Orals: Wed, 6 May, 14:00–14:00 | Room 0.94/95
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.
In the near future two space missions will aim to study the Galilean satellites to assess the internal structure of the icy crusts and to detect subglacial liquid water, using radar sounders. To properly interpret the radar data, it is necessary to understand the dielectric properties of the icy shells of these bodies, as they control radar signal penetration and anomaly (i.e., water) detection. The current knowledge of these properties for the types of water ices believed to be present in those moons is limited, which would potentially produce incorrect interpretations of the radar data, thus risking the scientific goals of these missions. Thanks to funded ERC Advanced grant SWIM (Surfing radio waves to detect liquid water in the solar system), we start developing new methodologies and protocols to create a groundbreaking knowledgebase that fills this critical gap. To reach this goal, we started to apply a novel methodology for conducting dielectric measurements across a wide range of frequencies (including the challenging interval used by these radar systems) and temperatures representative of the different ice-forming environments. Such measurements will be integrated with CT microtomography imaging, Raman spectra and molecular dynamic modelling, to address several unresolved questions regarding the dielectric properties of pure and doped ice. Such pioneering research will create a wide-ranging dataset of the dielectric properties of non-terrestrial ices and will allow to obtain the maximum benefit from missions such as JUICE and Europa CLIPPER.
How to cite: Pettinelli, E.: Understanding ice dielectric properties through the SWIM project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18709, https://doi.org/10.5194/egusphere-egu26-18709, 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.
Orals: Thu, 7 May, 14:00–15:40 | Room 0.94/95
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 PO43-) 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.
Titan’s atmosphere is a dense and active chemical reactor forming complex organic and nitrile species relevant to prebiotic chemistry. Molecular nitrogen (N2) and methane (CH4) undergo photolysis and subsequently react to form more complex molecules that then continue this photochemical process creating a vast chemical network leading to the formation of organic hazes that give Titan its characteristic glow. Nitriles in Titan’s atmosphere, specifically, are of astrobiological interest as they make up the necessary precursors to more complex molecules, such as amino acids, necessary for the formation of life. One nitrile species, vinyl cyanide (C2H3CN), previously detected in ALMA (Atacama Large Millimeter Array, Palmer et al. 2018) observations of Titan’s atmosphere bears significant astrobiological relevance. Stevenson et al. (2015) reported that vinyl cyanide had the capability to form self-assembled structures that resembled cell membranes in oxygen poor environments such as Titan. Furthermore, Mayer and Nixon (2025) recently proposed a mechanical mechanism for the formation of vesicles through precipitation induced spray droplets from the surface of Titan’s methane lakes when a thin monolayer of amphiphiles such as vinyl cyanide are present. Here, we present the search for vinyl cyanide in infrared observations of Titan’s south polar limb from Cassini’s Composite InfraRed Spectrometer (CIRS). We make use of a newly obtained pseudo line list from a high-resolution measurement of the vinyl cyanide mid-infrared spectrum. Using this new spectroscopic information, we search for the vibrational mode, centered at 682 cm-1, in CIRS observations from Cassini’s T110 flyby of Titan’s south polar limb (89 S) during the southern polar winter in March of 2015. Vinatier et al. (2018) used these observations previously to detect the infrared spectral signature of benzene ice at 680 cm-1; however, at that time, the infrared spectrum of vinyl cyanide was not well characterized. Even following the inclusion of benzene ice into the spectrum, there is still a significant residual remaining in the CIRS spectrum near 682 cm-1, indicating a missing gas in the radiative transfer model of these observations. With this detection, we can also show how vinyl cyanide is enriched at Titan’s winter pole and assess the astrobiological relevance of this key nitrile species.
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.
Jupiter’s moon Europa is one of the prime targets for planetary exploration due to its high astrobiological potential. Its young surface age, on average between ∼40 – 90 Myr old (Bierhaus et al., 2009) suggests that some form of resurfacing has occurred in the past, with impacts being one of several possible triggering mechanisms. Moreover, impacts onto the ice shell of Europa likely have affected the ice shell dynamics leading to a convective state.
