The cryospheres of ice-covered ocean worlds (i.e., their surfaces and solid ice layers) represent a new frontier in our understanding of the functioning and evolution of planetary systems. Cryospheres govern ocean-surface interaction and play active roles in the evolution and habitability of icy worlds. Furthermore, icy world cryospheres show evidence for a fascinating spectrum of geological activity that is unique to this class of world. Dynamic processes such as ‘cryovolcanic’ plumes or brine extrusions offer immense promise for exploration, as they may transport liquids from the subsurface to the surface environment where they can be studied by spacecraft. Indeed, salts and other endogenic materials have been detected at the surfaces of Enceladus, Europa, Ganymede and Ceres, indicating that some ocean to surface transport takes place. However, interpreting the archive of ocean chemistry recorded at icy world surfaces requires accounting for how the composition of ocean materials is influenced by cryosphere processes. Many of these processes have no direct analogy in silicate rocky planetary systems, meaning new frameworks are required. This challenge can be met by integrating studies of Earth’s cryosphere with laboratory simulations.

I will present results from studies of experimental and natural analogues that provide insight into the potential chemical diversity generated by dynamic processes in icy world cryospheres. I will show how permafrost-hosted brine seeps in the High Arctic can help us understand how ocean composition and evidence of habitability could be transported and altered by ice-hosted brines. I will describe laboratory investigations into how salts emplaced from subsurface fluids can influence long-term evolution of icy world surface features. Finally, I will highlight recent laboratory discoveries of novel hydrates that show how the thermal history of frozen fluids can be recorded in their mineralogical composition. Together, this work provides new frameworks for interpreting surface composition of icy worlds that can be used by upcoming missions such as NASA's Europa Clipper and ESA's JUICE to identify regions of recent fluid delivery to the surfaces of icy worlds.

How to cite: Fox-Powell, M. G.: Liquid processes within icy world cryospheres: Insights from experimental and natural analogues, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22901, https://doi.org/10.5194/egusphere-egu26-22901, 2026.

How to cite: Cheng, A., Wolfenbarger, N., and Schroeder, D.: Constraining the thermophysical structure and composition of Europa’s ice shell through radar detection of eutectic interfaces, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14742, https://doi.org/10.5194/egusphere-egu26-14742, 2026.

Surface properties like porosity and grain sizes on icy moons remain poorly understood, despite decades of remote sensing observations. Spaceborne instruments do not measure the ice microstructure directly: instead, they record proxy measurements (such as thermal flux or reflectance spectra) which are then interpreted through modeling to estimate thermal inertia, porosity, grain size, etc... However, from data acquisition to parameter inversion, these models rely on various assumptions and simplifications. As a result, different studies using the same raw data but distinct modeling approaches can give different estimates for the same physical parameters, making it difficult to place a robust constraint on the true surface characteristics of the ice.

This study takes a different approach by exploring the parameter space of values that are physically incompatible with icy moon conditions. Notably, the consistently low thermal inertia (<20 SI from Howett et al. 2010) measured at the very top surface of all icy moons is far below that of bulk crystalline water ice (~2000 SI). While a lower thermal conductivity could be attributed to the mix of insulating materials (e.g., dust or amorphous ice phases) regions of pure crystalline ice also exist on these bodies and yet they still present such low thermal inertia near the surface.

Through physics-based reasoning on this data, we demonstrate that pure crystalline water ice can only achieve such low thermal inertia through a combination of very high porosity (>80%), small grain sizes (<1 mm) and an unconsolidated regolith (minimal bond sizes).Tighter or looser constraints can be derived depending on the assumptions underlying the various models found in the literature, which are also discussed. By defining the range of allowed porosities and grain sizes, these constraints will help Bayesian inversion modeling in spectroscopy (Cruz-Mermy et al. 2025) including for future MAJIS (JUICE) and MISE (Europa Clipper) spectrometers, as well as for the planning of rover operations and landing site selection on such highly porous surfaces (e.g., Voyager2050, ESA’s L4 mission).

How to cite: Mergny, C.: The Low Thermal Inertia of Icy Moons: Implications on Surface Porosity, Grain Size, and Regolith Structure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21185, https://doi.org/10.5194/egusphere-egu26-21185, 2026.

