the surface, and the radiolytic and chemical alteration of atmospheric species (Becker et al. 2024 this collection). Surface radiolytic products (e.g., H₂SO₄, O₂, H⁻-O₂, perchlorates, irradiated salts) detected remotely (MISE, Europa-UVS, EIS color) and in situ in sputtered grains (SUDA) and gasses (MASPEX) together with geological mapping and tectonic re-constructions (EIS, REASON) would provide clues to the fluxes of those species to the ocean. Inferences from any plume samples of the compositions of major ions, and data on CO₂/H₂O ratios, would inform about the pH, salinity, and water activity. The importance of salinity for habitability is discussed in detail in Sect. 1.

The abundances of major ions (MISE, SUDA) constrain the ocean's temperature, density, and viscosity, all of which affect fluid dynamics and mass/heat diffusion in the ocean and at the ocean-rock interface. Thermal mapping of the surface (E-THEMIS) and constraints on the icy shell thickness and brine occurrence within the shell (REASON, MISE, EIS, ECM) also contribute to constraints on the oceanic temperature by providing clues to the ocean's salinity and to the temperature at the ice-ocean interface. Magnetometer data that identify the amplitude and phase of electromagnetic induction from saline ocean waters (ECM, PIMS) will constrain our knowledge of the thickness and conductivity of the ocean layer (Kivelson et al. 2000). Knowledge of the ocean's electrical conductivity can, in turn, provide constraints on the ocean's salinity (Hand and Chyba 2007; Vance et al. 2021). Global oceanic circulation might also create magnetic induction signals, but whether such signals can be detectable by the ECM investigation is subject to further modeling (Vance et al. 2021). Similarly, lateral circulation in the ocean might also be constrained from the topography of the ice-ocean interface (REASON, G/RS) (Zhu et al. 2017; Lobo et al. 2021) and/or surface topography data (EIS). Any interpretations of the ice-ocean interface would need to be grounded in an understanding of tidal heating within the ice (REASON, G/RS, E-THEMIS) (Ojakangas and Stevenson 1989).

The combination of measurements and inferences of ice and ocean thicknesses from ECM, REASON, and G/RS observations, together with composition-based data on density, will constrain the pressure profile within the ocean. Using this information, the density profile of the ocean can be further refined based on knowledge of the ocean's composition—the salinity of the ocean determines the temperature at the ice-ocean interface and the compressibility of the ocean as a function of depth. The convective adiabat of the ocean depends on both of these properties (e.g., Vance et al. 2021), and might thus be inferred from Europa Clipper's combined objectives of understanding Europa's composition, geology, and interior. Further, interpretation of ocean circulation would be grounded in understanding the salinity and pressure conditions of European seawater, and whether the anomalous thermal expansion of water affects fluid motion and thermal transport near the ice-ocean interface (Melosh et al. 2004; Kang et al. 2022).

## 3.3 At the Seafloor

In imagining the habitability of Europa's seafloor, the analogy of microbial communities around deep-sea hydrothermal systems on Earth is tempting (e.g., McCollom 1999). Pore fluids could potentially support sub-seafloor microbial ecosystems within the rock, as have been found on Earth (Huber et al. 2006; Edwards et al. 2005). However, the extent and nature of water rock interaction depends on the changing balance of volcanic and chemical alteration of the seafloor. The high pressures at the base of the ocean might squeeze shut pathways in the rock relative to the permeabilities observed at mid-ocean-ridge depths (~2.5 km) in the Earth's ocean (Klimczak et al. 2019). Conversely, cooling of Europa's rock under a shallower gravitational gradient could create porosity to 10 s of km depth (Vance
the surface, and the radiolytic and chemical alteration of atmospheric species (Becker et al. 2024 this collection). Surface radiolytic products (e.g., H₂SO₄, O₂, H₂O₂, perchlorates, irradiated salts) detected remotely (MISE, Europa-UVS, EIS color) and in situ in sputtered grains (SUDA) and gasses (MASPEX) together with geological mapping and tectonic re-constructions (EIS, REASON) would provide clues to the fluxes of those species to the ocean. Inferences from any plume samples of the compositions of major ions, and data on CO₂/H₂O ratios, would inform about the pH, salinity, and water activity. The importance of salinity for habitability is discussed in detail in Sect. 1.

The abundances of major ions (MISE, SUDA) constrain the ocean's temperature, density, and viscosity, all of which affect fluid dynamics and mass/heat diffusion in the ocean and at the ocean-rock interface. Thermal mapping of the surface (E-THEMIS) and constraints on the icy shell thickness and brine occurrence within the shell (REASON, MISE, EIS, ECM) also contribute to constraints on the oceanic temperature by providing clues to the ocean's salinity and to the temperature at the ice-ocean interface. Magnetometer data that identify the amplitude and phase of electromagnetic induction from saline ocean waters (ECM, PIMS) will constrain our knowledge of the thickness and conductivity of the ocean layer (Kivelson et al. 2000). Knowledge of the ocean's electrical conductivity can, in turn, provide constraints on the ocean's salinity (Hand and Chyba 2007; Vance et al. 2021). Global oceanic circulation might also create magnetic induction signals, but whether such signals can be detectable by the ECM investigation is subject to further modeling (Vance et al. 2021). Similarly, lateral circulation in the ocean might also be constrained from the topography of the ice-ocean interface (REASON, G/RS) (Zhu et al. 2017; Lobo et al. 2021) and/or surface topography data (EIS). Any interpretations of the ice-ocean interface would need to be grounded in an understanding of tidal heating within the ice (REASON, G/RS, E-THEMIS) (Ojakangas and Stevenson 1989).

The combination of measurements and inferences of ice and ocean thicknesses from ECM, REASON, and G/RS observations, together with composition-based data on density, will constrain the pressure profile within the ocean. Using this information, the density profile of the ocean can be further refined based on knowledge of the ocean's composition—the salinity of the ocean determines the temperature at the ice-ocean interface and the compressibility of the ocean as a function of depth. The convective adiabat of the ocean depends on both of these properties (e.g., Vance et al. 2021), and might thus be inferred from Europa Clipper's combined objectives of understanding Europa's composition, geology, and interior. Further, interpretation of ocean circulation would be grounded in understanding the salinity and pressure conditions of European seawater, and whether the anomalous thermal expansion of water affects fluid motion and thermal transport near the ice-ocean interface (Melosh et al. 2004; Kang et al. 2022).

## 3.3 At the Seafloor

In imagining the habitability of Europa's seafloor, the analogy of microbial communities around deep-sea hydrothermal systems on Earth is tempting (e.g., McCollom 1999). Pore fluids could potentially support sub-seafloor microbial ecosystems within the rock, as have been found on Earth (Huber et al. 2006; Edwards et al. 2005). However, the extent and nature of water rock interaction depends on the changing balance of volcanic and chemical alteration of the seafloor. The high pressures at the base of the ocean might squeeze shut pathways in the rock relative to the permeabilities observed at mid-ocean-ridge depths (~2.5 km) in the Earth's ocean (Klimczak et al. 2019). Conversely, cooling of Europa's rock under a shallower gravitational gradient could create porosity to 10 s of km depth (Vance
et al. 2007, 2016), and this effect could vary with latitude if tidal heating in the rock is significant (Běhounková et al. 2021). On Earth, fracture-assisted hydrothermal circulation at mid-ocean ridges extends to depths of at least 10 km (or 300 MPa) (e.g., Solomon et al. 2003; de Martin et al. 2007), so hydrothermal circulation is plausible to depths below Europa's seafloor (the seafloor pressure likely doesn't exceed 200 MPa) in excess of 25 km (cf. Sect. 2.5).