Europa’s ice shell thickness is poorly known with literature values ranging from <1 km (Billings et al., 2005) to 90 km (Villela et al., 2020), with recent studies favoring a range of 23 - 47 km (Howell, 2021). Basin and crater shapes provide important information about the ice shell’s thermal state, thickness, and dynamics (conductive vs. convective). A transition in crater morphology for diameters larger than ∼8 km indicates a weak layer at ~7–8 km depth, as inferred from numerical modelling and observational crater-depth studies (Bray et al., 2014; Schenk, 2002). This layer could potentially represent warm convecting ice or the presence of the liquid ocean (e.g., Silber and Johnson, 2017). A recent study about multiring basins on Europa suggests an ice shell thickness larger than 20 km consisting of a 6-8 km conductive layer overlying a warm convecting region (Wakita et al., 2024).
Here, we investigate how impacts affect the dynamics of Europa’s ice shell using the geodynamic code GAIA (Hüttig et al., 2013). Impact thermal-induced and compositional anomalies are parameterized using scaling laws (Melosh, 1989). We assume that the water produced as a consequence of the impact process rapidly recrystallizes, but leaves behind a chemical and thermal anomaly in the shallow layers of the ice shell. Our models include a composite rheology (Goldsby & Kohlstedt, 2001), pressure- and temperature-dependent thermal expansivity and thermal conductivity (Feistel & Wagner; Wolfenbarger et al., 2021), and the effects of tidal heating (Tobie et al., 2003). We test scenarios with different impactor sizes (0.5 km - 1.8 km), thermal states at the time of the impact (i.e. cold conductive or warm convective ice shell), and ice shell rheology (via changing the grain size). We vary the chemical density anomalies due to impactor material assuming mixtures of ice, salts, and dust. To this end, we consider the presence of salts in concentrations ranging between that of the Earth's ocean and twice as high.
Our models show that impacts can initiate thermal convection in an otherwise conductive ice shell. The material introduced by impacts may remain trapped in the cold conductive upper layer if no surface mobilization occurs. For large impacts, the impactor material can reach the convective ice layer and become mixed into the ice shell, reaching the ice-ocean boundary.
In a future step, we will consider the impact-induced thermal anomalies based on shock physics models instead of scaling laws. We will use the modelled density anomalies associated with thermal and compositional anomalies introduced by impacts to determine their gravity signature that could be potentially detected by Europa Clipper and JUICE.
How to cite: Izzo, D., Plesa, A.-C., Dai, K., Wuennemann, K., and Hussmann, H.: The Effects of Impacts on Europa’s Ice Shell Dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-536, https://doi.org/10.5194/egusphere-egu26-536, 2026.
Investigations of ice-shell flexure, as observed from stereo-derived topographic profiles, have been commonly used to provide information on the interior structure and evolution of icy moons (e.g., Nimmo et al., 2002, Peterson et al., 2015). The most commonly used approach is to fit the observed flexure to an elastic plate model to infer the local elastic thickness of the body’s ice shell at the time of deformation. The widespread use of this approach lies in its quick analytical expression, allowing to test various parameters at multiple locations (e.g., Turcotte & Schubert, 2002). However, it remains unclear whether elastic plate models can be used to reliably predict the flexure of an elastic-plastic ice shell.
For geologic interpretations, the elastic thickness parameter can be converted to a heat flux using several approaches. First, by setting the bending moment of the elastic plate equal to the bending moment of a more realistic plate with a rheology that considers fracturing and viscous flow (e.g., McNutt, 1984). One critical issue during this approach is related to the selection of the input curvature of the plate, which affects the calculation of the bending moment. Alternative approaches have assumed the base of the elastic lithosphere to be defined by a rheology-dependent isotherm in combination with a specific Deborah number (e.g., Nimmo et al., 2002). However, it remains unclear what Deborah number should be assumed when the plate is elasto-plastic and whether both the equal-bending moment and the Deborah number approaches lead to similar results.
In this work, we follow the framework developed in Mueller & Phillips (1995), to test the applicability of elastic plate models to icy satellites. We show that the maximum curvature of the synthetic elastic flexural profile should be used when relating elastic thickness to heat flux and discuss that purely elastic models predict unrealistic oscillations near and in the flexural bulge region. Finally, we reveal that previous work that used the Deborah number approach substantially overestimated the heat flux of Ganymede (Nimmo et al., 2002) and Ariel (Peterson et al., 2015), with implications for the geologic history of these icy worlds.
McNutt, M. K. (1984). Lithospheric flexure and thermal anomalies. J. Geophys. Res.: Solid Earth, 89. doi: 10.1029/jb089ib13p11180.
