 1996).On longer timescales, monitoring these newly formed species months and years after the impacts provides valuable constraints on the chemical and dynamical evolution of exogenic material in Jupiter’s atmosphere. First, the temporal evolution of their abundances traces the chemical loss processes. For instance, Cavalié et al. (2023) reported an HCN loss of a factor of 2–8 in 2017 ALMA observations compared to the 1995–1998 period. Second, their horizontal and vertical transport constrains atmospheric dynamics and mixing as a function of longitude, latitude, and altitude. At first located at the impact sites, the longest-lived species progressively spread in longitude over a few months, in latitude over a few years (e.g., Lellouch et al. 2006; Moreno et al. 2003), and vertically from pressures near 0.1 mbar initially to several mbar (Cavalié et al. 2023; Rodriguez-Ovalle et al. 2025). Owing to horizontal mixing, these molecules were expected to become uniformly distributed across Jupiter’s disk on a timescale of about 10 years (Moreno et al. 2003). This prediction was confirmed in 2017 for CO, which exhibited a constant latitudinal distribution (Cavalié et al. 2023).However, HCN exhibits an unusual distribution from the mid-latitudes to the polar regions (Cavalié et al. 2023; Rodriguez-Ovalle et al. 2025). This behaviour is unexpected because HCN and CO share the same cometary origin and should therefore display similarly uniform distributions. Two remarkable features were identified by Cavalié et al. (2023). First, they observed an HCN depletion towards the poles, coincident with the position of the auroral regions. This depletion is seen vertically at pressures greater than 0.1 mbar and has been tentatively attributed to adsorption onto aerosols forming and growing at these pressure levels in the polar atmosphere (Friedson et al. 2002). Second, and more surprisingly, HCN exhibits a high-altitude abundance enhancement reaching up to 20 times the low-to-mid latitude abundance. This enhancement is spatially confined to the southern auroral hot spot (Sinclair et al. 2023) at 0.01 mbar, i.e., above the pressure levels where depletion is observed in the polar regions. Such an HCN enhancement could result from local production through ion–neutral chemistry under auroral conditions.In this study, we aim to monitor the temporal evolution of SL9-produced species in the stratosphere of Jupiter, in order to (i) follow their horizontal and vertical transport to constrain the mixing properties at the probed levels; (ii) constrain the chemical losses over time ; and (iii) assess their distribution in the polar regions and understand the auroral related chemistry.We use mapping observations of Jupiter performed with Atacama Large Millimeter/submillimeter Array (ALMA) recorded on three occasions in September 2022, i.e., almost 30 years after the SL9 impacts. We detect the HCN (J=4-3), CO (J=3-2), and CS(J=7-6) emission lines emanating from the stratosphere of Jupiter all along the planetary limb. While HCN and CO were already observed with ALMA in 2017, we present the first high resolution map of CS. Here, we will present radiative transfer calculations and vertical profile retrievals performed at various latitudes to illustrate the horizontal and vertical distributions of the targeted species. We will compare our results with those obtained from observations performed over the last 30 years.References:Cavalié et al. 2021, A&A 647, 8Cavalié et al. 2023, Nat. Astron. 7, 1048Friedson et al. 2002, Icarus 158, 389Lellouch 1996, IAU 156Lellouch et al. 2006, Icarus 184, 478Moreno et al. 2003, P&SS 51, 591Noll et al. 1996, Cambridge University PressRodriguez-Ovalle et al. 2025, A&A 696, 173Sinclair et al. 2023, Planet. Sci. J. 4, 7

Uranus and Neptune are the most distant and the least explored planets within our solar system. To this day, the formation history of these ice giants remains uncertain. A better understanding of their deep atmospheric composition helps to constrain where and how these planets formed within the protoplanetary disk. Remote sensing can only retrieve the atmospheric composition down to the few bar level in the millimeter to infrared domain, and an entry probe as part of the Uranus Flagship mission may only measure the atmospheric composition down to ~10-20 bars. Some species are measured in this upper-tropospheric region at abundances several order of magnitude above what is predicted by thermochemical equilibrium. Atmospheric models are thus needed to interpret how the measured abundances of such species reflect the deeper atmospheric composition. Using a thermochemical & diffusion model (Cavalie et al., 2024), we aim to take advantage of such disequilibrium species to further constrain Uranus's and Neptune's deep atmospheric compositions. We have updated the model to consider the meridional variability of several parameters in the troposphere, including a formulation for the eddy diffusivity coefficient, Kzz, based on convection under rotation laboratory experiments. We provide a range of plausible deep O/H ratios for both planets, as well as assess the impact of uncertainty propagation in a large chemical network on such ratios. We compute C/O ratios as a function of latitude, and compare them with a protoplanetary disk model results (e.g. Schneeberger et al. 2023) that tracks the time-dependent radial transport of solids through the disk. Our results suggest a different C/O between Uranus and Neptune and thus may support a different formation pathway for the ice giants.