Interactions between the ocean and seafloor depend on the geodynamical state of the silicate interior and are thus also key for understanding Europa's habitability (Dombard and Sessa 2019; Běhounková et al. 2021). Fluid circulation through the seafloor and upper mantle, either as high-temperature hydrothermal activity driven by volcanism (Bland and Elder 2022; Lowell and DuBose 2005) or through low-temperature, exothermic hydration of olivine and pyroxene, i.e., serpentinization, could provide energy to sustain metabolism through the production of hydrogen, methane, and other simple organics (e.g., Vance et al. 2007, 2016).

We note that a “cold” or limited-energy evolution of Europa would mean limited fluxes into the ocean in recent epochs of hydrogen-rich materials from either low- or high-temperature hydrothermal activity. If interior temperatures never exceeded the dehydration temperature of serpentine-group minerals (800–1000 K at Europa mantle pressures; e.g., Bose and Navrotsky 1998), then low temperature hydration of rock by serpentinization may have run to completion (Vance et al. 2016). However, the current understanding of Europa’s rocky interior (Becker et al. 2024 this collection; Roberts et al. 2023 this collection; Greeley et al. 2004; Schubert et al. 2009) strongly suggests that it was heated enough in its history, through radiogenic and accretional heating alone (Fig. 12). The sum of heat sources plausibly would have been sufficient to release bound water and thus for renewed serpentinization (retrograde metamorphism) to continue to be an important process as a complement to volcanic activity, possibly to the present day.

The extent and duration of any volcanic activity is also still an open question. Contemporary volcanism from tidal heating could be limited, for example if radiogenic material partitioned into a silicate crust in an earlier episode of heating (Moore and Hussmann 2009), which could limit the ability of the crust to subsequently heat and tidally deform. But a warm silicate interior cannot be excluded based on current knowledge, and could be producing several TW of heat. Běhounková et al. (2021) show that mantle tidal dissipation could be a substantial source of internal heating during periods of enhanced eccentricity. If the crust and upper mantle was heated sufficiently, then chemical alteration of the upper 10 s of km of crust and mantle will affect the ion and volatile speciation of hydrothermal fluids relative to the input fluids from the overlying ocean. This chemical imprint may be present in materials analyzed by the Europa Clipper mission. On Earth, the effect of this alteration depends on the residence time of the fluids in oceanic crust, the temperature, pressure, and the corresponding rates of the water-rock reactions (Fisher and Wheat 2011). These qualities in turn depend on the composition and permeability of the rocks (e.g., Vance et al. 2007; Glein and Waite 2020; Melwani Daswani et al. 2021). The extent of alteration is likely also affected by the composition of the ocean and pore fluids. The pH and salinity of the liquid will affect speciation and dissolution of mantle rock (Zolotov and Shock 2004) as well as the rates of water-rock interaction (Lamadrid et al. 2017).

To constrain the seafloor activity and understand its contribution to habitability, the Europa Clipper science team will need to combine the measurements from all its investigations. In addition to the investigations of the internal thermophysical structure and composition by G/RS, REASON, ECM, and PIMS, sampling of Europa's surface materials could provide clues to the composition of suboceanic rocks and sediments as well as water-solid reactions
et al. 2007, 2016), and this effect could vary with latitude if tidal heating in the rock is significant (Běhounková et al. 2021). On Earth, fracture-assisted hydrothermal circulation at mid-ocean ridges extends to depths of at least 10 km (or 300 MPa) (e.g., Solomon et al. 2003; de Martin et al. 2007), so hydrothermal circulation is plausible to depths below Europa's seafloor (the seafloor pressure likely doesn't exceed 200 MPa) in excess of 25 km (cf. Sect. 2.5).

Interactions between the ocean and seafloor depend on the geodynamical state of the silicate interior and are thus also key for understanding Europa's habitability (Dombard and Sessa 2019; Běhounková et al. 2021). Fluid circulation through the seafloor and upper mantle, either as high-temperature hydrothermal activity driven by volcanism (Bland and Elder 2022; Lowell and DuBose 2005) or through low-temperature, exothermic hydration of olivine and pyroxene, i.e., serpentinization, could provide energy to sustain metabolism through the production of hydrogen, methane, and other simple organics (e.g., Vance et al. 2007, 2016).

We note that a “cold” or limited-energy evolution of Europa would mean limited fluxes into the ocean in recent epochs of hydrogen-rich materials from either low- or high-temperature hydrothermal activity. If interior temperatures never exceeded the dehydration temperature of serpentine-group minerals (800–1000 K at Europa mantle pressures; e.g., Bose and Navrotsky 1998), then low temperature hydration of rock by serpentinization may have run to completion (Vance et al. 2016). However, the current understanding of Europa’s rocky interior (Becker et al. 2024 this collection; Roberts et al. 2023 this collection; Greeley et al. 2004; Schubert et al. 2009) strongly suggests that it was heated enough in its history, through radiogenic and accretional heating alone (Fig. 12). The sum of heat sources plausibly would have been sufficient to release bound water and thus for renewed serpentinization (retrograde metamorphism) to continue to be an important process as a complement to volcanic activity, possibly to the present day.

The extent and duration of any volcanic activity is also still an open question. Contemporary volcanism from tidal heating could be limited, for example if radiogenic material partitioned into a silicate crust in an earlier episode of heating (Moore and Hussmann 2009), which could limit the ability of the crust to subsequently heat and tidally deform. But a warm silicate interior cannot be excluded based on current knowledge, and could be producing several TW of heat. Běhounková et al. (2021) show that mantle tidal dissipation could be a substantial source of internal heating during periods of enhanced eccentricity. If the crust and upper mantle was heated sufficiently, then chemical alteration of the upper 10 s of km of crust and mantle will affect the ion and volatile speciation of hydrothermal fluids relative to the input fluids from the overlying ocean. This chemical imprint may be present in materials analyzed by the Europa Clipper mission. On Earth, the effect of this alteration depends on the residence time of the fluids in oceanic crust, the temperature, pressure, and the corresponding rates of the water-rock reactions (Fisher and Wheat 2011). These qualities in turn depend on the composition and permeability of the rocks (e.g., Vance et al. 2007; Glein and Waite 2020; Melwani Daswani et al. 2021). The extent of alteration is likely also affected by the composition of the ocean and pore fluids. The pH and salinity of the liquid will affect speciation and dissolution of mantle rock (Zolotov and Shock 2004) as well as the rates of water-rock interaction (Lamadrid et al. 2017).