Mueller, S. and R. J. Phillips (1995). On the reliability of lithospheric constraints derived from models of outer-rise flexure. Geophys. J. Int., 123. doi:10.1111/j.1365- 246x.1995.tb06896.x
Nimmo, F., Pappalardo, R.T., & Giese, B. (2002). Effective elastic thickness and heat flux estimates on Ganymede, Geophys. Res. Lett., 29(7), doi:10.1029/2001GL013976.
Peterson, G., F. Nimmo, and P. M. Schenk (2015). Elastic thickness and heat flux estimates for the Uranian satellite Ariel, Icarus 250, doi: 10.1016/j.icarus.2014.11.007.
Turcotte, D. L. and G. Schubert (2002). Geodynamics. Cambridge University Press. doi: 10.1017/cbo9780511807442.
How to cite: Broquet, A.: Elastic Plastic Flexure on Icy Moons: Implications for heat flux, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6551, https://doi.org/10.5194/egusphere-egu26-6551, 2026.
Icy worlds such as Europa, Enceladus and Ceres show evidence for subsurface liquids reaching the surface, either as plumes or effusive flows. Regions where this has occurred serve as potential archives of subsurface chemistry and habitability, making them prime targets for future missions. Subsurface fluids on these bodies may range in salinity from dilute to eutectic compositions, with brines approaching eutectic concentrations expected to be more common in the shallow subsurface due to their longevity at low temperatures. Despite their importance, little is understood about how highly saline fluids evolve if exposed to surface conditions.
We exposed large quantities (~50 kg) of NaCl and MgSO4 brines at eutectic concentrations to pressures below their triple points and observed their physical behavior and thermal evolution. We found that eutectic brines, if emplaced into low-pressure environments, resist evaporatively driven freezing through the formation of salts at their surface which acts to strongly decrease evaporation rate. Furthermore, instead of evolving towards the eutectic point and thus complete solidification, the salinity and temperature of the brines instead asymptotically approached their hydrate liquidus at a concentration approximately 3% above the eutectic concentration. After 120-300 minutes, both brines approached steady-state whereby salts precipitated at the surface and sank, to be replaced by fresh surficial salts. Our findings indicate that eutectic liquids could be relatively long-lived in low-pressure environments. Furthermore, although emplaced brines at icy worlds may freeze conductively from below, ice formation should not be expected in the upper 10s of cm simulated by these experiments. Instead, we predict the systems should continue to evaporate and precipitate hydrates until dryness, meaning that regions where eutectic brines have been emplaced could be indicated by salt lags rather than salt-bearing ices. Our findings provide a new perspective on surface processes involving the extrusion of high-salinity liquids into low-pressure environments and the possible longevity of liquid water under non-equilibrium scenarios on planetary surfaces.
How to cite: Fox-Powell, M., Broz, P., Patočka, V., Sindhu, P., Hamp, R., Sylvest, M., Emerland, Z., and Patel, M.: Large volumes of eutectic brines resistant to freezing at low pressures: implications for effusive flows on icy worlds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21408, https://doi.org/10.5194/egusphere-egu26-21408, 2026.
Icy moon interiors and terrestrial glacier environments often contain a degree of saltwater melt. This liquid phase can modify the flow of ice, creating preferred directions for deformation through a melt preferred orientation (MPO) that may form in response to stress. Ice crystals adjust on the microscale to drive flow, imparting a crystallographic orientation fabric (COF) that can also be measured to infer the subsurface stress and strain conditions. We show results from laboratory experiments on compressive flow, characterizing the response of both ice crystals and saltwater melt as they together define the geophysical properties of multiphase, partially melted ice. We observe conclusively that an MPO forms parallel to the compressive stress direction, enhancing and possibly tracking material flow, and note that the extent of solid material deformation may decrease with increasing melt fraction. Finally, we combine evolving COF and MPO to define potential radar sounding returns as indicators of subsurface flow, finding that MPO imparts distinct signatures that may be useful in decoding the stress and strain state of icy settings from remote sensing observations.
How to cite: Seltzer, C., Yamauchi, H., Huntsman, C., McCarthy, C., Cross, A., and Hills, B.: Contributions of saline meltwater to ice flow and its remote sensing signatures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7799, https://doi.org/10.5194/egusphere-egu26-7799, 2026.