The Jupiter Icy Moons Explorer (JUICE) is the first L-class mission of the Cosmic Vision 2015-2025 program of the European Space Agency. JUICE was launched in April 2023 and embarked on an 8-year interplanetary transfer to reach Jupiter and its system. It will perform its Jupiter orbit insertion in July 2031 and start its nominal science phase. JUICE will orbit the planet about 60 times until its Ganymede orbit insertion (GOI) at the end of 2034. This Jupiter tour will comprise 2 close flybys of Europa, and many more flybys of Ganymede and Callisto. After starting the Jupiter tour in the equatorial plane of the planet, JUICE will spend many months in inclined orbits reaching inclinations of up to ~ 35 degrees before going back to the equatorial plane in preparation of GOI.The payload of JUICE comprises 10 science instruments. One of the remote sensing instruments is the Submillimetre Wave Instrument (SWI), which was designed to study the composition, chemistry and dynamics of the atmospheres of Jupiter and the Galilean Moons. It will also investigate the surface properties of the moon surfaces. SWI is an off-axis single dish telescope with 29 cm diameter equipped with two perpendicular pointing mechanisms that allow to point ±72° along track and ±4.3° cross track from the nadir direction of the JUICE platform during the Jupiter tour. It is a heterodyne spectrometer and radiometer that can be tuned independently and simultaneously in two submillimetre bands (530-638 GHz and 1066-1286 GHz). The highest spectral resolution is achieved with the Chirp Transform Spectrometers that cover 1 GHz bandwidth with 10000 channels. SWI is thus a miniaturized observatory with all the inherent complexity implied for observation planning.The JUICE Science Operation Center (JSOC) is conducting planning exercises every year before JOI. These exercises serve the purpose of developing the science observation implementation procedures and the relevant software tools (both at the ESA and instrument team levels) that will ensure smooth operations during the science phase. In parallel, the four JUICE science working groups are continuously consolidating and extending the JUICE science objectives. They also identify multi-instrument synergies and propose coordinated observation campaigns.The latest planning exercise occurred in the first semester of 2026 and focused on two equatorial orbits, namely orbits 37 and 38, that include a close Ganymede flyby. It spans from 23 November to 20 December 2033, with the flyby occurring on 27 November 2033. The flyby inbound is mostly on the nightside and the outbound on the dayside, with a closest approach at ~900 km altitude. The orbits also provide opportunities for Io, Europa and Callisto observations with apparent sizes sufficiently large so that enable to map them.The implementation of the JUICE observing plan follows a multi-step approach (observation plan, pointing timeline, instrument timeline) coordinated by JSOC. A significant effort by JSOC and the instrument teams concerned the identification and implementation of common/complementary observations in the design the spacecraft pointing profile to maximize the science return of the mission in these orbits and flyby. Following the latest JUICE science synergy workshop (ESAC, January 2026), several coordinated campaigns have been implemented in the 2026 planning exercise and helped making the implementation of the timeline more efficient. Of particular interest for SWI are the following coordinated campaigns: zonal winds, distant monitoring and auroral monitoring for Jupiter, and a coordinated mapping of the Ganymede dayside on the flyby outbound leg.For what concerns SWI, the observation sequences pre-defined are complemented with other SWI observations, that can be either prime or ride-along observations. For Jupiter, those include: (i) temperature and winds observations with Jupiter limb scans, (ii) searches for isotopes and new species with limb stares and scans, (iii) temperature and composition measurements by means of regional mapping observations (including the auroral regions). During the flyby Ganymede, SWI will perform surface and exosphere regional mapping observations from the largest distances during the flyby and a series of limb stares and scans to investigate the composition, temperature and winds of its exosphere a few hours from closest approach. Moreover, SWI aims to conduct a monitoring of the Galilean Moons surfaces and exospheres on a daily basis, dedicating about 1 hour per day of operations, to investigate the various processes acting as sources and sinks for the exospheres. Finally, SWI will support observation campaigns initiated and led by other instruments and the latest planning exercise proposed several examples of those, like: (i) stellar and Earth radio occultations for which SWI will observe the temperature, composition and winds of the target at the latitudes/longitudes of the ingress/egress, and (ii) Io and Europa closest distance observations.

The Submillimeter Wave Instrument (SWI) aboard the JUpiter Icy Moon Explorer (JUICE) satellite conducted a series of dedicated observations of the Moon and Earth atmosphere as part of an instrument characterization and calibration campaign during the Lunar-Earth Gravity Assist maneuver in mid-August 2024. The JUICE satellite achieved an altitude of approximately 700 km during its closest approach, while subsequent moon observations were conducted at distances of around 500,000 km. The lunar atmosphere was observed in both nadir and limb geometries in the two bands of SWI (600 and 1200 GHz). Although no direct signature of the water line was detected in the data, these observations allowed upper limits to be placed on the neutral water column density. We proceed to summarize the measurement, modeling approach, and its underlying assumptions, followed by a discussion of the implications for the moon's water cycle.