To constrain the seafloor activity and understand its contribution to habitability, the Europa Clipper science team will need to combine the measurements from all its investigations. In addition to the investigations of the internal thermophysical structure and composition by G/RS, REASON, ECM, and PIMS, sampling of Europa's surface materials could provide clues to the composition of suboceanic rocks and sediments as well as water-solid reactions
<figure><img src="image_13.png" /><figcaption>**Fig. 12 Top:** Bulk accretion temperatures vs object radius, after McKinnon and Zolensky (2003). For a retention factor of *h* = 0.4 (which depends on accretion rate and planetesimal size), Europa's temperature exceeds the dehydration temperature of serpentine minerals (800 K). **Bottom:** Predicted mantle temperatures in Europa at 2.1 and 4.2 Gyr after accretion, including tides. From Běhounková et al. (2021). Adopted with permission from John Wiley and Sons; blue: minimum, red: maximum, black: average, green: solidus temperature)</figcaption></figure>

at the ocean floor. Sampling ⁴⁰Ar and ⁴He (MASPEX) would constrain the rock types, intensity of water-rock interactions, and the extent of radioactive decay of K, U, and Th that affects radiolysis of water and its possible impact on the redox state of oceanic water (e.g., Bouquet et al. 2017). Detecting sulfates, organic compounds, and H₂ could suggest available energy sources for sulfate-reducing organisms, while detecting H₂ together with inorganic C species (carbonates, CO₂) could indicate an energy source for methanogens (McCollom 1999; Zolotov and Shock 2004; Barge and White 2017) or methanotrophs (White et al. 2020). Some of these volatile species (e.g., CO₂, CH₄, NH₃, H₂) of seafloor/oceanic origin could be trapped in the ice shell and some be incorporated, and even brought to the surface, as clathrates (Hand et al. 2007; Bouquet et al. 2019). Europa Clipper can assess the inventory of ice bound clathrates through combined composition investigations of surface
<figure><img src="image_13.png" /><figcaption>**Fig. 12 Top:** Bulk accretion temperatures vs object radius, after McKinnon and Zolensky (2003). For a retention factor of *h* = 0.4 (which depends on accretion rate and planetesimal size), Europa's temperature exceeds the dehydration temperature of serpentine minerals (800 K). **Bottom:** Predicted mantle temperatures in Europa at 2.1 and 4.2 Gyr after accretion, including tides. From Běhounková et al. (2021). Adopted with permission from John Wiley and Sons; blue: minimum, red: maximum, black: average, green: solidus temperature)</figcaption></figure>

at the ocean floor. Sampling ⁴⁰Ar and ⁴He (MASPEX) would constrain the rock types, intensity of water-rock interactions, and the extent of radioactive decay of K, U, and Th that affects radiolysis of water and its possible impact on the redox state of oceanic water (e.g., Bouquet et al. 2017). Detecting sulfates, organic compounds, and H₂ could suggest available energy sources for sulfate-reducing organisms, while detecting H₂ together with inorganic C species (carbonates, CO₂) could indicate an energy source for methanogens (McCollom 1999; Zolotov and Shock 2004; Barge and White 2017) or methanotrophs (White et al. 2020). Some of these volatile species (e.g., CO₂, CH₄, NH₃, H₂) of seafloor/oceanic origin could be trapped in the ice shell and some be incorporated, and even brought to the surface, as clathrates (Hand et al. 2007; Bouquet et al. 2019). Europa Clipper can assess the inventory of ice bound clathrates through combined composition investigations of surface
and any plume materials (MISE, Europa-UVS, SUDA, MASPEX), coupled with geological investigations (EIS, MISE, E-THEMIS, REASON) to assess any influence of clathrates on the mechanical properties of the ice.

# 4 Europa Clipper as a Precursor for a Future Landed Mission

While the search for life will likely require access to Europa's subsurface, a lander or similar in situ mission will be the next logical step in the exploration of this ocean world (Phillips et al. 2021). A landed mission could provide ground-truth for Europa Clipper's remote sensing observations, as well as detailed measurements to address key questions relating to the physical and chemical processes that have shaped Europa through time, its present-day state, the ability to host current or past habitable environments, and the potential for the emergence of life on Europa. Irrespective of whether the next mission to Europa follows the Europa Lander mission concept framework of Hand et al. (2022), a landed mission to Europa will benefit enormously from the data collected by Europa Clipper (Hand et al. 2020). In particular, the collection of reconnaissance data will be important for identifying potential landing sites that satisfy criteria for both science value (e.g., show evidence of recent activity and materials sourced from the subsurface for interrogations of biosignatures and habitability) and where it is safe to land with extant technologies (Sect. 5 of Daubar et al. 2024 this collection; Phillips et al. 2021).

The careful design of the Europa Clipper spacecraft and science operations enables observations of the surface concurrently and/or for overlapping spatial regions and associated atmospheric and space environments. Therefore, measurements by the remote sensing investigations at high resolutions can be correlated with those by the in situ investigations, providing a full picture of the potential for scientific discovery, as well as mapping for terrain relative navigation and the presence or lack of hazards in different regions for a landed mission. Of particular interest for the terrain relative navigation are the stereo visual images that will be obtained by EIS WAC (≤22 m pixel scale) for solar incidence angles between 30 and 60 degrees over at least 40, 2 km × 4 km-sized regions. EIS NAC data will provide information on surface hazards larger than 2–3 m diameter. A potential extended Clipper mission would also provide opportunities for targeted, follow-on observations to further advance science value and landing safety assessments of potential landing sites, and re-observe discoveries from the prime mission that could add potential landing sites. Furthermore, because a landed mission would provide ground-truth for Europa Clipper's gamut of remote sensing observations, these could then be used more confidently for reconnaissance on future orbiter missions.

Europa Clipper will be the first NASA mission to follow the ocean world exploration pathway outlined in the NASA Roadmap to Ocean Worlds (Hendrix et al. 2019), while also addressing the many ocean-worlds objectives in the 2023–2032 Planetary Science and Astrobiology Decadal Survey (National Academies 2022). The roadmap notes that Europa Clipper will close the remaining gaps related to understanding the energy balance of the moon and whether it possessed the physio-chemical conditions for life, paving the way for in situ exploration by a landed mission (Phillips et al. 2021). The NASA Astrobiology Program's Research Coordination Network for Ocean Worlds similarly proposes that a surface landed mission is the next compelling step in exploring this ocean world, emphasizing the key habitability and contextual science that such a mission might return (Howell and Pappalardo 2020). Additionally, Europa Clipper and potential follow-on missions feed forward into future studies of the comparative planetology of other ocean worlds such as Titan,
and any plume materials (MISE, Europa-UVS, SUDA, MASPEX), coupled with geological investigations (EIS, MISE, E-THEMIS, REASON) to assess any influence of clathrates on the mechanical properties of the ice.

# 4 Europa Clipper as a Precursor for a Future Landed Mission

While the search for life will likely require access to Europa's subsurface, a lander or similar in situ mission will be the next logical step in the exploration of this ocean world (Phillips et al. 2021). A landed mission could provide ground-truth for Europa Clipper's remote sensing observations, as well as detailed measurements to address key questions relating to the physical and chemical processes that have shaped Europa through time, its present-day state, the ability to host current or past habitable environments, and the potential for the emergence of life on Europa. Irrespective of whether the next mission to Europa follows the Europa Lander mission concept framework of Hand et al. (2022), a landed mission to Europa will benefit enormously from the data collected by Europa Clipper (Hand et al. 2020). In particular, the collection of reconnaissance data will be important for identifying potential landing sites that satisfy criteria for both science value (e.g., show evidence of recent activity and materials sourced from the subsurface for interrogations of biosignatures and habitability) and where it is safe to land with extant technologies (Sect. 5 of Daubar et al. 2024 this collection; Phillips et al. 2021).

The careful design of the Europa Clipper spacecraft and science operations enables observations of the surface concurrently and/or for overlapping spatial regions and associated atmospheric and space environments. Therefore, measurements by the remote sensing investigations at high resolutions can be correlated with those by the in situ investigations, providing a full picture of the potential for scientific discovery, as well as mapping for terrain relative navigation and the presence or lack of hazards in different regions for a landed mission. Of particular interest for the terrain relative navigation are the stereo visual images that will be obtained by EIS WAC (≤22 m pixel scale) for solar incidence angles between 30 and 60 degrees over at least 40, 2 km × 4 km-sized regions. EIS NAC data will provide information on surface hazards larger than 2–3 m diameter. A potential extended Clipper mission would also provide opportunities for targeted, follow-on observations to further advance science value and landing safety assessments of potential landing sites, and re-observe discoveries from the prime mission that could add potential landing sites. Furthermore, because a landed mission would provide ground-truth for Europa Clipper's gamut of remote sensing observations, these could then be used more confidently for reconnaissance on future orbiter missions.