Europa and Enceladus present two bodies in our Solar System that, besides Earth, contain liquid water and therefore the chance of extraterrestrial life. Regarding the state and evolution of their H2O-layer there are still many open questions. One important mechanism is the heat transport through the outer solid ice shell. It is still unclear whether the ice shells are in a conductive state or if convection takes place. One significant parameter determining if its possible that convection can set in is the ice shell thickness which is unknown for both icy moons. Since both celestial bodies are in the vicinity of enormous planets, namely Jupiter and Saturn, they are subjected to significant tidal forces. These forces can result in additional heating of the ice shell. Due to this further energy source convection might be possible for ice shell thicknesses smaller than predicted by Rayleigh-Bénard convection.
We numerically investigate how an additional uniform internal heating affects the point for the onset of convection in a two-dimensional Cartesian system that is also heated from below. The point for the onset of convection is characterized by the critical Rayleigh number that describes the strength of convection. With an increasing internal heat production rate, the critical Rayleigh number decreases, meaning that less force is required to initiate convection compared to a purely basally heated system. Furthermore, we use these results to derive corresponding minimum ice shell thicknesses. Depending on the viscosity of the ice, we find values between 8 km and 83 km for a system without internal heating that are reduced to 1.5 km to 15 km for the largest investigated heating rate for Europa. For Enceladus, our results yield thicknesses of 22 km to 223 km (no heating) down to 3 km to 30 km (largest heating). Comparing these values to actual estimations of the ice shell thickness for the moons exhibit a realistic chance for Europa’s ice shell to convect but only a small likelihood for Enceladus’ ice shell.
How to cite: Sitte, H. W., Wong, T., Stein, C., and Hansen, U.: Onset of Convection affected by Internal Heating - Implications for Europa and Enceladus, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3442, https://doi.org/10.5194/egusphere-egu26-3442, 2026.
It has been long puzzling whether the ice thickness variations observed on Enceladus can be sustained solely by a polar-amplified bottom heating. The key to this question is to understand how the upward heat transport by convective plumes would be interfered by the temperature and salinity variations beneath the ice due to the ice thickness variations, which however, has yet to be explored. Here, we find that the horizontal temperature variation induced by the ice topography can easily be orders of magnitude greater than the vertical temperature variation induced by bottom heating using scaling analysis. Due to the dominance of horizontal temperature gradient, convective plumes are completely shut off by a stratified layer under the thin ice formed out of baroclinic adjustment, largely slowing down the vertical tracer transport. The stratified layer will also deflect almost all of the core-generated heating toward the regions with thicker ice shell, destroying the ice thickness gradient. These results allow us to put an upper bound on the core-generated heating on Enceladus, which is crucial for the estimate of habitability. Scaling laws for the bottom heat flux to penetrate the stratification is derived and examined. This scaling can be used to constrain the maximum ice thickness variations induced by heterogeneous bottom heating on icy satellites in general, which can be used to differentiate icy satellites that generate the majority of heat in the ice shell from those that generate the majority of heat in the silicate core.
How to cite: Kang, W. and Wang, S.: The modulation effect of ice thickness variations on convection in icy ocean worlds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3571, https://doi.org/10.5194/egusphere-egu26-3571, 2026.
Subsurface oceans hosted by icy bodies in the outer Solar System—such as Europa, Ganymede, Enceladus, Titan, and even dwarf planets like Ceres and Pluto—are prime targets for astrobiological exploration due to their potential to sustain habitable environments. Accordingly, numerous space missions, including JUICE, Europa Clipper, Dragonfly, Dawn, and New Horizons, are designed to investigate the internal structures, thermal states, and chemical environments of these worlds. Recent studies have highlighted the critical role of clathrate hydrates, which exhibit lower thermal conductivity and higher viscosity than water ice, thereby significantly influencing heat transport (convection and conduction), rheological properties, and long-term ocean stability.
Building on the hydrate–ice mixing model (Miller et al., 2025), we aim to systematically incorporate the dynamic integration of clathrate hydrates into a time-dependent thermal evolution framework across a broad parameter space. Our model improvements focus on several key aspects. First, we will consider multiple scenarios for radioactive element abundances, including both long-lived and short-lived radionuclides, and examine how accretion and differentiation time affect internal heating histories. Second, the release and redistribution of methane and other volatile gases are dynamically coupled to core temperature evolution. Third, to extend the model to large icy moons such as Europa, Ganymede, and Titan, we will explicitly include tidal heating and account for high-pressure phases of ice and clathrate hydrates. Fourth, porosity evolution and radius changes are incorporated to explore potential implications for internal structure and surface morphology.