While the geysers on Enceladus are a spectacular example of explosive cryovolcanic eruptions, active cryovolcanic effusions have not been observed in the Solar System. Signs of former cryoeffusions are only indirect, including smooth terrains with morphological resemblance to volcanic flows on Earth (Fagents, 2003; Lesage et al., 2020), thermal anomalies (Abramov and Spencer, 2009), or excess atmospheric volatiles (Quick et al., 2017). As a result, our ability to investigate the processes involved in their emplacement remains limited.

Several theoretical models have been proposed to explain and describe the origin and behavior of effusive cryovolcanism, that is, the ascent and release of subsurface water onto the surface (Allison and Clifford, 1987; Quick et al., 2017; Lesage et al., 2020). In general, water exposed to the cold, near-vacuum surface environments of icy bodies is expected to freeze with a porous skin (Bargery et al., 2010). A vast uncertainty remains, however, regarding how long it takes, how much material is lost due to vaporization and sublimation, and how porous the resulting ice is (Morrison et al., 2023; Brož et al., 2025).

In the presented work (Patočka et al., 2026), we expose 40 kg of low-salinity water in a specialist chamber at The Open University, UK, and show that freezing under near-vacuum conditions is a complex, dynamic process during which vapor puffs through the growing ice sheets, building previously unobserved ice structures. Millimeter-thin, sheet-like ice layers form, separated by centimeter-thick, large-aspect-ratio pockets of vapor. The overall height of this layered, bubble-rich ice is controlled by a balance between its weight and the equilibrium vapor pressure. In the laboratory, the height reaches approximately ten centimeters, which could plausibly extend to tens of meters in the low-gravity environments of icy bodies. The high porosity of such ice has significant implications for the interpretation of remote sensing observations, and its fragile character makes terrains created by effusive cryovolcanism hazardous for spacecraft landing. 

This work was funded by the Czech Grant Agency grant No. 25- 15473S. VP has been supported by the Charles University Research Centre program No.~UNCE/24/SCI/005. MRP acknowledges support from the UK Space Agency/STFC through grants UKRI2545, ST/X006549/1, ST/Y005929/1, ST/Y000234/1 and ST/X001180/1.

References:

Abramov, O., Spencer, J.R., 2009, doi:10.1016/j.icarus.2008.07.016.
Allison, M., Clifford, S., 1987, doi.org/10.1029/JB092iB08p07865
Bargery, A.S., Lane, S.J., Barrett, A., Wilson, L., Gilbert, J.S., 2010, doi:10.1016/j.icarus.2010.06.019.
Brož, P., Patočka, V., Butcher, F., Sylvest, M., Patel, M., 2025, doi:10.1016/j.epsl.2025.119531.
Fagents, S.A., 2003, doi:10.1029/2003JE002128.
Lesage, E., Massol, H., Schmidt, F., 2020, doi:10.1016/j.icarus.2019.07.003.
Morrison, A.A., Whittington, A.G., Mitchell, K.L., 2023, doi:10.1029/2022JE007383.
Patočka, V., Brož, P., Chan, K., Sindhu, P., Fox-Powell, M., Sylvest, M., Emerland, Z., Patel, M., 2026, submitted

How to cite: Patočka, V., Brož, P., Chan, K., Sindhu, P. B., Fox-Powell, M., Sylvest, M., Emerland, Z., and Patel, M.: Layered bubble-rich structures on icy worlds: experiments with large volumes of low-salinity water in near-vacuum environment., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7016, https://doi.org/10.5194/egusphere-egu26-7016, 2026.

We ask what may drive Europa’s putative intermittent plumes. We test whether shallow pockets of liquid water (i.e., sills) freezing within Europa's ice shell can power activity. We build a numerical model that couples heat flow, phase change, and pressure evolution, including the drop in melting temperature under pressure. As a sill freezes, the expansion of ice raises pressure; when a fracture opens, pressure falls and any supercooled liquid crystallizes quickly, producing bursts of solidification, pressure release, and re-pressurization. This cycle can yield sporadic venting and seismic events without a sustained conduit. Pressure-dependent melting shortens the total freezing time at depth and produces rarer but larger events, while elastic flexing of the ice roof reduces the event rate. For reasonable sill sizes and numbers, our model predicts late-stage spikes consistent with sporadic plumes and low-magnitude quakes. These results identify freezing sills as a self-contained engine for Europa’s activity and provide testable signatures for upcoming missions to seek Europaquakes and plumes.