Europa Clipper will be the first NASA mission to follow the ocean world exploration pathway outlined in the NASA Roadmap to Ocean Worlds (Hendrix et al. 2019), while also addressing the many ocean-worlds objectives in the 2023–2032 Planetary Science and Astrobiology Decadal Survey (National Academies 2022). The roadmap notes that Europa Clipper will close the remaining gaps related to understanding the energy balance of the moon and whether it possessed the physio-chemical conditions for life, paving the way for in situ exploration by a landed mission (Phillips et al. 2021). The NASA Astrobiology Program's Research Coordination Network for Ocean Worlds similarly proposes that a surface landed mission is the next compelling step in exploring this ocean world, emphasizing the key habitability and contextual science that such a mission might return (Howell and Pappalardo 2020). Additionally, Europa Clipper and potential follow-on missions feed forward into future studies of the comparative planetology of other ocean worlds such as Titan,
Enceladus, and possibly Triton, to help us understand what factors lead to the diversity of planetary bodies we see today. Following Europa Clipper's overarching goal, what we learn at Europa will aid in constraining which other confirmed and potential ocean worlds are most likely to host current habitable (if not inhabited) environments.

**5 Conclusion**

NASA's Europa Clipper mission is the first mission designed to investigate the habitability of an icy world, building on lessons from previous missions exploring the outer Solar System. Europa's ocean, ice shell, geology, composition, space environment, recent activity, and astrobiological potential are all linked. Assessing whether Europa harbors the conditions conducive for life is a huge scientific endeavor involving the synthesis of a multitude of measurements and cooperation among a team of experts spanning many scientific disciplines. The Europa Clipper mission will assess Europa's habitability through measurements by the suite of investigations to achieve three primary science objectives involving its ice shell, composition, and geology, and will also investigate the cross-cutting science related to current activity, radiation, geodesy, and sites of high science interest for a future lander. The specific science objectives of the mission are to: (1) characterize Europa's ice shell, ocean, and any subsurface water, including heterogeneity, ocean properties, and the nature of surface-ice-ocean exchange; (2) understand Europa's composition and chemistry; and (3) understand the formation of surface features and characterize localities of high science-interest. The mission will also search for evidence of recent or current activity, notably plumes and thermal anomalies, and characterize these if present. Europa Clipper will also perform geodetic and radiation measurements, and will assess high-resolution, co-located observations at sites. Habitability assessments will overarch these objectives, drawing from all the investigations, as outlined in Table 1. With simultaneous collection of data coupled with models of Europa's ocean, chemistry, evolution, and space environment Europa Clipper will perform an integrated assessment of Europa's habitability. The mission will also gain a further understanding on the tidal energy available and where it is distributed in Europa, if Europa's environment supplies chemical compounds suitable for sustaining life, and what drivers exist (chemical or physical factors, energetic particles, etc.) for providing chemical disequilibria. The habitability of Europa over time will also be considered through knowledge gained from the Europa Clipper mission. The entirety of Europa, its ice-shell, ocean, seafloor, and their interfaces, will be surveyed with the suite of complementary instrument investigations on the Europa Clipper mission to assess their potential as habitable environments.

Jupiter orbit insertion for Europa Clipper is anticipated in 2030. Work continues toward achieving the best integrated Europa scientific models to assess the habitability of this remarkable moon, and to begin the next exciting phase of ocean world exploration.

**Acknowledgements** A part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). © 2023. All rights reserved.

**Funding** FP acknowledges the support by a European Research Council (ERC) Consolidator Grant 724908-Habitat OASIS. JL acknowledges the support of NASA Grant #80NSSC19K1544. JS's research was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities under contract with NASA.MAS acknowledges support from The Science and Technology Facilities Council grant ST/S000615/1 and The Leverhulme Trust grant RPG-2018-012. This work was supported by NASA through the Europa Clipper Project.
Enceladus, and possibly Triton, to help us understand what factors lead to the diversity of planetary bodies we see today. Following Europa Clipper's overarching goal, what we learn at Europa will aid in constraining which other confirmed and potential ocean worlds are most likely to host current habitable (if not inhabited) environments.

**5 Conclusion**

NASA's Europa Clipper mission is the first mission designed to investigate the habitability of an icy world, building on lessons from previous missions exploring the outer Solar System. Europa's ocean, ice shell, geology, composition, space environment, recent activity, and astrobiological potential are all linked. Assessing whether Europa harbors the conditions conducive for life is a huge scientific endeavor involving the synthesis of a multitude of measurements and cooperation among a team of experts spanning many scientific disciplines. The Europa Clipper mission will assess Europa's habitability through measurements by the suite of investigations to achieve three primary science objectives involving its ice shell, composition, and geology, and will also investigate the cross-cutting science related to current activity, radiation, geodesy, and sites of high science interest for a future lander. The specific science objectives of the mission are to: (1) characterize Europa's ice shell, ocean, and any subsurface water, including heterogeneity, ocean properties, and the nature of surface-ice-ocean exchange; (2) understand Europa's composition and chemistry; and (3) understand the formation of surface features and characterize localities of high science-interest. The mission will also search for evidence of recent or current activity, notably plumes and thermal anomalies, and characterize these if present. Europa Clipper will also perform geodetic and radiation measurements, and will assess high-resolution, co-located observations at sites. Habitability assessments will overarch these objectives, drawing from all the investigations, as outlined in Table 1. With simultaneous collection of data coupled with models of Europa's ocean, chemistry, evolution, and space environment Europa Clipper will perform an integrated assessment of Europa's habitability. The mission will also gain a further understanding on the tidal energy available and where it is distributed in Europa, if Europa's environment supplies chemical compounds suitable for sustaining life, and what drivers exist (chemical or physical factors, energetic particles, etc.) for providing chemical disequilibria. The habitability of Europa over time will also be considered through knowledge gained from the Europa Clipper mission. The entirety of Europa, its ice-shell, ocean, seafloor, and their interfaces, will be surveyed with the suite of complementary instrument investigations on the Europa Clipper mission to assess their potential as habitable environments.

Jupiter orbit insertion for Europa Clipper is anticipated in 2030. Work continues toward achieving the best integrated Europa scientific models to assess the habitability of this remarkable moon, and to begin the next exciting phase of ocean world exploration.

**Acknowledgements** A part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). © 2023. All rights reserved.

**Funding** FP acknowledges the support by a European Research Council (ERC) Consolidator Grant 724908-Habitat OASIS. JL acknowledges the support of NASA Grant #80NSSC19K1544. JS's research was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities under contract with NASA.MAS acknowledges support from The Science and Technology Facilities Council grant ST/S000615/1 and The Leverhulme Trust grant RPG-2018-012. This work was supported by NASA through the Europa Clipper Project.
## Declarations

**Competing Interests** The authors have no competing interests to declare that are relevant to the content of this article.