We will first apply the optimized model to Ceres as a benchmark case, exploring how different hydrate–ice mixing states affect its internal structure and the evolution of a potential subsurface ocean. Preliminary expectations suggest that clathrate hydrates may facilitate ocean formation and prolong ocean stability. The refined model will then be applied to Europa, Ganymede, and Titan, where the inclusion of hydrate layers is expected to reduce the energetic requirements for sustaining subsurface oceans, resulting in more physically consistent thermal and structural evolution scenarios.
These results can provide new insights into the chemical and physical controls on the evolution of icy ocean worlds and support the interpretation of forthcoming mission data.
How to cite: zhang, M.: Dynamic Integration of Clathrate Hydrates in the Thermal Evolution of Subsurface Oceans on Icy Moons, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12901, https://doi.org/10.5194/egusphere-egu26-12901, 2026.
Thermal buoyancy is a primary driver of icy-satellite ocean dynamics, caused by mantle heating at the seafloor and cooling at the ice–ocean interface. A significant driver of mantle heating is dissipation by cyclic tidal deformation. When this buoyancy forcing is spatially uniform, laboratory and numerical experiments have shown that it can create overturning circulation, melting and freezing of the overlying ice, and alternating east–west jets of rapid circulation. Tidal dissipation, however, naturally varies in space, causing differential heating of the ocean bottom. These temperature variations will drive horizontal convection, a large-scale overturning circulation with a zonal structure. Here, we investigate the mechanics of this horizontal convection, its interaction with Rayleigh-Bénard (vertical) convection, and dynamic feedback with ice-shell thickness, melting, and freezing.
We perform non-rotating simulations of convection in a 2D Cartesian geometry with a mobile ice–ocean interface using the pseudo-spectral code, Dedalus. A sinusoidal temperature profile is imposed on the bottom of the ocean as well as a vertical (average) temperature difference. The relative amplitude of horizontal to Rayleigh-Bénard convection is varied by changing the ratio of the vertical to horizontal temperature differences, as well as the aspect ratio of the domain. The phase change between pure water and ice is captured using the phase field method. We perform sensitivity tests to determine the optimum phase field parameters that best approximate stagnation-point flow solutions in the vicinity of the ice–ocean interface. These optimum parameters vary as a function of vertical Rayleigh number. We then investigate the competition between Rayleigh-Bénard and horizontal convection without phase change, before including melting and freezing to study the dynamic feedback of ice topology on this competition. Finally, we seek to place our simulations in the context of icy-satellite oceans by determining scaling relationships between the horizontal Rayleigh and Nusselt numbers.
How to cite: Hay, H., Rees Jones, D., Hester, E., and Lemasquerier, D.: Horizontal Convection in Icy Satellite Oceans with Melting and Freezing , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7582, https://doi.org/10.5194/egusphere-egu26-7582, 2026.
Flow laws describe how ice deforms as a function of a number of parameters, such as strain, stress, grain-size, temperature, anisotropy or pressure. They are critical to describe the flow of terrestrial glaciers and the tidal and convective deformation taking place in icy moons.
However, whereas Glen’s law is used in the cryosphere science community, the so-called Goldsby and Kohlstedt flow law is used in the icy moon community.
How different are these two types of law? What are their limitations and domain of applicability?
In this work, we first remind the origin and the assumptions behind these two types of law. We then get back to the physics of the deformation processes of concern, in the case of tidal forcing (very low cumulated strain) or convective deformation (very low stresses) to highlight the limits of applicability of the laws.
Using existing laboratory experiments and field measurements we investigate and help inferring the best law to use and provide some illustrations of the impact on the convective response.
How to cite: Montagnat, M., Llorens, M.-G., Motahari, S., Plesa, A.-C., Sotin, C., and Tobie, G.: Toward an appropriate flow law to model icy moons tidal and convective deformation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10209, https://doi.org/10.5194/egusphere-egu26-10209, 2026.