How to cite: Ojha, L.: Europaquakes and Plumes Powered by Freezing-Driven Overpressure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14210, https://doi.org/10.5194/egusphere-egu26-14210, 2026.

Jupiter’s moon Ganymede, the largest moon in the Solar System, is the main focus of the JUICE mission, which will observe its surface and measure its interior with unprecedented detail (Van Hoolst et al., 2024). In contrast with smaller moons such as Europa or Enceladus where an ocean is in contact with the silicate interior, Ganymede contains a high pressure (HP) ice layer between its ocean and the rocky core. Thus, on Ganymede, the dynamics in the high pressure ice layer control the exchange of heat and chemical species between the ocean and rocky interior.

The thickness of the HP ice layer is not well constrained, and interior structure models suggest thicknesses around 400 km, with values as low as 100 km (Kalousova et al., 2018) and as high as 700 km (Vance et al., 2018). Depending on the thickness of this layer, various polymorphs of HP ice might appear (Hussmann et al., 2015), such as ice V and ice VI, and for a sufficiently cold ocean also ice III (Journaux et al., 2020). Here we focus on ice V and ice VI, as they might exhibit different viscosities that in turn can substantially affect the convective behavior of the HP ice layer. Rheological experiments of ice V and ice VI are rare, but existing studies (Sotin & Poirier, 1987) indicate that ice V can be harder to deform than ice VI, and the viscosity ratio can reach up to three orders of magnitude.

We investigate the dynamics of Ganymede’s HP ice layer using the geodynamical code GAIA (Hüttig et al., 2013). Our models use the viscosity formulation of Kalousová et al. (2018) that has been derived from rheological experiments (Sotin et al., 1985; Durham et al., 1996). We test models where the HP ice layer of Ganymede is subdivided into ice V and ice VI layers. Our models vary the reference viscosity of the ice VI layer between 10¹⁵ and 10¹⁸ Pa s and apply a viscosity contrast between the ice V and ice VI layers of up to 1000. Similar to Choblet et al. (2017), we limit the temperature to the melting temperature of the HP ice layers and compute the amount of melt produced throughout the evolution. Our models consider a decaying heat flow boundary condition at the ice-rock boundary using values from Choblet et al. (2017), and assuming that the heat flow exponentially decreases from 40, 20 or 10 mW/m² at 4.5 Gyr ago to a present-day value of 5 mW/m².

Our models show that the ice shell dynamics substantially change with the increase of viscosity contrast between ice V and ice VI, leading eventually to a two layered convection structure. Heat and material transport from the ice-rock interface to the ocean occurs in pulses, when convective plumes can penetrate through the upper, high-viscosity ice V layer. Future models will include the effects of tidal heating and track the redistribution of impurities, i.e., salts, through the high pressure ice layers of Ganymede.

How to cite: van den Heuvel, N., Plesa, A.-C., Hussmann, H., and Sotin, C.: Geodynamics of the High Pressure Ice Layer on Ganymede, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-538, https://doi.org/10.5194/egusphere-egu26-538, 2026.

Zonal jets are coherent east-west winds or currents observed –or expected to emerge– in many planetary fluid layers, from the Earth’s oceans and atmosphere, to the atmospheres of gas giants, the subsurface oceans of icy moons and the liquid metallic cores of telluric planets. In many of these systems, zonal jets interact with a solid boundary with topography: the bathymetry in Earth’s oceans is known to influence the dynamics of the Antarctic Circumpolar Current, flows in liquid cores interact with the topography at the Core-Mantle boundary, and icy moon oceans are in direct contact with a global ice crust of spatially varying thickness.