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Arrigo KR (2014) Sea ice ecosystems. Annu Rev Mar Sci 6:439–467. https://doi.org/10.1146/annurev-marine-010213-135103

Arrigo KR, Dieckmann G, Gosselin M, Robinson DH, Fritsen CH, Sullivan CW (1995) High resolution study of the platelet ice ecosystem in McMurdo Sound, Antarctica: biomass, nutrient, and production profiles within a dense microalgal bloom. Mar Ecol Prog Ser 127:255–268. https://doi.org/10.3354/meps127255

Atreya SK, Mahaffy PR, Wong AS (2007) Methane and related trace species on Mars: origin, loss, implications for life, and habitability. Planet Space Sci 55(3):358–369. https://doi.org/10.1016/j.pss.2006.02.005

Ayliffe BA, Bate MR (2009) Circumplanetary disc properties obtained from radiation hydrodynamical simulations of gas accretion by protoplanets. Mon Not R Astron Soc 397:657–665. https://doi.org/10.1111/j.1365-2966.2009.15002.x

Baland RM, Yseboodt M, Van Hoolst T (2012) Obliquity of the Galilean satellites: the influence of a global internal liquid layer. Icarus 220:435–448. https://doi.org/10.1016/j.icarus.2012.05.020

Barge LM, White LM (2017) Experimentally testing hydrothermal vent origin of life on Enceladus and other icy/ocean worlds. Astrobiology 17(9):820–833. https://doi.org/10.1089/ast.2016.1633

Barr AC, Showman AP (2009) Heat transfer in Europa’s icy shell. In: Pappalardo RT et al (eds) Europa. University of Arizona Press, Tucson, pp 405–430

Batygin K, Morbidelli A (2020) Formation of giant planet satellites. Astrophys J 894:143. https://doi.org/10.3847/1538-4357/ab8937

Becker T et al (2024) Exploring the composition of Europa with the upcoming Europa Clipper mission. Space Sci Rev 220

Běhounková M, Tobie G, Choblet G, Kervazo M, Melwani Daswani M, Dumoulin C, Vance SD (2021) Tidally induced magmatic pulses on the oceanic floor of Jupiter’s moon Europa. Geophys Res Lett 48(3):e2020GL090077. https://doi.org/10.1029/2020gl090077

Bierhaus EB, Zahnle K, Chapman CR (2009) Europa’s crater distributions and surface ages. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. University of Arizona Press, Tucson, pp 161–180

Bierson CJ, Nimmo F (2020) Explaining the Galilean satellites’ density gradient by hydrodynamic escape. Astrophys J 897:L43. https://doi.org/10.3847/2041-8213/aba11a

Bland M, Elder C (2022) Silicate volcanism on Europa’s seafloor: implications for habitability. Geophys Res Lett 49:e2021GL096939. https://doi.org/10.1029/2021GL096939

Blankenship DD et al (2024) Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON). Space Sci Rev 220

Blättler CL, Kump LR, Fischer WW, Paris G, Kasbohm JJ, Higgins JA (2017) Constraints on ocean carbonate chemistry and $PCO_2$ in the Archaean and Palaeoproterozoic. Nat Geosci 10(1):41–45. https://doi.org/10.1038/ngeo2844
## Declarations

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Cox R, Bauer AW (2015) Impact breaching of Europa's ice: constraints from numerical modeling. J Geophys Res, Planets 120(10):1708–1719. https://doi.org/10.1002/2015je004877

Craft KL, Patterson GW, Lowell RP, Germanovich L (2016) Fracturing and flow: investigations on the formation of shallow water sills on Europa. Icarus 274:297–313. https://doi.org/10.1016/j.icarus.2016.01.023

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Bonales LJ, Muñoz-Iglesias V, Prieto-Ballesteros O (2013) Raman spectroscopy as a tool to study the solubility of CO₂ in magnesium sulphate brines: application to the fluids of Europa's cryomagmatic reservoirs. Eur J Mineral 25:735–743. https://doi.org/10.1127/0935-1221/2013/0025-2312

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Bouquet A, Glein CR, Wyrick D, Waite JH (2017) Alternative energy: production of H₂ by radiolysis of water in the rocky cores of icy bodies. Astrophys J 840(1):L8. https://doi.org/10.3847/2041-8213/aa6d56

Bouquet A, Mousis O, Glein CR, Danger G, Waite JH (2019) The role of clathrate formation in Europa's ocean composition. Astrophys J 885(1):14. https://doi.org/10.3847/1538-4357/ab40b0

Brockwell TG, Meech KJ, Pickens K, Waite JH, Miller G, Roberts J, Lunine JI, Wilson P IV (2016) The mass spectrometer for planetary exploration (MASPEX). In: 2016 IEEE aerospace conference, Big Sky, MT, USA, 2016, pp 1–17. https://doi.org/10.1109/AERO.2016.7500777

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Catling DC, Kasting JF (2017) Atmospheric evolution on inhabited and lifeless worlds. Cambridge University Press, Cambridge, p 579

Chivers CJ, Buffo JJ, Schmidt BE (2021) Thermal and chemical evolution of small, shallow water bodies in Europa's ice shell. J Geophys Res, Planets 126:e2020JE006692. https://doi.org/10.1029/2020JE006692

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Desch SJ, Kalyaan A, Alexander CM (2018) The effect of Jupiter's formation on the distribution of refractory elements and inclusions in meteorites. Astrophys J Suppl Ser 238(26):11. https://doi.org/10.3847/1538-4365/aad95f

Dietrich LE, Tice MM, Newman DK (2006) The co-evolution of life and Earth. Curr Biol 16(11):R395–R400. https://doi.org/10.1016/j.cub.2006.05.017

Dirkx D, Gurvits LI, Lainey V, Lari G, Milani A, Cimò G, Bocanegra-Bahamon TM, Visser PNAM (2017) On the contribution of PRIDE-JUICE to Jovian system ephemerides. Planet Space Sci 147:14–27. https://doi.org/10.1016/j.pss.2017.09.004

Doggett T, Greeley R, Figueredo P, Tanaka K (2009) Geologic stratigraphy and evolution of Europa's surface. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. University of Arizona Press, Tucson, p 137

Dombard AJ, Sessa AM (2019) Gravity measurements are key in addressing the habitability of a subsurface ocean in Jupiter's moon Europa. Icarus 325:31–38. https://doi.org/10.1016/j.icarus.2019.02.025

Edwards PN (2011) History of climate modeling. WIREs Clim Change 2(1):128–139. https://doi.org/10.1002/wcc.95

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Salter TL, Magee BA, Waite JH Sephton MA (2022b) Mass spectrometric fingerprints of bacteria and archaea for life detection on icy moons. *Astrobiology* 22(2):143–157. https://doi.org/10.1089/ast.2020.2394

Salter TL, Watson JS, Waite JH, Sephton MA (2022a) Hydrothermal processing of microorganisms: mass spectral signals of degraded biosignatures for life detection on icy moons. ACS Earth Space Chem 6(10):2508–2518. https://doi.org/10.1021/acsearthspacechem.2c00213

Sarmiento J, Toggweiler J (1984) A new model for the role of the oceans in determining atmospheric *P* CO₂. Nature 308:621–624. https://doi.org/10.1038/308621a0

Schmidt BE, Blankenship DD, Patterson GW, Schenk PM (2011) Active formation of chaos terrain over shallow subsurface water on Europa. Nature 479:502–505. https://doi.org/10.1038/nature10608

Schubert G, Sohl F, Hussmann H (2009) Interior of Europa. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. Europa University of Arizona Press, Tucson, pp 353–367

Schulik M, Johansen A, Bitsch B, Lega E, Lambrechts M (2020) On the structure and mass delivery towards circumplanetary discs. *Astron Astrophys* 642:A187. https://doi.org/10.1051/0004-6361/202037556

Schulze-Makuch D, Irwin LN (2018) Life and the need for a solvent. In: Life in the universe. Springer, Cham, pp 123–147. https://doi.org/10.1007/978-3-319-97658-7_7