Europa’s ice shell is thought to overlie a global liquid water ocean, with exchange of heat and momentum across the ice–ocean boundary playing a fundamental role in shaping the shell’s structure and dynamics. Previous studies have shown that heterogeneous ocean circulation and tidal heating can imprint spatially variable heat flux and thus melting and freezing at the ice–ocean interface. However, how the ocean’s thermal state and convective vigour influence the morphology of the ice–ocean interface itself remains poorly understood. Here, we investigate coupled ice–ocean dynamics relevant to Europa in a two-dimensional annulus geometry, with the phase transition between the liquid water ocean and the solid ice layer treated self-consistently through a phase-field approach. Spatially variable temperature anomalies are imposed following Lemasquerier et al. (2023), allowing us to explore the effects of heterogeneous tidal heating under different ocean thermal regimes. We find that colder oceans lead to thicker ice shells and systematically rougher ice–ocean interfaces, characterised by enhanced basal ice topography, which may lead to stronger lateral variability in melting and freezing rates. We also note that as the temperature anomaly between the poles and equator increases, heat transport becomes strongly asymmetric. This results in hemispheric-scale contrasts in ice thickness and the formation of two distinct ice hemispheres separated by a global ocean band confined to low latitudes. These conditions promote the development and persistence of basal roughness on spatial scales comparable to large-scale ice shell heterogeneity. Basal ice roughness and associated thickness variations are expected to strongly influence ice shell dynamics by driving lateral ice flow, promoting ice fabric development, and enhancing lateral stress focusing. On Europa, such mechanically heterogeneous ice shells may play a key role in localising deformation, modulating fracture patterns, and controlling pathways for ocean–ice exchange. Our results highlight the ice–ocean interface morphology as a critical, yet often overlooked, outcome of ice–ocean coupling, with important implications for the evolution and dynamics of Europa’s ice shell.
How to cite: Maas, C., Grima, A. G., and Hansen, U.: Ice–ocean interactions as a driver of basal ice roughness and ice shell evolution on Europa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7604, https://doi.org/10.5194/egusphere-egu26-7604, 2026.
Impact ionisation mass spectrometers, such as the Cosmic Dust Analyser (CDA) onboard Cassini and the SUrface Dust Analyzer (SUDA) onboard Europa Clipper, are key instruments to investigate the composition of icy ocean moons1. They are capable of detecting organics in ice grains ejected from cryovolcanic processes (e.g. Enceladus’ plume) and micrometeoritic bombardment of the icy surface. Laboratory analogue experiments that replicate ice grain impact ionisation mass spectra are crucial in order to reliably identify chemical features of organics in spacecraft data. The laser-induced liquid beam ion desorption (LILBID) technique allows the accurate simulation of impact ionisation mass spectra at a range of impact velocities, by desorbing ionic and neutral molecules and fragments from a μm-sized liquid beam containing water and dissolved analytes2. This work investigates amygdalin (C20H27NO11) and its mass spectral fingerprint with LILBID, aiming to assist in the analysis of organic molecules with impact ionisation mass spectrometry. Upon measurement, amygdalin undergoes protonation-induced chemical transformations (PICTs), enabled by the high laser energy input and proton-rich environment created upon disintegration of the water matrix. The observed reactivity is a distinct phenomenon that can be set apart from other well-characterised processes that analytes can be subject to upon measurement with LILBID and impact ionisation mass spectrometry (e.g. fragmentation). PICTs observed in amygdalin feature its initial nitrile group as well as other functional groups obtained after the first transformation (e.g. carboxylic acid), resulting in multiple reactions products identified by their characteristic molecular ions. Complementary measurements with nuclear magnetic resonance spectroscopy confirmed that reactivity does not occur in solution prior to desorption, and must therefore occur under LILBID measurement. In principle, functional groups similar to nitrile (e.g., amide or ketone) in other compounds could also be subject to PICTs. PICTs may also occur with spaceborne impact ionisation, potentially complicating the identification of organics contained in ice grains. This work builds towards a better understanding of PICTs and their effect(s) on the detection of organic compounds using impact ionisation mass spectrometry, and has key implications for the interpretation of Cassini’s CDA data and for investigations of the composition of icy ocean moons with upcoming space missions (e.g. Europa Clipper or ESA’s large-class mission to Enceladus).
[1] S. Kempf et al., Space Sci. Rev. 221, 10 (2025)
[2] F. Klenner et al., Rapid Comm. Mass Spectrometry 33 (22), 1751–1760 (2019)
How to cite: Hortal Sánchez, L., Napoleoni, M., Brunet, E., Klenner, F., O'Sullivan, T. R., Ackley, M., Danger, G., Abel, B., Khawaja, N., and Postberg, F.: Protonation-induced chemical transformations of complex organics in mass spectrometry: implications for the exploration of icy moons, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3549, https://doi.org/10.5194/egusphere-egu26-3549, 2026.