In this talk, I will present laboratory experiments to study the interaction between self-sustained turbulent zonal jets and an isolated topography. We use the Coreaboloid device at UCLA (Lonner et al., 2022, doi:10.1029/2022JE007356) to robustly produce turbulent zonal jets. The setup is a 75cm-diameter water tank rotating at speeds up to 72 revolutions per minute. The deflection of the free surface due to the fast rotation provides a strong topographic β-effect. The flow is forced by thermal convection, driven by starting the experiment with hot water, and cooling the inner cylinder with a block of ice. To simulate a localised topography, we attach acrylic disks of different radii and heights on the bottom plate. We visualise the flow using 1) a thermal infrared camera to image the temperature field at the free surface 2) particle image velocimetry (PIV) on a horizontal laser plane and 3) ultrasonic doppler velocimetry (UDV) along three chords. We find that stationary Rossby waves develop downstream of the topography in prograde jets and influence the amplitude, number, and position of the zonal jets. The observed zonal wavelength of stationary lee Rossby waves agrees with theoretical predictions for plane Rossby waves, provided that the feedback of the zonal flow amplitude and curvature is taken into account. Remarkably, the topography leaves a visible imprint on the flow even for heights as small as h=3 mm, corresponding to just 1.2% of the total fluid depth H. For larger topography (h/H=5.9% to 17.5%), upstream blocking is observed, and a cyclonic circulation forms above the topography.

How to cite: Lemasquerier, D., David, C., Monville, R., and Aurnou, J.: Turbulent zonal jets interacting with isolated topography: an experimental study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11571, https://doi.org/10.5194/egusphere-egu26-11571, 2026.

Inertia waves are considered a potential source of oceanic dissipation in deep fluid interiors such as the oceans icy satellites or the convective envelopes of stars. The geometry of a finite ocean, together with the reflecting properties of inertia waves, allows periodic paths called attractors to accumulate large amounts of energy eventually balanced by viscous dissipation. The interaction of these wave attractors with convective plumes at the pole and mid-latitudes is studied with 3D MITgcm simulations. Strong convection is found to inhibit energy accumulation along wave attractors as the inertia wave beam is decohered. A range of temperature gradients and wave beam properties is explored to approach a scaling law for the critical Rayleigh number below which inertia wave beams may be sustained.

How to cite: Abdulah, D. and Kang, W.: Inertial waves in a convecting ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15159, https://doi.org/10.5194/egusphere-egu26-15159, 2026.

Because of Jupiter’s rotation and the orbital motion of the Galilean moons, the subsurface oceans experience a time varying magnetic field. This gives rise to magnetic induction of electric currents, and the measurement of the related magnetic fields lead to the discovery of the subsurface oceans. The complex orbital motions yield magnetic field variations of different frequencies, with different amplitudes and phases that both change over time. Analyzing the orbital evolution, we provide a catalogue of these important parameters, which are crucial for interpreting the measured induced magnetic fields.

The interaction of the electric currents with the magnetic field results in Lorentz forces, which drive flows in the oceans. We perform numerical simulations of this process and identify two types of induced flows: 1) persistent axisymmetric westward flows and 2) flows reminiscent of inertial modes, which are typical for the dynamics of rotating systems. An attempt to scale our simulations to the ocean properties suggests that the flow amplitudes remain much slower than convective driven flows.

How to cite: Wicht, J. and De Langen, I.: Inducing Fields and Lorentz force driven flows in the subsurface oceans of icy moons, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17345, https://doi.org/10.5194/egusphere-egu26-17345, 2026.

Acetylene (C₂H₂) is the most abundant solid product of methane photochemistry in Titan’s stratosphere. Unlike ethane (C₂H₆), it does not form a liquid under surface conditions. It should be widespread across Titan’s surface, and yet it hardly, if at all, appears in VIMS spectroscopic data. Where is the acetylene? Both chemical and physical processes are at play on the surface. Preliminary results from a production-loss-transport model of acetylene showing substantial depletion of pure acetylene on the equatorial and mid-latitude regions of Titan are presented. Production is by atmospheric photochemistry and sedimentation in aerosols to the surface. Solid acetylene is metastable and so physical disturbances (see below) can induce cyclization to benzene (C₆H₆) or polymerization to various forms of polyacetylene (with interesting physical properties).  Reaction with surface HCN (produced by atmospheric chemistry in somewhat lesser amounts) or other nitriles or imines at first glance would be thermally inhibited, but recent calculations of quantum tunneling under Titan conditions suggests acceleration of reaction rates by many orders of magnitude, and so that chemistry is included here. Physical transport is latitudinal, by sublimation/condensation (acetylene is volatile enough to be moved from equator to pole on timescales of 10⁵ years), and from highlands to lowlands by mechanical transport during the intense methane rainfall events observed by Cassini. Aeolian processes, including particle growth (to the sand-sized material in the dunes) and triboelectric charging are included. Static discharge and mechanical disturbance due to aeolian and fluvial processes provide the disturbances to include cyclization or polymerization.   The variation of sunlight through axial precession is relevant on the timescale of sublimation.  Surface gardening by micrometeoroids is unimportant because of the thick atmosphere. Localized processes around lakes and seas, such as dissolution and co-crystal formation, will have a small effect on the overall global budget of acetylene. The predicted abundances and geographic distribution of the acetylene and its products will inform JWST spectroscopic observations and the in-situ investigations by Dragonfly.

Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

How to cite: Lunine, J. I.: The Physical and Chemical Life Cycle of Acetylene on Titan’s Surface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13920, https://doi.org/10.5194/egusphere-egu26-13920, 2026.

As a plausibly habitable Solar System “ocean world”, Jupiter’s moon Europa is a key target for ongoing and future exploration [1]. A fundamental habitability requirement is the provision of bioavailable Phosphorus (P), one of six elements (CHNOPS) essential for all known life that is vital for the formation of phospholipids, the structural framework of DNA and RNA, and energy production and transfer. However, the delivery, abundance, and speciation of P into Europa’s subsurface ocean is currently entirely unconstrained.

Phosphorus is a limiting nutrient on Earth [2], as P is less abundant than other CHNOPS elements and P reservoirs are dominated by the poorly soluble phosphate (P(V) as PO₄^3-) mineral apatite. While present at lower abundances, reduced P species phosphite (P(III)) has significantly greater solubility and reactivity, and hence bioavailability, than phosphate [2-3]. As such, phosphite has been argued to represent an important P source in early Earth and extraterrestrial aqueous environments [3-5]. Several geological pathways exist to produce and liberate phosphite. Most pertinent to Europa is serpentinisation [5], where water-rock reaction of ultramafic and mafic lithologies at the mantle-ocean interface may i) reduce lattice-bound phosphate substituting for SiO₄ in olivine to phosphite and/or ii) liberate magmatic phosphite lattice-bound in Mg-Fe silicates. Though ultramafic and mafic rocks possess low bulk P contents, their likely lithological dominance in differentiated icy moons means serpentinisation is a viable mechanism for bioavailable P delivery to subsurface oceans [5].

Following the methods of [3] and using loss of ignition (LOI) as a proxy for water/rock ratios and degree of serpentinisation, we constrain P speciation in variably serpentinised ultramafic to mafic lithologies from the Troodos ophiolite, Cyprus. Preliminary data reveal variable but ubiquitous phosphite in mantle and crustal samples (P(III)/P(V) ≤0.01 to 0.45). In variably serpentinised harzburgites, increasing P(III)/P(V) correlates with LOI, supporting serpeninisation-driven liberation of phosphite, via either reduction of phosphate or preferential release of magmatic phosphite. Furthermore, an observed decrease in P(III)/P(V) above 15 % LOI supports the thermodynamic models of [5], which imply an upper limit to the water/rock ratios permissive for these reactions. These data indicate serpentinisation-driven reduction of phosphate and/or liberation of magmatic phosphite is a resolvable and ubiquitous process in natural materials analogous to Europa’s rocky ocean floor, providing further constraints on the habitability of Europa’s subsurface ocean.

[1] Vance et al. (2023), Space Science Reviews 219, 81. [2] Duhamel (2024) Nature Reviews Microbiology 23, 239-255. [3] Baidya et al. (2024), Communications Earth & Environment 5(1), 491. [4] Baidya et al. (2025) Nature Communications 16, 4825. [5] Pasek et al. (2022), GCA 336, 332-340.

How to cite: Staddon, L. G., Cousins, C. R., Baidya, A. S., Kalita, J., Stüeken, E. E., and Mappin, N.: Serpentinisation-driven liberation of bioessential phosphite (P(III)) in Europa-relevant lithologies., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17296, https://doi.org/10.5194/egusphere-egu26-17296, 2026.