Scott ERD, Krot AN, Sanders IS (2018) Isotopic dichotomy among meteorites and its bearing on the protoplanetary disk. *Astrophys J* 854:164. https://doi.org/10.3847/1538-4357/aaa5a5

Sephton MA, Waite JH, Brockwell TG (2018) How to detect life on icy moons. *Astrobiology* 18:843–855. https://doi.org/10.1089/ast.2017.1656

Shock EL (1988) Organic acid metastability in sedimentary basins. *Geology* 16(10):886–890. https://doi.org/10.1130/0091-7613(1988)016<0886:OAMISB>2.3.CO;2

Shock EL (1989) Corrections to “Organic acid metastability in sedimentary basins”. *Geology* 17:572–573. https://doi.org/10.1130/0091-7613(1989)017<0572:CTOAMI>2.3.CO;2

Shock EL (1994) Application of thermodynamic calculations to geochemical processes involving organic acids. In: Lewan M, Pittman E (eds) The role of organic acids in geological processes. Springer, Berlin, pp 270–318. https://doi.org/10.1007/978-3-642-78356-2_10

Shock EL, Holland ME (2007) Quantitative habitability. *Astrobiology* 7:839–851. https://doi.org/10.1089/ast.2007.0137

Shock EL, Canovas P, Yang Z, Boyer G, Johnson K, Robinson K, Fecteau K, Windman T, Cox A (2013) Thermodynamics of organic transformations in hydrothermal fluids. *Rev Mineral Geochem* 76:311–350. https://doi.org/10.2138/rmg.2013.76.9

Shock E, Bockisch C, Estrada C, Fecteau K, Gould I, Hartnett H, Johnson K, Robinson K, Shipp J, Williams L (2019) Earth as organic chemist. In: Orcutt B, Daniel I, Dasgupta R (eds) Deep carbon, past to present. Cambridge University Press, Cambridge, pp 415–446

Singer KN, McKinnon WB, Schenk PM (2021) Pits, uplifts and small chaos features on Europa: morphologic and morphometric evidence for intrusive upwelling and lower limits to ice shell thickness. *Icarus* 364:114465. https://doi.org/10.1016/j.icarus.2021.114465

Smith HB, Drew A, Malloy JF, Walker SI (2021) Seeding biochemistry on other worlds: Enceladus as a case study. *Astrobiology* 21:177–190. https://doi.org/10.1089/ast.2019.2197

Soderlund KM (2019) Ocean dynamics of outer solar system satellites. *Geophys Res Lett* 46(15):8700–8710. https://doi.org/10.1029/2018GL081880

Soderlund KM, Schmidt BE, Wicht J, Blankenship DD (2014) Ocean-driven heating of Europa’s icy shell at low latitudes. *Nat Geosci* 7(1):16–19. https://doi.org/10.1038/ngeo2021

Soderlund KM, Kalousová K, Buffo JJ, Glein CR, Goodman JC, Mitri G et al (2020) Ice-ocean exchange processes in the Jovian and Saturnian satellites. *Space Sci Rev* 216(5):1–57. https://doi.org/10.1007/s11214-020-00706-6

Solomon SC, Aharonov O, Banerdt WB, Dombard AJ, Frey HV, Golombek MP, Hauck SA, Head JW, Johnson CL, McGovern PJ, Phillips RJ, Smith DE, Zuber MT (2003) Why are there so few magnetic anomalies in Martian lowlands and basins? *Lunar Planet Sci Conf XXXIII. Abstract 1382*

Sotin C, Tobie G (2004) Internal structure and dynamics of the large icy satellites. *C R Phys* 5(7):769–780. https://doi.org/10.1016/j.crp h.2004.08.001

Sotin C, Head JW III, Tobie G (2002) Europa: tidal heating of upwelling thermal plumes and the origin of lenticulae and chaos melting. *Geophys Res Lett* 29:1233. https://doi.org/10.1029/2001GL013844

Sotin C, Tobie G, Wahr J, McKinnon WB (2009) Tides and tidal heating on Europa. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. University of Arizona Press, Tucson, pp 85–117

Sparks WB, Schmidt BE, McGrath MA, Hand KP, Spencer JR, Cracraft M, Deustua SE (2017) Active cryovolcanism on Europa? *Astrophys J* 839:L18. https://doi.org/10.3847/2041-8213/aa67f8

Squyres SW, Reynolds RT, Cassen PM, Peale SJ (1983) Liquid water and active resurfacing on Europa. *Nature* 301:225–226. https://doi.org/10.1038/301225a0

Steinbrugge G, Voigt JRC, Wolfenbarger NS, Hamilton CW, Soderlund KM, Young DA, Blankenship DD, Vance SD, Schroeder DM (2020) Brine migration and impact-induced cryovolcanism on Europa. *Geo-phys Res Lett* 47:e2020GL090797. https://doi.org/10.1029/2020GL090797
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Tanigawa T, Ohtsuki K, Machid MN (2012) Distribution of accreting gas and angular momentum onto circumplanetary disks. Astrophys J 747:47-63. https://doi.org/10.1088/0004-637X/747/1/47

Tassi F, Vaselli O, Capaccioni B, Montegrossi G, Barahona F, Capari A (2007) Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: an example from the geothermal fields of El Salvador. Geochem Geophys Geosyst 8(5). https://doi.org/10.1029/2006GC001487

Trinh KT, Bierson CJ, O'Rourke JG (2023) Slow evolution of Europa's interior: metamorphic ocean origin, delayed metallic core formation, and limited seafloor volcanism. Sci Adv 9(24). https://www.science.org/doi/10.1126/sciadv.adf3955

Trumbo SK, Brown ME, Hand KP (2019) Sodium chloride on the surface of Europa. Sci Adv 5(6):eaaw7123. https://doi.org/10.1126/sciadv.aaw7123

Trumbo SK, Becker TM, Brown ME, Denman WTP, Molyneux P, Hendrix A, Retherford KD, Roth L, Alday J (2022) A new UV spectral feature on Europa: confirmation of NaCl in leading-hemisphere chaos terrain. Planet Sci J 3:27. https://doi.org/10.3847/PSJ/ac4580

Vance SD, Harnmeijer J, Kimura J, Hussmann H, DeMartin B, Brown JM (2007) Hydrothermal systems in small ocean planets. Astrobiology 7(6):987-1005. https://doi.org/10.1089/ast.2007.0075

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Vance SD, Hand KP, Pappalardo RT (2016) Geophysical controls of chemical disequilibria in Europa. Geophys Res Lett 43(10):4871-4879. https://doi.org/10.1002/2016GL068547

Vance SD, Barge LM, Cardoso SS, Cartwright JH (2019) Self-assembling ice membranes on Europa: brinicle properties, field examples, and possible energetic systems in icy ocean worlds. Astrobiology 19(5):685-695. https://doi.org/10.1089/ast.2018.1826

Vance SD, Styczinski MJ, Bills BG, Cochrane CJ, Soderlund KM, Gómez-Pérez N, Paty C (2021) Magnetic induction responses of Jupiter's ocean moons including effects from adiabatic convection. J Geophys Res, Planets 126:e2020JE006418. https://doi.org/10.1029/2020JE006418

Waite JH, Glein CR, Perryman RS, Teolis BD, Magee BA, Miller G, Grimes J, Perry ME, Miller KE, Bouquet A et al (2017) Cassini finds molecular hydrogen in the Enceladus plume: evidence for hydrothermal processes. Science 356(6334):155-159. https://doi.org/10.1126/science.aai8703