Saturn’s icy moon Enceladus is the prime target for ESA’s fourth large-class mission (L4) [1]. In addition to placing an orbiter around Enceladus, the mission would involve deploying a lander to the South Polar Terrain of the moon. A crucial parameter to ensure safe landing is the intrusion depth of the lander on Enceladus’ icy surface. In this study, our main goal is to calculate this intrusion depth considering the structure of the ice shell of Enceladus. For this, we use an existing stratification model for granular matter [2,3], where the density of the surface layers increases with depth due to the gravity of Enceladus. We use parameters derived from compression curves of granular ice from laboratory experiments [e.g., 4], such as the turnover pressure and logarithmic transition width from loose to dense packing, as input parameters for the stratification model. Once the stratification of Enceladus’ icy surface is calculated, we predict the intrusion depth of an object (i.e., ESA’s L4 lander) resting on the surface, which compacts the porous, granular ice due to its weight. We will analyze the sensitivity of the calculated intrusion depth on the input parameters and define worst-case scenarios. Moreover, we will consider additional physical processes such as sintering [5] and will discuss next steps involving dynamic compaction.
References:
[1] Helbert et al. (2025) EPSC-DPS2025-1307. [2] Blum et al. (in revision), submitted to A&A. [3] Bürger et al. (2024), JGR: Planets, 129, e2023JE008152. [4] Lorek et al. (2016), A&A 587, A128. [5] Gundlach et al. (2018), MNRAS 479, 5272–5287.
How to cite: Gundlach, B., Aussel, B., Rückriemen-Bez, T., Güttler, C., Blum, J., Atoni, R., Bruendl, T.-M., Gutierrez, F., Haag, M., Hagermann, A., Helbert, J., Johansson, F. L., Ligterink, N., and Tobie, G.: Predicting the intrusion depth of a lander on the surface of Enceladus using a regolith stratification model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22822, https://doi.org/10.5194/egusphere-egu26-22822, 2026.
In search of extraterrestrial life within our Solar System, icy moons emerge as promising candidates. Previous observations of Jupiter’s moon Europa indicate the existence of a global ocean beneath the moon’s icy shell. As there are only rare, weakly constrained plume activities on Europa compared to the Saturnian moon Enceladus, any future mission will have to penetrate the kilometer-thick ice layer in order to investigate the properties and constituents of the water in the ocean below.
Within the TRIPLE project, initiated by the German Space Agency at DLR, an advanced semi-autonomous exploration system for subglacial lakes and ocean environments is developed. The project aims to contribute to future space missions by demonstrating the following integrated system in an analogue terrestrial test. This includes a melting probe for penetrating the ice layer with a launch and recovery system to deploy a miniaturized underwater vehicle for autonomous investigation of the subsurface water reservoir. The integrated science payload is tailored to allow for detecting complex organics and assessing the potential habitability of both the ice and liquid water environments.
The operational capability of the TRIPLE system will be validated in a test campaign in Antarctica’s Dome C region. This area is of great interest due to the existence of subglacial lakes beneath a layer of ice several kilometers thick. Testing in a terrestrial analogue allows to exploit synergies with polar research, including studies of microbial communities in isolated ecosystems, interactions between ice-sheet and subglacial hydrology, and climate developments. As an intermediate step towards Dome C, the upcoming test campaign of TRIPLE is scheduled for the Antarctic Summer Season 2026/27 on the Ekström Shelf Ice near Neumayer-Station III.
In this contribution, we will present the scientific objectives and the current exploration system of this campaign, and provide an outlook on the following Dome C mission. In view of the primary scientific objectives of a future space mission to Jupiter's moon Europa, we will also comment on challenges and potentials regarding transferability of our sensors and engineering solutions to a planetary mission.
How to cite: Do, M., Becker, F., Bhattacharya, D., Funke, O., Gregorek, D., Heinen, D., Kowalski, J., de Vera, J.-P., Waldmann, C., and Wiebusch, C.: TRIPLE Project: From Antarctic Subglacial Lake Exploration to Icy Moon Missions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18896, https://doi.org/10.5194/egusphere-egu26-18896, 2026.
Between 2006 and 2016, the Cassini mission has conducted 13 downlink bistatic radar (BSR) radio science experiments of Titan’s surface. These experiments employ the High-Gain Antenna (HGA) onboard the Cassini spacecraft as transmitter and NASA’s Deep Space Network (DSN) antennas on Earth as receivers to establish a bistatic radio link bouncing off the surface of Titan. The distinct detection of X-band (λ=3.6 cm) returns from some of the observed Titan regions across different latitudes and longitudes allows to constrain surface roughness and near-surface composition based on the investigation of waveforms’ amplitude, frequency and polarization.
Solid terrains probed by Cassini BSR experiments produce heterogeneous reflections ranging from broad and weak returns to narrower and more powerful echoes or a combination of both. This is indicative of different dominant scattering mechanisms. For purely specular returns, RMS slopes and dielectric constant values—connected to near-surface structure and composition—are retrieved using a Gaussian fit applied to echo spectra, as previously done in BSR data analysis. For weaker returns, contaminated or dominated by diffuse scattering, a full scattering-model-informed fitting approach that combines specular and diffuse reflection components is applied to decuple the two contributions and more accurately characterize surface properties.
Herein, we present a progress update on the analysis of BSR experiments from flybys T14, T27, T34 and T124, highlighting regional variations in forward scattering and providing preliminary findings on surface roughness and near-surface dielectric constant of various regions on Titan. When possible, we exploit echo recordings from different, independently calibrated DSN antennas and discuss and compare BSR results with surface properties inferred from both Earth-based and Cassini (monostatic) RADAR observations.
How to cite: Brighi, G., Poggiali, V., Lalich, D., Zannoni, M., Mastrogiuseppe, M., Hayes, A., and Tortora, P.: Cassini Bistatic Radar Experiments on Titan’s Solid Surfaces: Progress Update on Flybys T14, T27, T34 and T124, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18256, https://doi.org/10.5194/egusphere-egu26-18256, 2026.
Introduction: The Cassini RADAR altimeter enabled the first direct bathymetric measurements of an extraterrestrial sea by sounding liquid hydrocarbon bodies on Titan. These observations revealed that Titan’s seas are remarkably transparent at Ku-band frequencies with depths that can reach several hundreds of meters. Measurements of the electromagnetic properties of the liquids further indicated a methane-dominated composition, with minor contributions from ethane and nitrogen [1]. Together, these results provided robust quantitative constraints on Titan’s hydrocarbon inventory and on the dielectric properties of its surface liquids.
More recently, re-analyses of Cassini Synthetic Aperture Radar (SAR) observations using multi-angular scattering models have independently characterized the dielectric and roughness properties of solid terrains in Titan’s north polar region. This study revealed systematic differences between radar-bright and radar-dark surface units, providing new insights into compositional and morphological heterogeneity across Titan’s polar regions [2].
Seafloor–Surface Scattering Comparison and Liquid Loss Tangent Refinement: In this work, we directly compare the radar backscattering properties of Titan’s seafloors, inferred from combined Cassini RADAR altimetry and SAR observations, with those of exposed solid surfaces characterized through multi-angular scattering analyses. This combined approach enables improved isolation of attenuation effects associated with the overlying liquid column, allowing refinement estimates of the liquid loss tangent, and improved constraints on the dielectric properties of the underlying seafloor. Particular emphasis is placed on Ligeia Mare, for which we derive an independent estimate of the liquid loss tangent using SAR data, yielding to a more accurate electromagnetic characterization of Titan’s second-largest hydrocarbon sea.
Figure 1. Synthetic Aperture Radar (SAR) mosaic of Titan’s northern polar region showing the distribution and morphology of liquid-filled basins and channels. Yellow lines highlight the major liquid bodies, Figure adapted from [3].
Acknowledgements: This work was supported by Italian Space Agency (ASI), contract 2025-4-U.0
References:
[1] Mastrogiuseppe, M., Poggiali, V., Hayes, A., Lorenz, R., Lunine, J., Picardi, G., ... & Zebker, H. (2014). The bathymetry of a Titan sea. Geophysical Research Letters, 41(5), 1432-1437.
[2] M. Mastrogiuseppe et al., "Characterization of Titan’s Northern Polar Terrains From Inversion of Cassini RADAR Data," in IEEE Transactions on Geoscience and Remote Sensing, vol. 64, pp. 1-17, 2026, Art no. 4500117, doi: 10.1109/TGRS.2025.3647365.
[3] Mastrogiuseppe, M., Poggiali, V., Hayes, A.G. et al. Deep and methane-rich lakes on Titan. Nat Astron 3, 535–542 (2019). https://doi.org/10.1038/s41550-019-0714-2
How to cite: Mastrogiuseppe, M., Vallecoccia, G., Raguso, M. C., and Durante, D.: Radar Observations of Titan's Hydrocarbon Seas and Lakes: Refining Liquid Composition and Seafloor Properties, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11843, https://doi.org/10.5194/egusphere-egu26-11843, 2026.