Enceladus and Europa are key targets for planetary exploration due to their subsurface water oceans, making them some of the most habitable places in the solar system. Onboard the Europa Clipper spacecraft, the SUrface Dust Analyzer (SUDA [1]) will provide the chemical composition of ice grains ejected by plumes and/or micrometeorite bombardment of the surface. As shown by laboratory experiments [e.g., 2,3], molecular biosignatures can be detected by SUDA or an alternative advanced mass spectrometer on an Enceladus mission [4]. Lipids in particular can provide characteristic spectral fingerprints and are considered universal biomarkers of life [5] owing to their effective membrane-forming properties even under geochemically hostile conditions and their ubiquity in all known forms of life.

The performance and calibration of SUDA-type instruments strongly relies on analogue experiments using Laser Induced Liquid Beam Ion Desorption (LILBID) - a well-established method allowing the simulation of ice grains’ impact ionization mass spectra. Many LILBID spectra have already been recorded to complement an expanding reference database [6] for e.g., Europa Clipper.Environmental samples allow for a more realistic assessment of the detection capabilities of spaceborne instruments (as compared to experiments with prepared synthetic samples of well-defined compositions). Specifically, natural ice analogues from polar locations offer some of the most realistic representations of icy moons. However, polar samples have never before been analyzed with LILBID.

Here we present the first analysis of natural ice analogues with LILBID combined with a detailed characterization of lipid biomarkers. With support from the Instituto Antártico Uruguayo, ice samples were collected from key locations in the Collins (a.k.a. Bellingshausen) glacier on King George Island, Antarctica, where several environmental conditions (including intense UV radiation, saline aerosols, low temperature) are analogous to specific processes on ocean worlds.

LILBID analysis, providing SUDA-type analogue mass spectra, were combined to data obtained from Gas Chromatography linked to Mass Spectrometry (GC-MS), Raman and IR spectroscopy. Results on icy samples containing pink microalgae revealed key fingerprints of lipids adapted to cold temperatures, and highlight a novel assessment of the detectability of lipid biomarkers from icy moon analogues with spaceborne instrumentation.

[1] S. Kempf et al., Space Sci. Rev. 221, 10 (2025); [2] M. Dannenmann et al. Astrobiology 23(1):60–75 (2023); [3] F. Klenner et al., Science Advances, 10(12), eadl0849 (2024); [4] O. Mousis et al., The Planetary Science Journal, 3(12), 268 (2022); [5] C.D. Georgiou & D.W. Deamer. Astrobiology 14(6):541–549 2014); [6] F. Klenner et al., Earth Space Sci., 9, e2022EA002313 (2022)

How to cite: Napoleoni, M., Hortal Sánchez, L., Finkel, P. L., Carrizo, D., Sánchez-García, L., Burr, D., Hofmann, F., Moreno Paz, M., Khawaja, N., Parro, V., and Postberg, F.: Identification of Molecular Biosignatures in Antarctic Ices: Implications for Icy Moons Exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11450, https://doi.org/10.5194/egusphere-egu26-11450, 2026.

The ESA Voyage 2050 Senior Committee recommended a mission to the “Moons of the Giant Planets” as ESA’s fourth Large-class mission (L4), building on the legacy of Cassini-Huygens and JUICE. ESA’s leadership in planetary science is reaffirmed through this bold initiative to explore ocean worlds and search for biosignatures.

Following this recommendation, ESA convened an Expert Committee to define the mission’s scope. Enceladus emerged as the prime target due to its active plumes and potential for in-situ ocean sampling. Cassini’s 2005 flybys revealed water vapour jets and ice particles erupting from Enceladus’ south pole, with magnetometer data confirming subsurface activity. Surface temperatures around the “tiger stripes” reached −163°C, indicating geological heat sources and active cryovolcanism.

Enceladus meets all three criteria for habitability: liquid water, energy, and essential chemical elements. ESA’s L4 mission will advance this legacy by deploying both an orbiter and a lander—marking the first landing attempt on Enceladus. The lander will analyse icy particles precipitating from the subsurface ocean, potentially rich in salts, organics, and biosignatures.

Since March 2025, ESA’s study team, in collaboration with the Payload Working Group and Expert Committee, has been refining science requirements and identifying enabling technologies. This mission will push European capabilities in in-orbit assembly, extreme environment operations, landing systems, and novel instrumentation—reinforcing ESA’s role as a global leader in space exploration and innovation.

How to cite: Helbert, J., Haag, M., Bründl, T.-M., Ordoubadian, B., Wittig, S., and Linder, M. and the The L4 Expert Committee and the L4 Payload Working Group: The Mission to Enceladus – The ESA L4 mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2724, https://doi.org/10.5194/egusphere-egu26-2724, 2026.

Assembly and test of the DraGMet Flight Model (FM) hardware for Dragonfly’s July 2028 launch has begun. The Flight Model seismometer was delivered from JAXA in October 2025 and has been integrated with the APL winch assembly and has undergone vibration and other tests. The flight lot of wind sensors have been performance-tested in the Titan Pressure Environment Chamber at APL, and the best-performing units selected as FMs and spares. An opportunity also arose to test the wind sensor design in a heavy gas (1,1,1,2-tetrafluoroethane, R-134a) atmosphere in the Transonic Dynamics Tunnel (TDT) at NASA Langley Research Center during aerodynamic tests on the Dragonfly vehicle. I will review these and other progress highlights of DraGMet which comprises 12 different sensor types with a common DPU to explore the atmosphere, surface and interior of Titan less than 9 years from now.

How to cite: Lorenz, R.: Development of Geophysics and Meteorology Sensors for Titan : Update on Dragonfly’s DraGMet package, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5947, https://doi.org/10.5194/egusphere-egu26-5947, 2026.

Observations from the Cassini mission revealed cryogenic water plumes from the small moon Enceladus are the dominant source of heavy material in Saturn’s magnetosphere. This fascinating insight indicates that a relatively small body dominates the entire giant planet magnetosphere. However, no evidence of magnetospheric impact was observed from Titan, despite this moon being much large with a very dense, unprotected (nitrogen dominated) atmosphere.  Interestingly, more recent data analysis of the entire Cassini dataset indicates Titan can experience previously unknown brief active periods. In particular, global magnetospheric energetic ion composition modifications were observed originating from an abrupt increase in Titan atmospheric loss. We characterize this event and discuss the possible causes as: (1) a methane cycle interruption; (2) an impact event; (3) enhanced surface activity; and/or (4) transiently enhanced solar wind exposure. Our results indicate that such activity can impact the entire magnetosphere and opens up the possibility for similar atmospheric loss events on other bodies.

How to cite: smith, H. and Johnson, R.: Indication of an unusual atmospheric loss event at Titan , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7511, https://doi.org/10.5194/egusphere-egu26-7511, 2026.

Titan’s atmosphere provides a unique laboratory to study how photochemistry, photoionisation, radiative and escape processes shape the atmospheric properties of a nitrogen-rich atmosphere very different from Earth’s. We present a new extension of the 1D first principles upper atmospheric code Kompot, and benchmark it against Titan’s thermosphere. The code self-consistently calculates the thermal and chemical structure of Titan’s upper atmosphere by solving the coupled hydrodynamic, photochemical kinetic, and energy balance equations. The energy balance equation is primarily set by heating due to stellar X-ray and ultraviolet (XUV) and infrared radiation, chemical heating, radiative cooling by methane(CH₄) and hydrogen cyanide (HCN), and thermal conduction. We calculate XUV heating from first principles and do not use any efficiency factor. Our model results are in good agreement with Cassini-Huygens and ALMA observations of Titan. The simulated abundances of the key molecular species, including CH₄, also show strong agreement with Cassini-Huygens results. Molecular hydrogen has the strongest thermal Jeans escape in our model, where as the thermal escape of CH₄ is negligible. Our results suggest that present-day Titan’s CH4 abundance at the upper thermosphere can be explained by a self-consistent model without invoking strong atmospheric escape.

How to cite: Boro Saikia, S., Tennyson, J., Ji, S., Robeling, N.-M., Stanković, I., Van Looveren, G., Schleich, S., Johnstone, C., Kislyakova, K., and Güdel, M.: Self-consistent modelling of Titan's upper atmosphere: energy balance, photochemistry, and Jeans escape, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7633, https://doi.org/10.5194/egusphere-egu26-7633, 2026.

Cassini’s exploration of Enceladus’ plume provided tantalizing glimpses into the chemistry of the moon’s interior ocean. The abundance of H₂ in the plume, for instance, seems to suggest hydrothermal processes operating within Enceladus’ ocean that could support its habitability. But some caution is warranted when drawing conclusions about the ocean composition from the plume, since space weathering can alter plume material as it transits from the source to the spacecraft. We quantitatively evaluate the extent of this modification in terms of the H₂ generated by radiolysis of plume ice grains, using a Monte Carlo model that captures both production and transport. We find that plume photoelectrons are the dominant drivers for radiolysis despite depletion of electron density by nanograin charging. Under nominal conditions, radiolytic H₂ production appears to be insufficient to account for the reported H₂ mixing ratio of ~1%, so the hypothesis of a hydrothermal source still stands. However, we note that our estimates are acutely sensitive to the assumed size distribution of emitted plume grains, which is not well constrained by Cassini observations. We show that, for example, a relatively high power-law exponent of 5 for the grain size distribution, which is consistent with some Cassini-based estimates, makes a radiolytic source for the reported H₂ much more plausible. This demonstrates that further in-situ measurements are needed to support reliable inferences about the Enceladus ocean from observations of the exterior.

How to cite: Grayson, R. W. and Nordheim, T. A.: Exploring Exogenic Sources of Plume H2 at Enceladus, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14572, https://doi.org/10.5194/egusphere-egu26-14572, 2026.

The observation of active jets of ice grain and vapour emanating from four warm faults (called tiger stripes) at Enceladus’s South Pole was one of the major discoveries of the Cassini-Huygens mission (Porco et al. 2006, Spencer et al. 2006, Waite et al. 2006, Spahn et al. 2006).  Infrared mapping carried out by the Visual and Infrared Imaging Spectrometer (VIMS) on board the Cassini spacecraft provided information on surface composition, but also on the physical state (grain size and degree of crystallinity) near active faults (Brown et al. 2006, Jaumann et al., 2008; Taffin et al., 2012; Filacchione et al., 2016, Combes et al. 2018, Robidel et al. 2020). However, many spectral characteristics were not fully exploited by previous studies. Here, by acquiring laboratory infrared spectra of ice powder analogues, we identified several salt compounds, and potentially CO2 clathrate, at the surface, with a higher concentration along active faults. Our analysis shows that the spectral signatures in the inter-stripe regions are consistent with fresh, cold, fine-grained ice deposits, while ice near the tiger stripes has been thermally processed. The higher concentration of salts observed along the tiger stripes, as well as the main spectral features of water ice, imply significant sublimation and sintering processes in the vicinity of active jet sources. These new results provide essential constraints for identifying the best landing site for a future mission to Enceladus and for anticipating the mechanical properties of the icy regolith.

How to cite: Tobie, G., Iglesias-Munoz, V., Scordia, L., Seignovert, B., Le Menn, E., Le Mouélic, S., Modé, N., Artoni, R., Bollengier, O., and Choblet, G.: New constraints on the composition and physical properties of the icy surface on Enceladus’ South Polar Terrain, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19674, https://doi.org/10.5194/egusphere-egu26-19674, 2026.

References:

Palmer, M. Y. et al. ALMA detection and astrobiological potential of vinyl cyanide on Titan. Sci. Adv. 3, e1700022 (2017).

Stevenson, J., Lunine, J. & Clancy, P. Membrane alternatives in worlds without oxygen: Creation of an azotosome. Sci. Adv. 1, e1400067 (2015).

Mayer, C. & Nixon, C. A. A proposed mechanism for the formation of protocell-like structures on Titan. Int. J. Astrobiol. 24, e7 (2025).

Vinatier, S. et al. Study of Titan’s fall southern stratospheric polar cloud composition with Cassini/CIRS: Detection of benzene ice. Icarus310, 89–104 (2018).

Acknowledgement:

Portions of this research were performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration and California Institute of Technology.

How to cite: McQueen, Z., Nixon, C., and Sung, K.: Infrared Search for Vinyl Cyanide in Cassini/CIRS Polar Winter Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22787, https://doi.org/10.5194/egusphere-egu26-22787, 2026.