Waite JH et al (2024) MASPEX-Europa: the Europa Clipper neutral gas mass spectrometer investigation. Space Sci Rev 220

White LM, Shibuya T, Vance SD, Christensen LE, Bhartia R, Kidd R, Hoffmann A, Stucky GD, Kanik I, Russell MJ (2020) Simulating serpentinization as it could apply to the emergence of life using the JPL hydrothermal reactor. Astrobiology 20(3):307-326. https://doi.org/10.1089/ast.2018.1949

Wolfenbarger NS, Buffo JJ, Soderlund KM Blankenship DD (2022a) Ice shell structure and composition of ocean worlds: insights from accreted ice on Earth. Astrobiology 22:937-961. https://doi.org/10.1089/ast.2021.0044

Wolfenbarger NS, Fox-Powell MG, Buffo JJ, Soderlund KM, Blankenship DD (2022b) Compositional controls on the distribution of brine in Europa's ice shell. J Geophys Res, Planets 127(9):e2022JE007305. https://doi.org/10.1029/2022JE007305

Yoder CF, Peale SJ (1981) The tides of Io. Icarus 47:1-35. https://doi.org/10.1016/0019-1035(81)90088-9

Zahnle K, Schenk P, Levison H, Dones L (2003) Cratering rates in the outer Solar System. Icarus 163(2):263-289. https://doi.org/10.1016/S0019-1035(03)00048-4

Zeebe R, Caldeira K (2008) Close mass balance of long-term carbon fluxes from ice-core CO2 and ocean chemistry records. Nat Geosci 1:312-315. https://doi.org/10.1038/ngeo185

Zhang Z, Bolton SJ, Brown S, Bonnefoy LE, Ermakov A, Feng J, Keane J, Levin S, Lunine J, Leonard E, Misra S, Martinez A, Hartogh P, Stevenson D, Siegler M (2023) Juno microwave radiometer observations of Europa's ice shell. In: 54th Lunar Planet Sci Conf, LPI. Abstract 2314

Zhu P, Manucharyan G, Thompson AF, Goodman J, Vance SD (2017) The influence of meridional ice transport on Europa's ocean stratification and heat content. Geophys Res Lett 44. https://doi.org/10.1002/2017GL072996
Styczinski MJ, Cooper ZS, Glaser DM, Lehmer O, Mierzejewski V, Tarnas J (2022) Chap. 7: assessing habitability beyond Earth. In: Astrobiology Primer 3.0. 2022 astrobiology science conference. Am. Geophys. Union, Washington

Szulágyi J, Masset F, Lega E, Crida A, Morbidelli A, Guillot T (2016) Circumplanetary disc or circumplanetary envelope? Mon Not R Astron Soc 460:2853-2861. https://doi.org/10.1093/mnras/stw1160

Tan S, Sekine Y, Shibuya T, Miyamoto C, Takahashi Y (2021) The role of hydrothermal sulfate reduction in the sulfur cycles within Europa: laboratory experiments on sulfate reduction at 100 MPa. Icarus 357:114222. https://doi.org/10.1016/j.icarus.2020.114222

Tanigawa T, Ohtsuki K, Machid MN (2012) Distribution of accreting gas and angular momentum onto circumplanetary disks. Astrophys J 747:47-63. https://doi.org/10.1088/0004-637X/747/1/47

Tassi F, Vaselli O, Capaccioni B, Montegrossi G, Barahona F, Capari A (2007) Scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges: an example from the geothermal fields of El Salvador. Geochem Geophys Geosyst 8(5). https://doi.org/10.1029/2006GC001487

Trinh KT, Bierson CJ, O'Rourke JG (2023) Slow evolution of Europa's interior: metamorphic ocean origin, delayed metallic core formation, and limited seafloor volcanism. Sci Adv 9(24). https://www.science.org/doi/10.1126/sciadv.adf3955

Trumbo SK, Brown ME, Hand KP (2019) Sodium chloride on the surface of Europa. Sci Adv 5(6):eaaw7123. https://doi.org/10.1126/sciadv.aaw7123

Trumbo SK, Becker TM, Brown ME, Denman WTP, Molyneux P, Hendrix A, Retherford KD, Roth L, Alday J (2022) A new UV spectral feature on Europa: confirmation of NaCl in leading-hemisphere chaos terrain. Planet Sci J 3:27. https://doi.org/10.3847/PSJ/ac4580

Vance SD, Harnmeijer J, Kimura J, Hussmann H, DeMartin B, Brown JM (2007) Hydrothermal systems in small ocean planets. Astrobiology 7(6):987-1005. https://doi.org/10.1089/ast.2007.0075

Vance S, Bouffard M, Choukroun M, Sotin C (2014) Ganymede's internal structure including thermodynamics of magnesium sulfate oceans in contact with ice. Planet Space Sci 96:62-70. https://doi.org/10.1016/j.pss.2014.03.011

Vance SD, Hand KP, Pappalardo RT (2016) Geophysical controls of chemical disequilibria in Europa. Geophys Res Lett 43(10):4871-4879. https://doi.org/10.1002/2016GL068547

Vance SD, Barge LM, Cardoso SS, Cartwright JH (2019) Self-assembling ice membranes on Europa: brinicle properties, field examples, and possible energetic systems in icy ocean worlds. Astrobiology 19(5):685-695. https://doi.org/10.1089/ast.2018.1826

Vance SD, Styczinski MJ, Bills BG, Cochrane CJ, Soderlund KM, Gómez-Pérez N, Paty C (2021) Magnetic induction responses of Jupiter's ocean moons including effects from adiabatic convection. J Geophys Res, Planets 126:e2020JE006418. https://doi.org/10.1029/2020JE006418

Waite JH, Glein CR, Perryman RS, Teolis BD, Magee BA, Miller G, Grimes J, Perry ME, Miller KE, Bouquet A et al (2017) Cassini finds molecular hydrogen in the Enceladus plume: evidence for hydrothermal processes. Science 356(6334):155-159. https://doi.org/10.1126/science.aai8703

Waite JH et al (2024) MASPEX-Europa: the Europa Clipper neutral gas mass spectrometer investigation. Space Sci Rev 220

White LM, Shibuya T, Vance SD, Christensen LE, Bhartia R, Kidd R, Hoffmann A, Stucky GD, Kanik I, Russell MJ (2020) Simulating serpentinization as it could apply to the emergence of life using the JPL hydrothermal reactor. Astrobiology 20(3):307-326. https://doi.org/10.1089/ast.2018.1949

Wolfenbarger NS, Buffo JJ, Soderlund KM Blankenship DD (2022a) Ice shell structure and composition of ocean worlds: insights from accreted ice on Earth. Astrobiology 22:937-961. https://doi.org/10.1089/ast.2021.0044

Wolfenbarger NS, Fox-Powell MG, Buffo JJ, Soderlund KM, Blankenship DD (2022b) Compositional controls on the distribution of brine in Europa's ice shell. J Geophys Res, Planets 127(9):e2022JE007305. https://doi.org/10.1029/2022JE007305

Yoder CF, Peale SJ (1981) The tides of Io. Icarus 47:1-35. https://doi.org/10.1016/0019-1035(81)90088-9

Zahnle K, Schenk P, Levison H, Dones L (2003) Cratering rates in the outer Solar System. Icarus 163(2):263-289. https://doi.org/10.1016/S0019-1035(03)00048-4

Zeebe R, Caldeira K (2008) Close mass balance of long-term carbon fluxes from ice-core CO2 and ocean chemistry records. Nat Geosci 1:312-315. https://doi.org/10.1038/ngeo185

Zhang Z, Bolton SJ, Brown S, Bonnefoy LE, Ermakov A, Feng J, Keane J, Levin S, Lunine J, Leonard E, Misra S, Martinez A, Hartogh P, Stevenson D, Siegler M (2023) Juno microwave radiometer observations of Europa's ice shell. In: 54th Lunar Planet Sci Conf, LPI. Abstract 2314

Zhu P, Manucharyan G, Thompson AF, Goodman J, Vance SD (2017) The influence of meridional ice transport on Europa's ocean stratification and heat content. Geophys Res Lett 44. https://doi.org/10.1002/2017GL072996
Zolotov MY (2008) Oceanic composition on Europa: constraints from mineral solubilities. In: Lunar and planetary institute science conference, p 2349

Zolotov MY (2020) The composition and structure of Ceres' interior. Icarus 335:113404. https://doi.org/10.1016/j.icarus.2019.113404

Zolotov MY, Kargel JS (2009) On the chemical composition of Europa's icy shell, ocean, and underlying rocks. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. University of Arizona Press, Tucson, pp 431–458

Zolotov MY, Shock EL (2001) Composition and stability of salts on the surface of Europa and their oceanic origin. J Geophys Res, Planets 106(E12):32815–32827. https://doi.org/10.1029/2000JE001413

Zolotov MY, Shock EL (2003) Energy for biologic sulfate reduction in a hydrothermally formed ocean on Europa. J Geophys Res 108(E4):5022. https://doi.org/10.1029/2002JE001966

Zolotov MY, Shock EL (2004) A model for low-temperature biogeochemistry of sulfur, carbon, and iron on Europa. J Geophys Res, Planets 109(6):1–16. https://doi.org/10.1029/2003JE002194

**Publisher's Note** Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Authors and Affiliations

Steven D. Vance¹ · Kathleen L. Craft² · Everett Shock³ · Britney E. Schmidt⁴ ·

Jonathan Lunine⁴ · Kevin P. Hand¹ · William B. McKinnon⁵ · Elizabeth M. Spiers⁶ ·

Chase Chivers⁶,⁷ · Justin D. Lawrence⁶,⁸ · Natalie Wolfenbarger⁹ · Erin J. Leonard¹ ·

Kirtland J. Robinson¹⁰ · Marshall J. Styczinski¹ · Divya M. Persaud¹ ·

Gregor Steinbrügge¹ · Mikhail Y. Zolotov³ · Lynnae C. Quick¹¹ · Jennifer E.C. Scully¹ ·

Tracy M. Becker¹² · Samuel M. Howell¹ · Roger N. Clark¹³ · Andrew J. Dombard¹⁴ ·

Christopher R. Glein¹² · Olivier Mousis¹⁵ · Mark A. Sephton¹⁶ · Julie Castillo-Rogez¹ ·

Francis Nimmo¹⁷ · Alfred S. McEwen¹⁸ · Murthy S. Gudipati¹ · Insoo Jun¹ ·

Xianzhe Jia¹⁹ · Frank Postberg²⁰ · Krista M. Soderlund⁹ · Catherine M. Elder¹

<figure><img src="image_14.png" /></figure>

S.D. Vance

Steven.D.Vance@jpl.nasa.gov

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

2 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA

3 School of Earth & Space Exploration and School of Molecular Sciences, Arizona State University, Tempe, AZ, USA

4 Department of Astronomy and Department of Earth & Atmospheric Sciences, Cornell University, Ithaca, NY, USA

5 Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, Saint Louis, MO, USA

6 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

7 Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

8 Honeybee Robotics, Altadena, CA, USA

9 Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA

10 Beyond Center, Arizona State University, Tempe, AZ, USA

11 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Zolotov MY (2008) Oceanic composition on Europa: constraints from mineral solubilities. In: Lunar and planetary institute science conference, p 2349

Zolotov MY (2020) The composition and structure of Ceres' interior. Icarus 335:113404. https://doi.org/10.1016/j.icarus.2019.113404

Zolotov MY, Kargel JS (2009) On the chemical composition of Europa's icy shell, ocean, and underlying rocks. In: Pappalardo RT, McKinnon WB, Khurana KK (eds) Europa. University of Arizona Press, Tucson, pp 431–458

Zolotov MY, Shock EL (2001) Composition and stability of salts on the surface of Europa and their oceanic origin. J Geophys Res, Planets 106(E12):32815–32827. https://doi.org/10.1029/2000JE001413

Zolotov MY, Shock EL (2003) Energy for biologic sulfate reduction in a hydrothermally formed ocean on Europa. J Geophys Res 108(E4):5022. https://doi.org/10.1029/2002JE001966

Zolotov MY, Shock EL (2004) A model for low-temperature biogeochemistry of sulfur, carbon, and iron on Europa. J Geophys Res, Planets 109(6):1–16. https://doi.org/10.1029/2003JE002194

**Publisher's Note** Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Authors and Affiliations

Steven D. Vance¹ · Kathleen L. Craft² · Everett Shock³ · Britney E. Schmidt⁴ ·

Jonathan Lunine⁴ · Kevin P. Hand¹ · William B. McKinnon⁵ · Elizabeth M. Spiers⁶ ·

Chase Chivers⁶,⁷ · Justin D. Lawrence⁶,⁸ · Natalie Wolfenbarger⁹ · Erin J. Leonard¹ ·

Kirtland J. Robinson¹⁰ · Marshall J. Styczinski¹ · Divya M. Persaud¹ ·

Gregor Steinbrügge¹ · Mikhail Y. Zolotov³ · Lynnae C. Quick¹¹ · Jennifer E.C. Scully¹ ·

Tracy M. Becker¹² · Samuel M. Howell¹ · Roger N. Clark¹³ · Andrew J. Dombard¹⁴ ·

Christopher R. Glein¹² · Olivier Mousis¹⁵ · Mark A. Sephton¹⁶ · Julie Castillo-Rogez¹ ·

Francis Nimmo¹⁷ · Alfred S. McEwen¹⁸ · Murthy S. Gudipati¹ · Insoo Jun¹ ·

Xianzhe Jia¹⁹ · Frank Postberg²⁰ · Krista M. Soderlund⁹ · Catherine M. Elder¹

<figure><img src="image_14.png" /></figure>

S.D. Vance

Steven.D.Vance@jpl.nasa.gov

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

2 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA

3 School of Earth & Space Exploration and School of Molecular Sciences, Arizona State University, Tempe, AZ, USA

4 Department of Astronomy and Department of Earth & Atmospheric Sciences, Cornell University, Ithaca, NY, USA

5 Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, Saint Louis, MO, USA

6 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

7 Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

8 Honeybee Robotics, Altadena, CA, USA

9 Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA

10 Beyond Center, Arizona State University, Tempe, AZ, USA

11 NASA Goddard Space Flight Center, Greenbelt, MD, USA
12 Southwest Research Institute, San Antonio, TX, USA

13 Planetary Science Institute, Tucson, AZ, USA

14 Dept. of Earth and Environmental Sciences, University of Illinois Chicago, Chicago, USA

15 Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), Marseille, France

16 Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, United Kingdom

17 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA

18 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

19 Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA

20 Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
12 Southwest Research Institute, San Antonio, TX, USA

13 Planetary Science Institute, Tucson, AZ, USA

14 Dept. of Earth and Environmental Sciences, University of Illinois Chicago, Chicago, USA

15 Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), Marseille, France

16 Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, United Kingdom

17 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA

18 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

19 Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA

20 Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany