Icy ocean worlds - astrobiology research in Germany [original]

TYPE Review

PUBLISHED 14 August 2024

DOI 10.3389/fspas.2024.1422898

OPEN ACCESS

EDITED BY

Josep M. Trigo-Rodríguez,

Spanish National Research Council

(CSIC), Spain

REVIEWED BY

Akos Kereszturi,

Hungarian Academy of Sciences

(MTA), Hungary

Alfonso F. Davila,

National Aeronautics and Space

Administration, United States

*CORRESPONDENCE

Fabian Klenner,

[email protected]

Jean-Pierre Paul de Vera,

jean-pierre.devera@dlr.de

RECEIVED 24 April 2024

ACCEPTED 22 July 2024

PUBLISHED 14 August 2024

CITATION

Klenner F, Baqué M, Beblo-Vranesevic K,

Bönigk J, Boxberg MS, Dachwald B, Digel I,

Elsaesser A, Espe C, Funke O, Hauber E,

Heinen D, Hofmann F, Hortal Sánchez L,

Khawaja N, Napoleoni M, Plesa A-C,

Postberg F, Purser A, Rückriemen-Bez T,

Schröder S, Schulze-Makuch D, Ulamec S and

de Vera J-PP (2024), Icy ocean worlds -

astrobiology research in Germany.

Front. Astron. Space Sci. 11:1422898.

doi: 10.3389/fspas.2024.1422898

Bönigk, Boxberg, Dachwald, Digel, Elsaesser,

Espe, Funke, Hauber, Heinen, Hofmann,

Hortal Sánchez, Khawaja, Napoleoni, Plesa,

Postberg, Purser, Rückriemen-Bez, Schröder,

Schulze-Makuch, Ulamec and de Vera. This is

an open-access article distributed under the

terms of the Creative Commons Attribution

License (CC BY). The use, distribution or

reproduction in other forums is permitted,

provided the original author(s) and the

original publication in this journal is cited, in

accordance with accepted academic practice.

No use, distribution or reproduction is

permitted which does not comply with

these terms.

Icy ocean worlds - astrobiology

research in Germany

Fabian Klenner1*, Mickael Baqué2, Kristina Beblo-Vranesevic3,

Janine Bönigk4, Marc S. Boxberg5, Bernd Dachwald6, Ilya Digel7,

Andreas Elsaesser8, Clemens Espe9, Oliver Funke10,

Ernst Hauber2, Dirk Heinen11, Florence Hofmann8, Lucía Hortal

Sánchez4, Nozair Khawaja4,12, Maryse Napoleoni4,

Ana-Catalina Plesa2, Frank Postberg4, Autun Purser13,

Tina Rückriemen-Bez2, Susanne Schröder14,

Dirk Schulze-Makuch15,16,17,18, Stephan Ulamec19 and

Jean-Pierre Paul de Vera19*

1Department of Earth and Space Sciences, University of Washington, Seattle, WA, United States,

2Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany, 3Institute of

Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany, 4Institute of Geological

Sciences, Freie Universität Berlin, Berlin, Germany, 5Geophysical Imaging and Monitoring, RWTH

Aachen University, Aachen, Germany, 6Faculty of Aerospace Engineering, FH Aachen University of

Applied Sciences, Aachen, Germany, 7Institut für Bioengineering, FH Aachen University of Applied

Sciences, Jülich, Germany, 8Experimental Space Science and Biophysics, Freie Universität Berlin,

Berlin, Germany, 9GSI - Gesellschaft für Systementwicklung and Instrumentierung mbH, Aachen,

Germany, 10German Space Agency at DLR, German Aerospace Center (DLR), Bonn, Germany, 11Physics

Institute III B, RWTH Aachen University, Aachen, Germany, 12Institute of Space Systems, University of

Stuttgart, Stuttgart, Germany, 13Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine

Research, Bremerhaven, Germany, 14Institute of Optical Sensor Systems, German Aerospace Center

(DLR), Berlin, Germany, 15Astrobiology Group, Center of Astronomy and Astrophysics, Technische

Universität Berlin, Berlin, Germany, 16Section Geomicrobiology, GFZ German Research Center for

Geosciences, Potsdam, Germany, 17Department of Plankton and Microbial Ecology, Leibniz-Institute

of Freshwater Ecology and Inland Fisheries (IGB), Stechlin, Germany, 18School of the Environment,

Washington State University, Pullman, WA, United States, 19Microgravity User Support Center (MUSC),

Space Operations and Astronaut Training, German Aerospace Center (DLR), Cologne, Germany

Icy bodies with subsurface oceans are a prime target for astrobiology

investigations, with an increasing number of scientists participating in the

planning, development, and realization of space missions to these worlds. Within

Germany, the Ocean Worlds and Icy Moons working group of the German

Astrobiology Society provides an invaluable platform for scientists and engineers

from universities and other organizations with a passion for icy ocean worlds to

share knowledge and start collaborations. We here present an overview about

astrobiology research activities related to icy ocean worlds conducted either

in Germany or in strong collaboration with scientists in Germany. With recent

developments, Germany offers itself as a partner to contribute to icy ocean

world missions.

KEYWORDS

subsurface oceans, space missions, habitability, icy moons, solar system exploration,

Deutsche Astrobiologische Gesellschaft (DAbG), ocean worlds, German Aerospace

Center (DLR)

Frontiers in Astronomy and Space Sciences 01 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

1 Introduction: past and future

exploration of icy ocean worlds

The German space science community and particularly

the German Astrobiology Society (Deutsche Astrobiologische

Gesellschaft; DAbG) has a deep scientific interest in space

exploration. In 2023, the German Government published its space

program strategy (BMWK, 2023) by explicitly mentioning the

value of space research, technology developments and exploration

for the society in general. The strategic view formulated in this

document is to support synergy of different competences, expertise

and resources to allow on the one hand space research and space

exploration leading to international space missions and on the other

hand the use of space related technology via technology transfer

also in society relevant topics such as climate and environmental

protectionas well as discoveringandusing sustainable resources.We

will here start with an overview on the general scientific interest and

space missions as well as showing the German participation and/or

interest in the present and future exploration missions particularly

to the icy moons of Jupiter and Saturn. We further describe the

technology developments and scientific strategy including planetary

analog field research, laboratory experiments, numerical simulation

investigations and even space experiments in Earth’s orbit. At the

end, the context of German space exploration activities to the

German political strategy in reference to the exploration of the

icy ocean worlds will be highlighted. Technology developed for

future missions will be able to be transferred to disciplines related

to polar-, ocean-, deep sea- and climate change-research to address

fundamental scientific questions related to our home planet Earth.

The first enlightening visits of the giant planets and their

moons by spacecraft (Pioneer 10/11 in 1973–1990, Voyager 1/2

in 1979–1989) led to an increasing interest to further investigate

those planetary systems as key elements for understanding the

Solar System as a whole. Measurements by Galileo in the Jovian

(in 1995–2003) and Cassini-Huygens in the Saturnian system (in

2004–2017) revealed the existence of subsurface oceans under the

ice shells of, for example, Jupiter’s moons Europa and Ganymede

as well as Saturn’s moon Enceladus (e.g., Nimmo and Pappalardo,

2016). The Cassini-Huygens mission discovered a plume emanating

from the south pole of Saturn’s moon Enceladus (Porcoetal., 2006).

This plume emerges from cracks in the ice shell and consequent

studies revealed its composition to be mainly water vapor and

ice particles originating from a subsurface ocean, with a salinity

slightly lower than Earth’s oceans (Postbergetal., 2009). Finding

analogue sites for extraterrestrial icy vents and plumes here on

Earth is challenging due to the triple point conditions present inside

the icy vents of Enceladus (Schmidtetal., 2008), derived from the

drastic difference in pressure between the interior and exterior of

the moon. Analogies to the environment near terrestrial, submarine

hydrothermal vents, a potential site for the origin of life on the

early Earth were striking and the icy moons became promising

candidates for habitable worlds and prime targets for astrobiology

investigations.

Alike Enceladus, Europa harbors a global subsurface liquid

water ocean that is in contact with a rocky core (e.g., Kivelsonetal.,

2000). Ganymede’s subsurface ocean is probably sandwiched

between two layers of ice (Vanceetal., 2014;Sauretal., 2015),

making material exchange between the liquid ocean and the core

less likely. The same applies to Jupiter’s moon Callisto (Hartkorn and

Saur, 2017). Saturn’s moon Titan has a liquid, likely stratified (Idini

and Nimmo, 2024), water ocean underneath its organic-covered ice

shell (Goossensetal., 2024). Neptune’s moon Triton is another, yet

widely unexplored, ocean world and a compelling destination for

future space mission (Frazieretal., 2020;Hansenetal., 2021).

Our current understanding of the oceans of the icy moons and

the fascinating discoveries by spacecraft in the recent past (e.g.,

Enceladus’s plume) will be discussed in some detail in the following

chapters. However, many questions could not be answered so far,

which led to the development of numerous mission proposals to

further investigate the oceans of the icy moons (e.g., Howell and

Pappalardo, 2020;Barnesetal., 2021;Mousisetal., 2022).

After the end of the Cassini-Huygens mission in 2017, the flybys

of Ganymede and Europa of the Juno spacecraft in 2022 and 2023,

as part of its extended mission, are the only occasions of a spacecraft

visiting ocean moons in the 2020s. This lack is partially mitigated

by the spectacular observations of the James Webb Space Telescope

of the moons Europa (Villanuevaetal., 2023a;Trumbo and Brown,

2023) and Enceladus (Villanuevaetal., 2023b). Although these

observations yield better data than any other telescopic observation,

the spatial resolution of the James Webb Space Telescope, even for

the Jovian moons, is still four to five orders of magnitude below what

can be achieved with a close flyby.

However, starting in 2030, ocean moons will become more

important targets of both NASA’s and ESA’s space programs. In

2030 and 2031 respectively, two flagship missions - Europa Clipper

(NASA) and the JUpiter Icy Moons Explorer (JUICE; ESA) -

will arrive in the Jovian System to observe Europa, Ganymede,

and Callisto as their prime targets. Both missions Europa Clipper

(Howell and Pappalardo, 2020) and JUICE (Grasset etal., 2013) have

significant German contributions, advancing the research in this

field at German research facilities (Figure1).

Europa Clipper is scheduled for launch in October 2024 and

has the overarching goal to constrain the habitability of Europa’s

subsurface ocean with about 50 close flybys within the 4 years of

its prime mission while in orbit around Jupiter (Vanceetal., 2023).

The locations of these flybys are all fixed in form of a flyby sequence,

but a potential extended mission could allow for targeted flybys over

regions that have turned out to be of specific interest for Europa’s

habitability.

JUICE (launched 14 April 2023) has a somewhat broader scope.

During the first part of the mission the spacecraft will stay in a Jovian

orbit with two flybys of Europa and tens of flybys of each Callisto and

Ganymede. In December 2034, ESA plans to go into Ganymede orbit

for a detailed investigation of the largest moon in the Solar System.

After up to 1year in Ganymede orbit a crash onto the moon’s surface

will then end the JUICE mission.

Titan will be visited by the spectacular Dragonfly mission in

the mid 2030s. Currently, the launch of this NASA New Frontier

class mission is foreseen in 2028 with an arrival in 2034. The

spacecraft is a rotorcraft lander weighing about 450kg, that - driven

by radioisotope thermoelectric generators (RTG) – will sample the

moon’s atmosphere and surface composition at different landing

sites to assess Titan’s potentially prebiotic organic chemistry. The

combination of low gravity and dense atmosphere allow the drone-

like lander to investigate various sites and altitudes during its

Frontiers in Astronomy and Space Sciences 02 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

FIGURE 1

Locations of research groups in Germany with ongoing astrobiology research and collaborations related to icy ocean worlds. Research themes are

summarized in Table1. The German Astrobiology Society (Deutsche Astrobiologische Gesellschaft; DAbG) logo is shown on the bottom right.

Institutions where DAbG members are currently located are marked with an asterisk.

3.5-year prime mission by flying distances of up to 100km while

climbing to altitudes of up to several kilometers (Barnes etal., 2023).

Beyond these approved missions, there are long term strategies

of space agencies, most notably NASA, ESA and the China National

Space Administration (CNSA), to investigate the giant planets

and their icy moons. On the U.S. side, this is outlined in the

Planetary Science and Astrobiology Decadal Survey 2023–2032

(NationalAcademiesofSciences,Engineering, and Medicine, 2023)

as well as in reports written by the Outer Planets Assessment

Group (OPAG), established in 2004 (Beauchampetal., 2009). The

NASA competitive programs, Discovery and New Frontiers (NF),

include the possibility to propose missions to icy ocean worlds. New

Horizons (NF1) performed a flyby of dwarf planet Pluto. JUNO

(NF2) is in orbit around Jupiter. The aforementioned Dragonfly has

been selected as the fourth New Frontiers mission (Barnesetal.,

2021). All those missions have relevance to icy ocean worlds

exploration.

The Planetary Science and Astrobiology Decadal Survey

2023–2032 foresees up to three major missions in the near future.

Firstly, the next New Frontiers mission (NF5) lists Enceladus

as a potential target. Moreover, the next two flagship missions

should be a Uranus orbiter and an Enceladus lander. Following

the Orbilander concept (MacKenzieetal., 2021), the latter would

be a mission that looks for life on Saturn’s active ocean moon

with a planned arrival in the early 2050s. Already sometime

earlier the Uranus orbiter would arrive and the exploration of the

Uranian moons, some of which are potential ocean worlds, will

certainly be part of the mission goals. ESA considers contributing

to this Uranus mission in a similar fashion as it has been

successfully implemented for the joint Cassini-Huygens mission

whereESA provided theHuygensprobe that landed onTitanin 2005

(Lebretonetal., 2005).

At ESA, the long-term priorities in space sciences are described

in the Voyage 2050 report (Tacconietal., 2021), which identifies

a mission to “moons of the giant planets” as the fourth large

mission (L4) in the science program (following JUICE, Athena

and LISA) as well as a so-called “Inspirator Mission”, aiming for

sample return from one of the icy moons (Rapleyetal., 2022).

With a launch date in the early 2040s, Enceladus is the most

likely target for this L4 mission, as recently announced by ESA

(Martinsetal., 2024).

China is also planning to investigate the Jovian system with the

Tianwen-4 mission (also referred to as Gan De, after a Chinese

astronomer of the 4th century). As a possible launch date, 2029 has

been announced (Leietal., 2021). It is worth noting that currently

there are no concrete plans to land on a Jovian satellite, and

even less so to physically penetrate the ice crust. Although many

ideas were addressed and the concept of a Europa lander mission

was studied (Handetal., 2022), this concept was not rated as a high-

priority mission. Nevertheless, some astrobiological questions will

only be answered by lander missions or melting/drilling probes. For

example, limiting elements of life, such as iron, may be remotely

Frontiers in Astronomy and Space Sciences 03 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

detectable on the surface in flybys, but in situ analyses with a lander

provides spatially better resolved and much more detailed and

sensitive measurements. Other space agencies, e.g., Russia, Japan, or

India, currently do not have plans for ocean moon exploration.

2 Activities in Germany - general

overview

In the last decades there has been increasing activities in

Germany to investigate icy ocean moons to realize future space

missions to these worlds. DAbG Members (Figure1;Table1)

are heavily involved in both missions to the Jovian system

JUICE and Europa Clipper. Involvements include participations

in various instrument teams, such as the Particle Environment

Package-Neutral Ion Mass Spectrometer (PEP-NIM; Barabashetal.,

2013), the JANUS multispectral camera (DellaCorteetal., 2014)

and the Ganymede Laser Altimeter GALA (Enyaetal., 2022)

for JUICE as well as the SUrface Dust Analyzer (SUDA) for

Europa Clipper (Kempfetal., 2024).

2.1 Explorer Initiatives at the German

Aerospace Center

Since 2012, the Explorer Initiatives at the German Aerospace

Center (DLR) have been supporting universities, research

institutions and commercial companies from all over Germany

in specially created project lines. The aim of these project lines

is to develop innovative technologies to enable future space

missions to astrobiologically interesting celestial bodies in our

Solar System (Funke and Horneck, 2018). Each project line is based

on a central, albeit currently fictitious, mission scenario:

In the EnEx initiative (“EnEx - Enceladus Explorer”; Kowalski

etal., 2016), technologies are being developed for taking a H2O

sample from a vent on Saturn’s moon Enceladus. The sample can

be taken without completely melting through the moon’s outer ice

shield, which is several kilometers thick.

Jupiter’s moon Europa is also receiving special attention, here

in the project lines “EurEx - Europa Explorer”, and “TRIPLE

- Technologies for Rapid Ice Penetration and subglacial Lake

Exploration”:

In EurEx, an autonomous underwater vehicle (AUV) is being

developed to explore the seabed of the deep global ocean on Europa

completely independently (Hildebrandtetal., 2022). The challenges

are enormous, particularly in terms of the AI required for this task,

and successful implementation is not expected before the middle of

this century.

While EurEx has a long-term focus, the TRIPLE project line

has a medium-term objective (Waldmann and Funke, 2020): The

plan is to develop an AUV that is even more miniaturized than the

EurEx AUV. This nanoAUV is designed as a payload for a melting

probe, which is designed to penetrate the ice sheet of Europa into

the global ocean below (see also Section 3). The melting probe will

be anchored in the ice at the point of entry into the ocean and will

serve as a base to ensure communication to the surface and from

there to Earth. The nanoAUV payload will then be deployed into

the ocean as a mobile unit and will be used for exploration within a

radius of approximately 100m around the base. The nanoAUV will

also be used to take samples from the bottom side of the ice and

bring these samples to the melting probe for further analysis within

the AstroBioLab, which is another payload of the probe. It is planned

to demonstrate the technological readiness of the complete TRIPLE

system consisting of three major parts: The melting probe TRIPLE-

IceCraft (Figure2), the mobile exploration unit TRIPLE-nanoAUV

and the TRIPLE-AstroBioLab.

These three main components are designed to work together

as consecutive stages of the TRIPLE comprehensive exploration

strategy. With its state-of-the-art instrumentation, the AstroBioLab

serves as the portable analytical field hub for analyzing samples

previously collected under the ice and transported to the surface.

2.2 The AstroBioLab

The AstroBioLab analytical pipeline consists of four modalities:

(a) fluorescence spectroscopy, (b) fluorescence microscopy, (c)

DNA sequencing and (d) mass spectrometry interconnected by a

sophisticated microfluidics system.

Fluorescence spectroscopy (a), especially when coupled with

Chromophoric Dissolved Organic Matter (CDOM) analysis

principles, emerges as a powerful tool in astrobiology, particularly

for scrutinizing extraterrestrial environments or seeking signs of

life (Barkeretal., 2009;Smithetal., 2018). Unique combinations of

fluorescence intensity, peak shapes and exact positions produce

characteristic spectral patterns that shed light on CDOM’s

composition, concentration and even its origin. Extensive testing

in Arctic ice, Antarctic lakes and deep-sea hydrothermal vents

has demonstrated the effectiveness of fluorescence spectroscopy

in studying complex aquatic ecosystems and in detecting organic

compounds under conditions analogous to those found on

other planets (Storrie-Lombardi and Sattler, 2009). For instance,

fluorescence analysis of water samples from Antarctic lakes

revealed significant photosynthetic and biodegradation activities,

(DeLaurentiisetal.,2013).Tomeetthefuture missionrequirements

regarding miniaturization, energy consumption, robustness and

easy handling, a semi-automatic fluorimeter module has been

designed and manufactured by the FH Aachen University of Applied

Sciences and GSI mbH (Figure3).

Fluorescence microscopy (b) will enable direct visualization

of particulate matter, ranging from submicron to submillimeter

size (e.g., Mulyukinetal., 2014). Studies in Earth’s polyextreme

environments like the Atacama Desert have shown the potential

of this technology in visualizing and identifying microbial life

forms in various microhabitats (Wierzchosetal., 2018). In future

field missions, miniaturized automated fluorescence microscopy

systems such as OpenFlexure (which can be 3D printed), can be

deployed for in situ exploration, thereby diminishing the necessity

for sample return. Furthermore, employing advanced fluorescence

techniques, such as lifetime imaging microscopy, may provide

additional insights into the microenvironment of (extra) terrestrial

water samples (Nadeauetal., 2016).

DNA sequencing (c) is yet another valuable tool for

exploring icy ocean habitats (e.g., Carréetal., 2024). Field tests

in locations like Antarctica’s subglacial lakes and Canadian high

arctic permafrost ice wedge have validated the feasibility of

Frontiers in Astronomy and Space Sciences 04 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

TABLE 1 Institutes in Germany (see Figure1) and their icy ocean world research themes.

Institute Research themes Web links (on 01 August 2024)

Alfred Wegener Institute Bremerhaven Arctic research, nanoAUV sample return system, Life

detection

https://www.awi.de/en/focus/mosaic-expedition.html

Bergische Universität Wuppertal TRIPLE Forefield Reconnaissance System (FRS) https://www.uni-wuppertal.de/en

DSI Aerospace GmbH nanoAUV avionics https://www.dsi.space/

Deutsches Zentrum für Luft und Raumfahrt (DLR),

Institute of Aerospace Medicine, Cologne

Laboratory experiments, Space simulation facilities,

Life detection efforts, Participation in ESA’s space

experiment IceCold (PI Elke Rabbow)

https://www.dlr.de/en/dlr/locations-and-

offices/cologne

https://www.dlr.de/me/en/desktopdefault.aspx/tabid-

7207/

Deutsches Zentrum für Luft und Raumfahrt (DLR),

Space Operations and Astronaut Training,

Microgravity User Support Center (MUSC), Cologne

Operations of experiments during field studies, in Low

Earth Orbit (ISS), on the Moon (LUNA connected

with the DLR Human Exploration Control Centre), in

the Solar System and on ground; hardware tests,

evaluation of operation procedures; integrated

astrobiology and planetary science topics, leading

ESA’s next space experiment on board the ISS: BioSigN

(PI Jean-Pierre de Vera)

https://www.dlr.de/en/rb/about-

us/departments/microgravity-user-support-center-

musc

Deutsches Zentrum für Luft und Raumfahrt (DLR,

Institute of Planetary Research, Berlin

Laboratory and numerical simulations of subsurface

processes, Environmental chambers and

measurements in the Planetary Spectroscopy

Laboratory (PSL) as well as the astrobiological

Planetary Analog Simulation Laboratories (PASLAB)

and Raman Mineral and Biosignature detection

(RMBD) laboratory, Instrument participation in ESA’s

JUICE mission (Laser Altimeter GALA: PI Hauke

Hussmann; Camera JANUS: Co-PI Ganna

Portyankina); BioSigN Co-PI Mickael Baqué

https://www.dlr.de/en/pf

EvoLogics GmbH TRIPLE nanoAUV development https://evologics.de/

FH Aachen University of Applied Sciences Exploration of icy vent systems, In-situ

decontamination procedures, Life detection systems,

Melting probe technology

https://www.fh-aachen.de/en/

Freie Universität Berlin Laboratory and numerical investigations of subsurface

oceans and plumes, Analysis of spacecraft data,

Research on natural analogues from polar locations

https://www.geo.fu-berlin.

de/en/geol/fachrichtungen/planet/index.html

https://www.elsaesserlab.space

Friedrich-Alexander-Universität Erlangen-Nürnberg TRIPLE FRS https://www.fau.eu

German Research Center for Artificial Intelligence Under ice navigation, TRIPLE Launch and Recovery

System (LRS)

https://www.dfki.de/en/web

Gesellschaft für Systementwicklung und

Instrumentierung mbH

TRIPLE IceCraft melting probe development https://www.gsi-systems.de/

GloMic GmbH TRIPLE FRS https://www.labo.de/firma/glomic-gmbh.htm

Leibniz-Institute of Surface Engineering (IOM) Development of chemical sensors for space

applications

https://www.iom-leipzig.de/en

RWTH Aachen University TRIPLE IceCraft melting probe development, TRIPLE

Guidance, Navigation and Control (GNC) of the

nanoAUV, TRIPLE scientific payload AstroBioLab, Ice

Data Hub

https://www.rwth-aachen.de/go/id/a/?lidx=1

TriOS Mess- und Datentechnik GmbH Rastede TRIPLE in situ sensor technology as nanoAUV

payload

https://www.trios.de/en/

Technische Universität Berlin Investigation of the habitability of subsurface

environments including oceans, Instrumentation to

detect life

https://www.tu.berlin/en

(Continued on the following page)

Frontiers in Astronomy and Space Sciences 05 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

TABLE 1 (Continued) Institutes in Germany (see Figure1) and their icy ocean world research themes.

Institute Research themes Web links

Technische Universität Braunschweig JUICE magnetometer, TRIPLE LRS https://www.tu-braunschweig.de/en

University of Bremen Investigation of subsurface oceans, TRIPLE nanoAUV

development

https://www.uni-bremen.de/en/

University of Leipzig Development of chemical sensors for space applications https://www.chemie.uni-leipzig.de/en/institute-of-chemical-

technology

University of Stuttgart Calibration of hypervelocity impact detectors, such as Cassini’s

Cosmic Dust Analyzer: PI Ralf Srama

https://www.irs.uni-stuttgart.de/en/

FIGURE 2

TRIPLE-IceCraft melting probe. (A) Technical drawing showing the different parts of the melting probe, which is 4m in length and 20cm in diameter.

(B) and (C) Photographs of the melting probe during a test campaign on the Ekström Ice Shelf, Antarctica in 2023/2024. (C) shows the Upper Melting

Tip Module and the cable after the probe melted through the ice.

using portable sequencers in remote and harsh environments

(Goordialetal., 2017). Nanopore sequencers, exemplified by the

Oxford Nanopore MinION, are available as extremely compact

devices for environmental water sampling (Lietal., 2023).

However, further progress must be made in automatization of

real-time DNA sequencing where a critical step remains in

the preparation of a DNA library, which currently needs to be

performed manually.

The mass spectrometry unit (d) will provide crucial

information of elemental and molecular composition of

the sample (O'Donnelletal., 2016). Criteria related to compactness,

energy efficiency and robustness define the range of the available

options. Currently we consider the portable field mass spectrometer

EcoSys-P (ESS Ltd., Ireland) to be a promising system.

Obvious challenges to address include extremely low

temperatures, broad magnitudes of pressures, limited available

Frontiers in Astronomy and Space Sciences 06 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

FIGURE 3

Computer Aided Design (CAD; left) and photograph (right) of a miniaturized UV-fluorescence spectrometer.

power, as well as limitations in space and weight. All this demands

comprehensive interdisciplinary collaboration, coupled with

advanced engineering and AI solutions.

The scientific payload is planned to be tested by the end of this

decade in a major terrestrial analog scenario field campaign at the

Dome C region in Antarctica: There, the IceCraft (Figure 2) has to

melt through ∼3.3km of ice, avoiding any possible obstacles within

its vertical trajectory by a specially designed forefield reconnaissance

system (implemented into the melting head), and to finally get

access to a subglacial lake that has been hermetically sealed from

the environment for about 1 million years.

2.3 Beyond the Explorer Initiatives

In addition to these specific technological developments,

laboratory setups and sophisticated computer simulations are being

designed in Germany to help understand processes on icy ocean

worlds and inform instruments on board space missions (Section

4). Other projects in Germany include, for example, at DLR and

the Berlin universities, research on organics, biosignature detection

and extremophiles (Sections 5,6). Instruments on board space

missions are calibrated in laboratory experiments at, for example,,

Freie Universität Berlin and University of Stuttgart.

Another Recent development is the formation of the

international team “Bridging the Gap: From Terrestrial to Icy

Moons Cryospheres” sponsored by the International Space Science

Institute (ISSI) in Bern. The team is led by researchers from German

institutions and investigates active processes on icy moons with the

aim of bridging the temporal and spatial scales between terrestrial

and extraterrestrial cryospheres (Kowalskietal., 2024).

3 Technology and sensor

developments

Accessing ocean worlds is not trivial but crucial for in situ

astrobiological investigations. The water reservoirs of the currently

known ocean worlds like Europa or Enceladus are situated below

thick icy crusts. In fact, a recent study suggests that Europa’s ice shell

may still be growing (Shibley and Goodman, 2024).

While Ground-Penetrating-Radar is useful to better understand

the icy shell and underlying oceans of Solar System bodies (e.g.,

Heggyetal., 2017), yet nobody drilled or melted through an

icy moon’s shell to gather in situ information from the ocean

water. Technology to penetrate the ice is, hence, a key technology

for future missions. Thermal melting seems to be a promising

technology to achieve this task due to its mechanical simplicity and

robustness (Dachwaldetal., 2023). Also, thermal melting probes

can be operated autonomously, and the removed ice is transported

as meltwater to the back of the thermal drill. In contrast, mechanical

drilling requires less energy (Rinaldietal., 1990), but it faces the

issue that cut ice chips must be mechanically transported to the back

of a mechanical drill. Whatever penetration method would be used,

considerable infrastructure on the surface and high energy supply

will be required (Dachwaldetal., 2020).

The discovery of a plume at the south pole of Enceladus

that is sourced from a liquid water ocean in the early 2000s

Frontiers in Astronomy and Space Sciences 07 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

(Hansenetal., 2006;Porcoetal., 2006) inspired the development

of space mission concepts that include thermal melting probes

(Konstantinidisetal., 2015) and the development of new types

of melting probes (Dachwaldetal., 2020). Activities in Germany

are mainly organized within the Explorer Initiatives led by the

DLR (Section 2.1) and include the EnEx-IceMole concept that

is maneuverable due to its ice screw and differential heating

(Dachwaldetal., 2014;Kowalskietal., 2016;Baaderetal., 2024),

tiny laboratory scale probes (Baaderetal., 2016), and small helper

probes for localization (Weinstocketal., 2021). Another probe is

the large TRIPLE-IceCraft (Heinenetal., 2021; see Section 2.1)

that will allow to carry small autonomous underwater vehicles

(TRIPLE-nanoAUV) as a payload (Waldmann and Funke, 2020).

To describe the trajectories of such probes, modeling efforts are

ongoing (Schüller and Kowalski, 2019;Boxbergetal., 2023). A

major success was the use of the EnEx-IceMole to retrieve clean

samples from a water reservoir that feeds the Blood Falls at Taylor

Glacier in Antarctica in November 2014 (Kowalskietal., 2016;

Lyonsetal., 2019;Mikuckietal., 2023). However, the probe only

melted through about 17m of ice to reach the subglacial water.

Although the thicknesses of the ice layers on top of the icy ocean

worlds are not yet well constrained, it is very likely that melting

probes must overcome ice layers of several kilometers. Therefore,

current developments like the TRIPLE-IceCraft are focusing on

increasing the range and the level of autonomy of such melting

probes and establishing a standardized interface to enable an easy

integration of arbitrary scientific payloads or sensors. A first polar

test of the TRIPLE-IceCraft was performed on the shelf-ice close to

the German Neumayer Station III in Antarctica in 2023. One of the

main goals of the current TRIPLE project (Figure2) is to develop a

melting probe thatis able to penetrate ice with a thickness of 3–4km,

which is the maximum thickness available in analogue missions

on Earth, at Dome C in Antarctica. Within the same project, the

nanoAUV is developed for autonomous investigation of subglacial

water reservoirs(Waldmann and Funke, 2020). Tests in partly frozen

lakes and below shelf-ice are planned.

Recent improvements in onboard computing capacities

and power storage used within AUVs is allowing far more

detailed studies of environmental conditions and flora and fauna

distributions within the oceans of Earth and beneath the permanent

ice caps of both poles. Societal interest in global environmental

changes is driving some of these developments (Benwayetal., 2019).

There is also industrial interest in studying remote, high pressure

and variable temperature locations such as deep-sea polymetallic

nodule fields and hydrothermal provinces. The application of

these sensor systems into high pressure platforms (both automated

and tethered) for use in the underice environments is ongoing.

Permanent underice monitoring systems such as the F/Photometric

Robotic Atmospheric Monitor (FRAM) observatory network

combines traditional “Conductivity, Temperature and Depth”

sensors, cameras and direct sampling with these new systems to

inform on life below the ice – from the microscopic bacterial life

to megafauna – as well as to monitor the ongoing effects of climate

change in these underice environments.

Promising techniques for in situ analysis of the water ice and

accompanying compounds include spectroscopic techniques, such

as Laser Induced Breakdown Spectroscopy (LIBS) and Raman

spectroscopy. Both methods rely on the use of a laser and detect

the light of a laser-induced micro plasma for elemental analysis

(LIBS) or inelastically backscattered laser light for information

about molecules and lattices (Raman). They are thus greatly

complementary in giving information about the elemental and

molecular compositions of targeted samples. Both methods have

the advantage of requiring only optical access to the target

of interest with rapid data acquisition and are developed at

DLR with a focus on extraterrestrial applications including the

analysis of ices (e.g., Pavlovetal., 2011;Schröderetal., 2013;

Böttgeretal., 2017;Hagelschueretal., 2022). Salts as well as other

inorganic compounds, minerals, but also organics and complex

biomolecules can be detected and identified, even after space

exposure (Baquéetal., 2022). The instruments could serve as

payload for robots investigating the surface of an icy moon

or be integrated into systems exploring the subsurface. For

example, the Raman spectrometer RAX that was developed for

the small Martian Moons eXploration (MMX) rover weighs only

1.5kg in a volume of about 10dm3(Hagelschueretal., 2022)

and LIBS instruments of similar weight are currently under

development (Rapinetal., 2023).

4 Analogues, experimental and

numerical simulations in the field,

laboratory, and space

4.1 Field analogues

Cassini’s measurements revealed geochemical evidence for

hydrothermal vents at Enceladus’s ocean floor (Hsuetal., 2015;

Waiteetal., 2017). Terrestrial analogues sites for extraterrestrial

hydrothermal systems include deep sea vents around mid-ocean

ridges (e.g., Lost City in the Atlantic Ocean; Kelleyetal., 2005), arcs

(e.g., Tonga-Kermadec and Le Havre-Lau back arc system; Smith

andPrice,2006), and hotspotsin volcanicactive areas(e.g., Iceland).

The icy shells of several icy satellites, such as Europa,

Enceladus and Ganymede are heavily affected by brittle and ductile

deformation (e.g., Collinsetal., 2010). The analysis of the resulting

structural patterns is essential for understanding the driving forces,

such as tidally-induced stresses (Tuftsetal., 1991;Hoppaetal.,

2000). Terrestrial analogues for tectonic deformation of ice volumes

support the study of icy satellites and include mountain glaciers, ice

caps, and marine ice shelves (e.g., Blankenship and Morse, 2004). Of

particular interest are faults and fractures as pathways for ascending

fluids which could deliver biosignatures from liquid water reservoirs

within the icy shells to the surface to make these signatures available

for spacecraft analysis.

The surfaces of icy ocean worlds are exposed to high doses of

radiation (Cassidyetal., 2021). The epitome of this is the tidally

locked moon Europa, where the leading and trailing hemispheres

of the moon present stark contrast due to the differences in surface

irradiation. Terrestrial analogues to icy moon’s surfaces include the

Greenland Ice Sheet, maritime and continental Antarctica (e.g.,

McMurdo Ice Shelf, Deception island and the South Pole) and

altitude glaciers found in several mountain ranges (e.g., Southern

Ice Field in Patagonia and Andean or Himalayan glaciers).

The interaction between ice and the waterbed can be studied

through terrestrial analogue sites. Subglacial lakes such as Lake

Frontiers in Astronomy and Space Sciences 08 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

Untersee (Eastern Antarctica) present anoxic, methane rich,

stratified waters. Similar lakes, such as Lake Vida (McMurdo Dry

Valleys) or Lake Vostok (East Antarctic ice sheet) are also considered

important analogues. Lastly, Gypsum Hill Springs in Axel Heiberg

Island (Canadian Arctic) is adjacent to highly saline ice, rich in

perennial saline springs (Heldmannetal., 2005), and is relevant for

studying both Enceladus and Europa.

Field tests are not only valuable for testing drilling and melting

probes, such as the TRIPLE-IceCraft (see Sections 2.1,3), but also

for studying the compositions, including organics and microbes,

of sites analogous to icy ocean worlds. The Planetary Sciences &

RemoteSensing group atFreieUniversitätBerlinrecentlyconducted

icy moon analogue research in coastal Antarctica, with a field

campaign at the beginning of 2024 (HortalSánchezetal., 2024)

carried out in collaboration with the Centro de Astrobiología

in Spain and the Instituto Antártico Uruguayo. The goal was

to retrieve icy samples in King George Island, in the South

Shetlands islands in the Antarctica peninsula. Samples were

collected in the Southwestern region of Collins Glacier (a.k.a

Bellingshausen Glacier), at four sampling points: by the seaside, at

the dome, by the land front and in cryoconite pockets. Cryoconite

pockets are of special interest due to their high organic content.

They usually form during summer due to the lower albedo of

the accumulated dark dust (i.e., soot, ash and rock particles),

and the resulting higher temperature that melts the glacier ice

directly under it. Alpine and McMurdo Dry Valley glaciers with

cryoconite surfaces and holes have proven to be unique niches

for psychrophiles (Porazinskaetal., 2004;Margesinetal., 2012).

Deposition of micrometeorites on the surface of icy moons may

create similar conditions for putative life-forms ejected from the

subsurface oceans of these moons.

At the sampling site by the seaside, deposition of ocean-

borne aerosols is expected. The action of wind on the sea

around polar regions on Earth creates sub-micron aerosols:

ice particles that are organic-rich and salt-poor (Burrowsetal.,

2014). These organic-laden ice particles are similar in

composition to the organic rich Type II ice grains found in

Enceladus plume (Postbergetal., 2018). The deposition of these

ice particles on the glacier’s surface and subsequent sampling

presents an excellent analogue for the study of ice grains from icy

ocean worlds.

Sampling carried out at the dome of the glacier as well as

by the land front could present interesting cases for organic-

poor ices and organic-rich ices, respectively, the latter having

a bigger organic input from non-microbial species (e.g., algae).

This expected difference in concentration of the target analyte

allows further assessment on the limitations and capabilities of

spaceborne instruments on board future space missions to icy

ocean moons.

The collected samples include both deep ice cores (Figure4)

and surface ice. They will be analyzed with a range of

analytical techniques to evaluate the organic content and

presence of biosignatures that could be detected with spaceborne

instrumentationonboard missionstoicymoons(e.g.,Klenneretal.,

2019). A detailed comparison of the data obtained by the different

analytical techniqueswill provide analogue data for the detections of

biosignatures by combining several instruments onboard spacecraft.

FIGURE 4

Ice core collected at the dome of Collins glacier by the Planetary

Sciences & Remote Sensing group at Freie Universität Berlin at the

beginning of 2024.

4.2 Experimental studies

Laboratory-based simulations complement our understanding

of icy ocean worlds, their interaction with different radiation

fields and allow us to examine specific chemical reaction pathways

in much more detail. Some experimental setups are based on

an ultra-high vacuum (UHV) chamber that is equipped with

a cryostat and linked to radiation sources that provide X-

rays, UV photons, or particle radiation. Ice analog samples are

created via background condensation of gas-phase molecules on

suitable substrates. For example, one such facility is operated at

Freie Universität Berlin, where various ice mixtures on top of

organic layers are irradiated using either an electron gun, a solar

simulator, or both simultaneously. Detailed analysis of the samples is

performed using Fourier-transform infrared (FT-IR) transmission

spectroscopy and mass spectrometry, which are available both

during the irradiation process and the warming-up process.

Another setup, newly built at the Planetary Spectroscopy

Laboratory at DLR Berlin, aims at performing bi-directional

reflectance measurements under cryogenic conditions to support

current and upcoming missions to the outer Solar System, including

ESA’s JUICE and NASA’s Lucy. The setup allows for measurements

from UV to far infrared for up to four samples at temperatures lower

than −150°C under vacuum down to 10−6hPa (Helbertetal., 2023).

A setup (PI Nozair Khawaja) is being designed that can simulate

the conditions in the only known extraterrestrial hydrothermal vent

system, i.e., Enceladus seafloor (Figure5). A detailed hydrothermal

experimental plan is made to process several species in this reactor

to investigate the effects of hydrothermal processing of compounds

before incorporation in ice grains (Khawajaetal., 2024a). DAbG

members at US institutionsare involved in experimental studies that

address the formation of these ice grains (Klenneretal., 2024a) as

well as fractionation processes occurring upon eruption of an ocean

world plume (Fiferetal., 2024).

The analysis of ice grains in space can be achieved by impact

ionization mass spectrometers, such as SUDA on board Europa

Clipper (Kempfetal., 2024). However, a detailed analysis of ice

Frontiers in Astronomy and Space Sciences 09 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

FIGURE 5

Experimental hydrothermal reactor used to simulate the conditions in Enceladus’s interior. More information about this setup can be found in Khawaja

et al. (2024a)

grain mass spectra requires laser-based analogue experiments

conducted at Freie Universität Berlin (Klenneretal., 2019;2022;

Sanderinketal., 2023). This approach has successfully been used

to analyze ice grain mass spectra recorded by Cassini (e.g.,

Postbergetal., 2018;Postbergetal., 2023) and predict mass spectra

of ice grains containing molecules essential for the emergence of

water- and carbon-based life, such as amino acids (Klenneretal.,

2020a). Mass spectral data from impact ionization instruments

can also be simulated using dust accelerators in a laboratory

environment or quantum chemistry techniques in computer

simulations (O’Sullivan et al., 2024).

However, the duration of particle exposure to the space

environment before being analyzed can have an influence on their

composition and on the preservation and detectability of complex

organic molecules as potential traces of life. Laboratory-based

simulations of certain space factors are necessary but generally not

enough to fully recreate a complex space environment, especially in

terms of radiation. Thus, several exposure experiments involving

space platforms have been conducted by space agencies since

humanity’s presence in Low Earth Orbit (LEO) and beyond

(Hornecketal., 2010). Among the latest ones, ESA’s EXPOSE

platform allowed a long-term exposure (12–18 months) in LEO

of biological and chemical samples outside the International

Space Station (ISS). It completed its third and final mission

called EXPOSE-R2 in 2016 (Rabbowetal., 2017). New active

and passive exposure experiments in LEO are currently being

developed and prepared for flight by ESA and partners: the

new payload EXPO on the Bartholomeo platform will include

several experiments dedicated in part to the exposure of ice

particles and their components: BioSigN (BioSignatures and

habitable Niches), IceCold, OREOcube (ORganics Exposure

in Orbit cube) and ExoCube (Exposure of organics/organisms

cube). On these platforms, in situ analytical methods (including

spectroscopy) are crucial tools for understanding photochemical

and radiation-biological processes for studying organics and

potential biosignatures. Simulating icy moon conditions through

space experiments presents a challenge, particularly in maintaining

low temperatures throughout the space exposure phase. New

concepts for low-temperature platforms that enable irradiation and

exposure of samples to space conditions exist (Cottinetal., 2022)

but face implementation challenges.

4.3 Numerical simulations

Another important aspect in assessing the habitability of icy

ocean worlds is to gain further understanding of the subsurface

environment on a large scale. The cryo-subsurface environment

includes the uppermost ice crust, the ocean as well as high-

pressure ice layers. Whether an ocean or high-pressure ice layers

are likely to occur depends on the individual icy moon (see

review in Soderlundetal., 2020). Numerical models predicting the

interior structure (e.g., Sohletal., 2002) are based on observational

constraints (e.g., the bodies mass, the moment of inertia factor or

the tidal love number) and high-pressure experiments to investigate

the material properties at high pressures and temperatures. The

presence of liquids in these layers and the exchange of heat and

material between them to address the overall habitability is subject

to ongoing studies.

The uppermost ice crust may contain salt-rich liquids (brine) in

the form of, for example, small subsurface lakes (e.g., Schmidtetal.,

2011), cracks (e.g., Rudolphetal., 2022) or interstitial water

at grain boundaries (e.g., Wolfenbargeretal., 2022). Salt is an

essential ingredient in these cryo-environments as it efficiently

decreases the melting temperature and thus prevents liquids

from freezing in these otherwise extremely cold conditions.

Liquid inclusions may originate from the ocean beneath the ice

crust (e.g., Soderlundetal., 2020).

Frontiers in Astronomy and Space Sciences 10 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

Recent modeling attempts address the uptake of salt-enriched

liquids at the ice-ocean interface by investigating the physics of a

mushy layer between the (mainly) solid ice crust and the ocean

(Buffoetal., 2020;Buffoetal., 2021). A connected and emerging

field of research is the interplay of the dynamics of the meso-

scale mushy layer and the large-scale ice crust. Coupled models,

developed by DLR scientists, are able to tell whether liquids trapped

at the ice-ocean interface can move within the ice crust and remain

liquid over longer periods of time (Myrs to Gyrs; Rückriemen-

Bezetal., 2023). Other ways to create liquids are local melting of

the ice crust due to heat sources such as tidal heating in the case

of Europa (Sotinetal., 2009) and Enceladus (Spencer and Nimmo,

2013) or heating by impacts (Cox and Bauer, 2015). In both cases,

large-scale models of the ice shell - being developed now - can

investigate how the associated heat anomalies and liquid fractions

are evolving, which ultimately provides an estimate of the lifecycle

of habitable niches in the ice shell.

The ocean is of particular interest when the ocean floor is

expected to be in direct contact with rocks (see Sections4.1,5). The

suspected aqueous alteration of silicates is thought to be responsible

for most of the ocean’s salinity and organic molecules (Zolotov

and Shock, 2001;Zolotov and Kargel, 2009). Fluid motions in the

ocean influence the degree of mixing of these salty and organic

compounds, and thus the distribution of chemical and thermal

gradients. Numerical studies of ocean dynamics cover topics

such as global circulation (e.g., Soderlund, 2019;Terra-Novaetal.,

2023) and ocean tides (e.g., Matsuyamaetal., 2018;Rovira-

Navarroetal., 2019).

Especially for larger icy moons such as Ganymede, Callisto

or Titan, high-pressure ice layers may occur above the rocky

core of the moons effectively shielding any potential ocean from

being in direct contact with rocks (Journauxetal., 2020). In

these scenarios it is not immediately clear if the ocean can be

continuously fueled with salts and organics, which is crucial for

creatingahabitable environment. Aprimary interestis thusstudying

the transport of heat and material across the high-pressure ice

layers. Recent models have investigated whether (and at which

rate) liquids emerging at the interface between the high-pressure

ice and the rocky core are released into the overlying ocean

(Chobletetal., 2017;Kalousová and Sotin, 2018;Lebecetal., 2024).

Phenomena like magmatic volcanism originating from the rocky

core and its effect on the ocean as well as the high-pressure ice

layers have only recently come into focus (Bland and Elder, 2022;

Kervazoetal., 2022).

Currently, in Germany, individual modeling efforts focus mostly

on Europa and Enceladus. These efforts are being undertaken at the

Freie Universität Berlin (e.g., Matteonietal., 2023;Schmidtetal.,

2024), University of Münster (e.g., Wongetal., 2022), University

of Braunschweig (e.g., Gundlachetal., 2018), and at the DLR

in Berlin (e.g., Plesaetal., 2024) in collaboration with RWTH

Aachen (Rückriemen-Bezetal., 2022) and with the University

of Münster (Holmetal., 2024). Future research needs to combine

different modeling strategies to tackle overarching research topics

that may be addressed in large collaborative projects. A crucial

part of future planetary ocean models should be the influence of

boundaries (ice shell at the top, rocky core/high-pressure ice at the

bottom) on the ocean and vice versa.

5 Organics and detection of

biosignatures

Besides the presence of liquid water, chemical disequilibria,

available energy and organic molecules are important conditions

and ingredients of life as we know it. Water is an excellent medium

to initiate and facilitate biochemical reactions as well as nutrient

transport, important for originating and sustaining life. Therefore,

the discovery of subsurface liquid water oceans on icy moons

triggeredthe searchfororganicsandbiosignaturesinrecent decades.

DAbG members are involved in these efforts through various

international projects and play a significant role in developing a

systematic way to life detection by combining laboratory and field

work with Low Earth Orbit (LEO) experiments (deVera, 2019;

deVeraetal., 2019;Baquéetal., 2022).

Organic and inorganic material can be leached from a rocky

core into the subsurface ocean through water-mineral interactions

at the seafloor. On Enceladus, such interactions may even take

place throughout the whole rocky interior because of the relatively

high porosity of the core (Kisvárdaietal., 2023). Further heat

and chemical diversity could be provided through serpentinization

reactions at the seafloor (e.g., Farkas-Takácsetal., 2022).

Active cryovolcanism on Enceladus (Porcoetal., 2006), and

potentially Europa (e.g., Sparksetal., 2017;Bradáketal., 2023),

providea meansofmaking materialfromthesubsurface waterocean

accessiblefor in situ analysesbyspacecraft.On Titan, organic surface

material may be delivered to the subsurface water ocean through

impact cratering (Neishetal., 2024).

With the instruments already sent to icy moons (e.g.,

Sramaetal., 2004), a large variety of organic compounds could

be found in Enceladus’s ocean by the analysis of mass spectra

of emitted ice grains (Postbergetal., 2018;Khawajaetal., 2019).

Some of these organics could potentially act as amino acid

precursors. Cassini’s data recently revealed more organics emerging

from the subsurface ocean of Enceladus. These organics suggest

an alternative pathway for organic synthesis that could lead to

the formation of more complex organics, such as Polycyclic

Aromatic Hydrocarbons (PAHSs) (Khawajaetal., 2024b). Because

of these discoveries, many laboratory efforts are ongoing to

better understand the processing and detectability of organics,

including potential biosignatures (Malaterreetal., 2023), on icy

ocean worlds (e.g., Klenneretal., 2020a;Klenneretal., 2020b;

Napoleonietal., 2023a;Napoleonietal., 2023b;Dannenmannetal.,

2023;Khawajaetal., 2023). The results of these experiments show

that many organics and biosignatures, including biotic fatty acid

abundance patterns or DNA molecules, will be identifiable with

future spaceborne instruments, such as SUDA (Kempfetal., 2024)

or the High Ice Flux Instrument (Mousisetal., 2022), thereby

advancing the search for life in the Solar System. Moreover,

methods are being developed to combine data from different

analytical techniques in a complementary way to elucidate

the composition of unknown organic species emerging from

extraterrestrial oceans (Khawajaetal., 2022). Such laboratory

investigations are primordial to guide future space missions and

make recommendations for the detection of organic molecules or

evenlife.TheserecommendationsareparticularlyrelevanttoEuropa

Clipper (Pappalardoetal., 2024) or potential future Enceladus

missions (Cableetal., 2021;Mousisetal., 2022).

Frontiers in Astronomy and Space Sciences 11 frontiersin.org

Related document tools

Review originality and document trust

Plag helps review text similarity and possible source overlap. Identific adds another layer when trust and verification matter. They are useful when quality and trust matter.

plag.ai

Klenner etal. 10.3389/fspas.2024.1422898

In addition to terrestrial laboratory calibrations, experiments

conducted on the International Space Station (ISS) involve

organic molecules that are exposed to cosmic radiation. Several

DAbG members are actively planning these experiments to

support the exploration of Enceladus, Europa, Mars and

beyond (e.g., Elsaesseretal., 2023).

6 Extremophile research

Icy ocean worlds present a potential abode for habitability, but

their environments are challenging for the origin and persistence

of life. Jupiter’s icy moons, such as Europa and Ganymede but

also Saturn’s satellite Enceladus are subject to huge amounts of

radiation on their surface, which could alter potential biomolecules

that originate from their interiors. Not much is known about

the environment within the subsurfaces of icy moons, but sub-

zero temperatures, high pressure, low light levels, and probably

high salt concentration beneath the ice crusts could be inferred

(e.g., Marusiaketal., 2021). The thriving microbial life discovered

in some of the most extreme environments on Earth serves as

a potential analogue for habitats on these moons, particularly

deep-sea hydrothermal vents (McClimentetal., 2006) and zones of

accumulated sea water beneath and within Antarctic ice (Garrison,

1991), suggesting that life may also be able to exist under similar

conditions in the subsurface oceans of some of the icy moons

(Russeletal., 2017;Martin and McMinn, 2018;Weberetal., 2023).

Hypothetical models of organisms that might live under the ice

crusts of the icy moons have been advanced (e.g., Schulze-Makuch

and Irwin, 2002). However, a special emphasis has been the

study of polyextremophiles, which are adapted to thrive under

multiple environmental stresses and serve as useful models for

studying the limits of life. They provide valuable insights into

the potential habitability of extreme environments, on both Earth

and beyond (Thombreetal., 2020). These environments are also

of special interest to the study of the origin of life. Can life

originate under a hydrothermal vent scenario as has been suggested

by multiple authors for Earth (e.g., Martinetal., 2008) or are

land areas required for an origin of life as suggested by other

authors (e.g., Schulze-Makuch and Irwin, 2018;Damer and Deamer,

2020;Toner and Catling, 2020;Haasetal., 2024)? Extremophile

research is a rapidly growing field involving DAbG members from

diverse disciplines, including microbiology, biochemistry, geology,

and planetary sciences (e.g., Klenneretal., 2024b).

Recent advancements in technology have significantly improved

our ability to study extremophiles (e.g., Caro-Astorgaetal.,

2024). Innovations in deep-sea robotics, high-pressure cultivation

techniques, and advanced/new molecular biology tools are changing

how we approach this research. These technologies not only allow

for a deeper understanding of extremophiles but also equip us with

tools for the search for potential life in space, especially on icy

ocean moons.

The study of extremophiles is essential in astrobiology. By

studying and comprehending how life adapts and thrives in

Earth’s most extreme conditions, we can better speculate about

life’s potential beyond Earth. This knowledge influences the

design of future space missions, including the development of

instruments capable of detecting life (e.g., Klenneretal., 2024b) and

understanding its biochemistry.

7 Cleanliness and decontamination

controls

In exploring icy ocean moons, we also face ethical issues

and challenges. One major concern is the possibility of

contaminating other celestial bodies with Earth’s life forms (forward

contamination) or bringing extraterrestrial organisms to Earth

(backward contamination; e.g., Rettbergetal., 2019). This situation

requires strict procedures to ensure a balance between scientific

exploration and protecting potential ecosystems. The equipment

that may touch pristine icy moon environments must be cleaned

and verified. Applying a rigorous witness plan, for example, by

using witness plates, provides a possibility to passively record the

contamination level during the fabrication or testing of spacecraft

instrumentation (e.g., Weissbrodtetal., 1994).

Novel thermoelectric melt probes such as the EnEx-

IceMole, developed with funding from the German Federal

Ministry for Economic Affairs and Energy (BMWi) can

be specifically designed and optimized for (self)cleaning

(Dachwaldetal., 2014;Kowalskietal., 2016). They utilize no fuel,

have a significantly smaller logistical footprint, and therefore offer

potentially cleaner means of accessing the subglacial environment

than many alternative ice penetration approaches.

The measures required for mitigation of contamination risks

can be broadly divided into two groups, that should go hand-

in-hand: (I) a complex of assays for contamination monitoring

and assessment and (II) a set of procedures aimed at biological

and chemical burden reduction. In terms of biological or organic

contamination, celestial environments are under protection

by the guiding principles of the Planetary Protection Policy

(Kmineketal., 2020).

Many aspects and components of the Planetary Protection

Policy are reflected in further official standards regulating

exploration of polar terrestrial regions. This includes the Protocol

on Environmental Protection within the Antarctic Treaty, and

the Code of Conduct (CoC) for the Exploration and Research

of Subglacial Aquatic Environments (DoranundVincent, 2011;

SiegertundKennicutt, 2018). The principles set in both these

documents also were applied in the Clean Access Plan for the EnEx

field tests performed in Antarctica (Mikuckietal., 2023).

The tasks and recommendations regarding contamination

management and control, published in the abovementioned

documents, are derived from the necessity to reduce the number

of cells and biological molecules on the instruments that enter

(sub)glacial environments. Efficient biological and chemical

burden reduction has required developments of multiple-step

procedures for each hardware component. Usually, sampling

equipment is sterilized before its transportation to the application

site. However, this approach does not prevent contamination

appearing shortly after the mission begins, for instance, if the ice-

melting probe must penetrate contaminated upper ice layers on

its way to the subglacial locations of interest. In this situation,

two action classes must be defined: (a) pre- and inter-mission

hardware decontamination in the stationary laboratory conditions

Frontiers in Astronomy and Space Sciences 12 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

and (b) in situ measures and protocols applied during the

(sub)glacial exploration. The actions in the first group (a) can

be designed very flexibly and use numerous classical disinfection

and decontamination methods, combined and applied in a

consecutive way. In addition to cleaning with various detergents and

organic solvents, physical removal of bioburden can be assisted by

autoclaving, dry heat, exposure of surfaces to ozone, ethylene oxide,

ultraviolet or gamma radiation, gas plasmas or hydrogen peroxide

(Rummel and Pugel, 2019).

The in situ decontamination (b) is especially important

when multiple independent sampling acts have to be performed

within the same deployment, without return to the laboratory.

Main requirements for efficient in situ chemical decontamination

in glacial environments are: high killing rate and activity

against a broad range of microorganisms (spores, fungi, viruses,

small insects, etc.), fast decomposing, environmentally friendly

end products, easy handling, good solubility in water at

any temperatures, good penetration ability, activity in cold

environments, easy storage and easy application. Several successful

decontamination protocols are developed and validated, for

example, in the laboratories at FH Aachen University of Applied

Sciences, using specially designed compositions based on 3%–5%

(v/v) hydrogen peroxide and 3% (v/v) sodium hypochlorite

(Leimeaetal., 2010).

8 Relevance to systems on Earth

Considering the challenging work for realizing missions

to the outer Solar System and to investigate particularly the

habitable and potentially inhabited icy ocean worlds around Jupiter

and Saturn, it is clear that the technology developments and

realization of such missions have also a significant impact on

the realization of tools necessary to explore environments on

Earth (see also Section4.1). An excellent side effect of this fact is

the collaboration of engineers, natural scientists and information

scientists from the three main research fields, such as polar

research, ocean/deep sea research and space research, who finally

are able to use different facilities and develop instruments for

society relevant topics such as climate change studies, economic

energy use, exploration of the ocean, exploration of the remote

polar areas and also the exploration of space for finding new

resources.

The oceans of Earth are far more dynamic and varied than

is commonly assumed (Olbersetal., 2012), with the ice-covered

regions doubly so. Taking the Arctic and Antarctic in turn, the

Arctic ocean is in general an area with reasonably thin ice cover

(several meters thick the general maximum thickness) that waxes

and wanes in coverage throughout the year, with the central high

Arctic permanently covered in moving sea ice (Kwok, 2018). The

recent Multidisciplinary drifting Observatory for the Study of Arctic

Climate (MOSAiC) expedition locked the German Polarstern

research icebreaker of the Alfred Wegener Institute for Polar

and Marine Research (AWI) in Bremerhaven into this moving

ice to monitor firsthand the highly variable under and above

ice environmental conditions taking place throughout the polar

summer and polar night (Nicolausetal., 2022). Below the ice, the

water depth of the Arctic varies from a few centimeters at the coast

to 5,500m in the Molloy Deep. Topography is also highly variable,

with flat plains interspersed with steep hills, cliffs, seamount chains,

isolated seamounts, ridges and rises (Jakobssonetal., 2012). Of

particular interest to icy moon research may be the Gakkel Ridge,

a 4,000m and ultraslow constructive plate margin running across

the central Arctic, touching 85°N, and supporting a variety of active

hydrothermal vents at depth, each with a unique community of life

(Ramirez-Llodraetal., 2023). Shallow 1,000m–2,000m seamounts

adjacent to the ridge are 100% covered by thick, extremely slow

growing and long living sponge communities (Stratmannetal.,

2022). Other sponge communities seem to bloom in the

deeps, downstream of hydrothermal sources. Other Arctic

areas include the extended Lomonsov Ridge and numerous

isolated basins.

The Antarctic ocean contrasts with the Arctic in that it

has a continental landmass center, covered with kilometers of

glacial ice, containing many hundreds of isolated lakes of briny

waters that cannot be reached by the sunlight (Dorscheletal.,

2022). The waters around the Antarctic continent also differ from

those surrounding the Arctic. According to current knowledge,

they lack active hydrothermalism and are covered by glacial ice

of hundreds of meters thickness, which has broken from the

continent and may stay floating or grounded in the open ocean

for decades (Wesche and Dierking, 2016). Beneath this ice, which

can form hundreds of kilometers of ice tongues out over the

ocean, no life penetrates but advected nutrients support diverse

ecosystems, as new sensor equipped robotic platforms are starting

to discover (Griffithsetal., 2021).

The great variety of polar life, food sources and environmental

niches is still largely unknown. In 2021, the vast, several hundred

km square array of actively nesting icefish was discovered in one

of the more studied regions of the Weddell Sea (Purseretal.,

2022). How these complex and diverse ecosystems interact

in the underice environment can only inform icy ocean

world research.

9 Conclusion and outlook: near future

strategies

We here presented an overview about astrobiology research

related to icy ocean worlds conducted in Germany. Due to

involvements in ESA’s JUICE and NASA’s Europa Clipper,

astrobiology investigations of icy ocean worlds are getting more

and more attention within Germany and beyond. Through various

institutions, such as the German Aerospace Center or German

universities, Germany offers itself as a partner for international

collaborations in icy ocean world research and space missions. The

German Astrobiology Society represents a valuable platform for

scientists and engineers to exchange ideas and start collaborations

in icy moon research, involving international institutions, from

space mission participations to individual research at universities

and other institutions. Efforts include the development of melting

probes to melt through the outer layer of an icy ocean world as

well as instrumentation for life detection on these worlds. These

projects feed upcoming missions, such as Europa Clipper, JUICE

and potential future missions to Enceladus, Europa or any other icy

ocean world.

Frontiers in Astronomy and Space Sciences 13 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

One important aspect of icy moon research is the impact

on society through themes like climate change, biodiversity and

the exploration of new resources, as it is also supported by

the general space program strategy of the German Government.

In the near future the synergistic strategy in space exploration

will be a significant gain for science as well as for innovative

inventions for terrestrial applications and technology developments,

particularly in increasing the benefit for the human society and

the environment on our home planet Earth. Future missions to

the icy ocean worlds with their resulting exploration technologies

will provide opportunities to further support the exploration of

Earth’s oceans and polar regions and to understand the role of

these environments for the climate and the biosphere of the

whole planet.

A new way of common cooperation should be consolidated on

the long term because of its multi-useable technology and scientific

outcome. Collaborations with international institutions are key to

realizing space missions and exploiting the full potential of icy

ocean world research. Field studies beyond Germany are easier to

realize when researchers from other locations, meaning from the

field site, are involved. Biosignature detection represents another

realm in which various international institutions, particularly US

institutions, arecollaboratingwithresearchersfrom Germany. Inthe

near future, one particular focus should lie on modeling efforts to

investigate the interactions between a subsurface ocean and a rocky

core or an ice shell.

It is clear that the sequence of field investigations, lab research

and space tests should be maintained and further supported.

Synergy is key and will lead to collaborative actions as well

as to visible solutions of common problems. To get there,

politicians, national and international foundations, entrepreneurs

and stakeholders should foster this promising collaborative

interdisciplinary approach by significantly increasing their budgets

for supporting such cooperative synergistic activities, technology

developments and transfers.

Author contributions

FK: Conceptualization, Project administration, Resources,

Supervision, Visualization, Writing–original draft, Writing–review

and editing. MB: Resources, Writing–original draft, Writing–review

and editing. KB-V: Resources, Writing–original draft,

Writing–review and editing. JB: Resources, Writing–original draft,

Writing–review and editing. MB: Resources, Writing–original draft,

Writing–review and editing. BD: Resources, Writing–original draft,

Writing–review and editing. ID: Resources, Writing–original draft,

Writing–review and editing. AE: Resources, Writing–original draft,

Writing–review and editing. CE: Resources, Writing–original draft,

Writing–review and editing. OF: Resources, Writing–original draft,

Writing–review and editing. EH: Resources, Writing–original draft,

Writing–review and editing. DH: Resources, Writing–original draft,

Writing–review and editing. FH: Resources, Writing–original draft,

Writing–review and editing. LHS: Resources, Writing–original

draft, Writing–review and editing. NK: Resources, Writing–original

draft, Writing–review and editing. MN: Resources, Writing–original

draft, Writing–review and editing. A-CP: Resources,

Writing–original draft, Writing–review and editing. FP: Resources,

Writing–original draft, Writing–review and editing. AP:

Resources, Writing–original draft, Writing–review and editing.

TR-B: Resources, Writing–original draft, Writing–review and

editing. SS: Resources, Writing–original draft, Writing–review

and editing. DS-M: Resources, Writing–original draft,

Writing–review and editing. SU: Resources, Writing–original

draft, Writing–review and editing. J-PdV: Conceptualization,

Project administration, Resources, Writing–original draft,

Writing–review and editing.

Funding

The author(s) declare that financial support was received

for the research, authorship, and/or publication of this article.

FK acknowledges support from the NASA Habitable Worlds

Program grant No. 80NSSC19K0311. The DLR-internal institutes

acknowledge the programmatic support in the development

proposal “IMOTEC (Icy Moons Technologievorbereitung)”.

The Institut für Bioengineering at FH Aachen acknowledges

support from German Federal Ministry of Education (BMBF)

and German Federal Research Centre for Aeronautics and Space

Research (DLR) within the grant 50RK2351C: “TRIPLELifeDetect-

Technologies for Rapid Ice Penetration and subglacial Lake

Exploration - Life Detection A holistic, technological concept to

Life Detection Missions in Extreme Cryosphere Environments.”

AE acknowledges support from the Ministry of Economics

and Energy (Projekträger Deutsches Zentrum für Luft-und

Raumfahrt, grants 50WB1623 and 50WB2023. Furthermore,

funding and support from the Forschungskomission (via

TEAMS funding) of Freie Universität Berlin is gratefully

acknowledged. FH is supported by Volkswagen Foundation and its

Freigeist Program (AE, FH).

Acknowledgments

This publication emerged in the framework of the Ocean

Worlds and Icy Moons working group of the German Astrobiology

Society (DAbG). The authors note that the institutions, missions,

and projects with German contributions to icy ocean world

astrobiology research discussed in this paper are without any claim

to completeness.

Conflict of interest

The authors declare that the research was conducted in the

absence of any commercial or financial relationships that could be

construed as a potential conflict of interest.

The author(s) declared that they were an editorial board member

of Frontiers, at the time of submission. This had no impact on the

peer review process and the final decision.

The author who is an editorial board member had no editorial

role in the present paper and also no personal relations to the editor

of this article.

Frontiers in Astronomy and Space Sciences 14 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

Publisher’s note

All claims expressed in this article are solely those of the

authors and do not necessarily represent those of their affiliated

organizations, or those of the publisher, the editors and the

reviewers. Any product that may be evaluated in this article,or claim

that may be made by its manufacturer, is not guaranteed or endorsed

by the publisher.

References

Baader, F., Boxberg, M. S., Chen, Q., Förstner, R., Kowalski, J., and Dachwald,

B. (2024). Field-test performance of an ice-melting probe in a terrestrial analogue

environment. Icarus 409, 115852. doi:10.1016/j.icarus.2023.115852

Baader, F., Dachwald, B., Espe, C., et al. (2016). Testing of a miniaturized subsurface

icecraft for an Enceladus lander mission under enceladus-like conditions. LPI Contrib.

No. 1927. Abstract #3029.

Baqué, M., Backhaus, T., Meeßen, J., Hanke, F., Böttger, U., Ramkissoon, N., et al.

(2022). Biosignature stability in space enables their use for life detection on Mars. Sci.

Adv. 8, eabn7412. doi:10.1126/sciadv.abn7412

Barabash, S., Wurz, P., Brandt, P., et al. (2013). Particle environment package (PEP).

Eur. Planet. Sci. Congr. 8, EPSC2013–709.

Barker, J. D., Sharp, M. J., and Turner, R. J. (2009). Using synchronous fluorescence

spectroscopy and principal components analysis to monitor dissolved organic matter

dynamics in a glacier system. Hydrol. Process. 23, 1487–1500. doi:10.1002/hyp.7274

Barnes, J. W., Turtle, E. P., Trainer, M. G., Lorenz, R. D., MacKenzie, S. M.,

Brinckerhoff, W. B., et al. (2021). Science goals and objectives for the dragonfly titan

rotorcraft relocatable lander. Planet. Sci. J. 2, 130. doi:10.3847/psj/abfdcf

Beauchamp, P. M., McKinnon, W., Magner, T., et al. (2009). Technologies for outer

planet missions: a companion to the outer planet assessment group (OPAG) strategic

exploration white paper.

Benway, H. M., Lorenzoni, L., White, A. E., Fiedler, B., Levine, N. M., Nicholson,

D. P., et al. (2019). Ocean time series observations of changing marine ecosystems:

an era of integration, synthesis, and societal applications. Front. Mar. Sci. 6, 393.

doi:10.3389/fmars.2019.00393

Bland, M. T., and Elder, C. M. (2022). Silicate volcanism on Europa’s seafloor

and implications for habitability. Geophys. Res. Lett. 49 (5), e2021GL096939.

doi:10.1029/2021gl096939

Blankenship, D. D., and Morse, D. L. (2004). “Earth’s ice sheets and ice shelves as an

analog for europa’s icy shell,” in Workshop on europa’s icy shell: past, present, and future.

February 6-8, Houston, Texas, abstract no.7053.

BMWK (2023). Raumfahrtstrategie der Bundesregierung, Bundesministerium für

Wirtschaft und Klimaschutz (BMWK). Berlin, 1–60.

Böttger, U., Bulat, S. A., Hanke, F., Pavlov, S. G., Greiner-Bär, M., and Hübers, H.

(2017). Identification of inorganic and organic inclusions in the subglacial antarctic

Lake Vostok ice with Raman spectroscopy. J. Raman Spectrosc. 48, 1503–1508.

doi:10.1002/jrs.5142

Boxberg, M. S., Chen, Q., Plesa, A.-C., and Kowalski, J. (2023). Ice transit and

performance analysis for cryorobotic subglacial access missions on Earth and Europa.

Astrobiology 23, 1135–1152. doi:10.1089/ast.2021.0071

Bradák, B., Kereszturi, Á., and Gomez, C. (2023). Tectonic analysis of a newly

identified putative cryovolcanic field on Europa. Adv. Space Res. 72, 4064–4073.

doi:10.1016/j.asr.2023.07.062

Buffo, J. J., Schmidt, B. E., Huber, C., and Meyer, C. (2021). Characterizing

the ice-ocean interface of icy worlds: a theoretical approach. Icarus 360, 114318.

doi:10.1016/j.icarus.2021.114318

Buffo, J. J., Schmidt, B. E., Huber, C., and Walker, C. C. (2020). Entrainment and

dynamics of ocean-derived impurities within Europa’s ice shell. J. Geophys. Res.:Planets

125, e2020JE006394. doi:10.1029/2020je006394

Burrows, S. M., Ogunro, O., Frossard, A. A., Russell, L. M., Rasch, P. J., and Elliott,

S. M. (2014). A physically based framework for modeling the organic fractionation

of sea spray aerosol from bubble film Langmuir equilibria. Atmos. Chem. Phys. 14,

13601–13629. doi:10.5194/acp-14-13601-2014

Cable, M. L., Porco, C., Glein, C. R., German, C. R., MacKenzie, S. M., Neveu,

M., et al. (2021). The Science case for a return to Enceladus. Planet. Sci. J. 2, 132.

doi:10.3847/psj/abfb7a

Caro-Astorga, J., Meyerowitz, J. T., Stork, D. A., Nattermann, U., Piszkiewicz, S.,

Vimercati, L., et al. (2024). Polyextremophile engineering: a review of organisms that

push the limits of life. Front. Microbiol. 15, 1341701. doi:10.3389/fmicb.2024.1341701

Carré, L., Henneke, G., Henry, E., Flament, D., Girard, É., and Franzetti, B.

(2024). DNA polymerization in icy moon abyssal pressure conditions. Astrobiology 24,

151–162. doi:10.1089/ast.2021.0201

Cassidy, T., Coll, P., Raulin, F., Carlson, R. W., Johnson, R. E., Loeffler, M. J., et al.

(2021). Radiolysis and photolysis of icy satellite surfaces: experiments and theory. Space

Sci. Rev. 153, 299–315. doi:10.1007/s11214-009-9625-3

Choblet, G., Tobie, G., Kalousove, K., Kalousová, K., and Grasset, O. (2017). Heat

transport in the high-pressure ice mantle of large icy moons. Icarus 285, 252–262.

doi:10.1016/j.icarus.2016.12.002

Collins, G., McKinnon, W. B., Moore, J. M., et al. (2010). “Tectonics of the outer

planet satellites,” in Planetary tectonics. Editors T. Watters, and R. Schultz (Cambridge

University Press), 264–350.

Cottin, H., Stalport, F., Grand, N., et al. (2022). “The IR-COASTER project for

astrobiology experiments oustide the International Space Station or as a payload for

6U CubeSats,” in 44th COSPAR scientific assembly abstract F3.2-0007-22.

Cox, R., and Bauer, A. W. (2015). Impact breaching of Europa’s ice:

constraints from numerical modeling. J. Geophys. Res.:Planets 120, 1708–1719.

doi:10.1002/2015je004877

Dachwald, B., Mikucki, J., Tulaczyk, S., Digel, I., Espe, C., Feldmann, M., et al. (2014).

IceMole: a maneuverable probe for clean in situ analysis and sampling of subsurface ice

and subglacial aquatic ecosystems. Ann. Glaciol. 55, 14–22. doi:10.3189/2014aog65a004

Dachwald, B.,Ulamec,S., Kowalski,J., etal. (2023).“Ice melting probes,” inHandbook

of space resources. Editors V. Badescu, K. Zacny, and Y. Bar-Cohen (Springer), 955–996.

Dachwald, B., Ulamec, S., Postberg, F., Sohl, F., de Vera, J. P., Waldmann, C., et al.

(2020). Key technologies and instrumentation for subsurface exploration of Ocean

Worlds. Space Sci. Rev. 216, 83–45. doi:10.1007/s11214-020-00707-5

Damer, B., and Deamer, D. (2020). The hot spring hypothesis for an origin of life.

Astrobiology 20, 429–452. doi:10.1089/ast.2019.2045

Dannenmann, M., Klenner, F., Bönigk, J., Pavlista, M., Napoleoni, M., Hillier, J., et al.

(2023). Toward detecting biosignatures of DNA, lipids, and metabolic intermediates

from bacteria in ice grains emitted by Enceladus and Europa. Astrobiology 23, 60–75.

doi:10.1089/ast.2022.0063

De Laurentiis, E., Buoso, S., Maurino, V., Minero, C., and Vione, D. (2013). Optical

and photochemical characterization of chromophoric dissolved organic matter from

lakes in terra nova bay, Antarctica. Evidence of considerable photoreactivity in an

extreme environment. Environ. Sci. Technol. 47, 14089–14098. doi:10.1021/es403364z

Della Corte, V., Schmitz, N., Zusi, M., et al. (2014). The JANUS camera onboard

JUICE mission for Jupiter system optical imaging. Proc. SPIE 9143, Space Telesc.

Instrum. 2014 Opt. Infrared, Millim. Wave 9143, 1062–1073. doi:10.1117/12.2056353

de Vera, J.-P., and The Life Detection Group of BIOMEX/BIOSIGN (2019). “A

systematic way to life detection: combining field, lab and space research in low Earth

orbit,” in Biosignatures for astrobiology. Advances in astrobiology and biogeophysics.

Editors B. Cavalazzi, and F. Westall (Springer), 111–122.

de Vera, J.-P., Alawi, M., Backhaus, T., Baqué, M., Billi, D., Böttger, U., et al. (2019).

Limits of life and the habitability of Mars: the ESA space experiment BIOMEX on the

ISS. Astrobiology 19, 145–157. doi:10.1089/ast.2018.1897

Doran, P. T., and Vincent, W. F. (2011). “Environmental protection and stewardship

of subglacial aquatic environments,” in Antarctic subglacial aquatic environments 192.

Editors M. J. Siegert, and I. I. M. C. Kennicutt (American Geophysical Union), 149–157.

Dorschel, B., Hehemann, L., Viquerat, S., Warnke, F., Dreutter, S., Tenberge, Y. S.,

et al. (2022). The international bathymetric chart of the southern ocean version 2. Sci.

Data 9, 275. doi:10.1038/s41597-022-01366-7

Elsaesser, A., Burr, D. J., Mabey, P., Urso, R. G., Billi, D., Cockell,

C., et al. (2023). Future space experiment platforms for astrobiology

and astrochemistry research. Microgravity 9, 43. doi:10.1038/

s41526-023-00292-1

Enya, K., Kobayashi, M., Kimura, J., Araki, H., Namiki, N., Noda, H., et al. (2022). The

Ganymede laser altimeter (GALA) for the jupiter icy moons explorer (JUICE): mission,

science, and instrumentation of its receiver modules. Adv. Space Res. 69, 2283–2304.

doi:10.1016/j.asr.2021.11.036

Farkas-Takács, A., Kiss, C., Góbi, S., and Kereszturi, Á. (2022). Serpentinization in

the thermal evolution of icy kuiper belt objects in the early solar system. Planet. Sci. J.

3, 54. doi:10.3847/psj/ac5175

Fifer, L. M., Toner, J. D., Ford, K., et al. (2024). Measuring exsolution rates of gases in a

laboratory analog for Enceladus plume formation. Eur. Sci. Congr. 17, EPSC2024–1314.

doi:10.5194/epsc2024-1314

Frazier, W., Bearden, D., Mitchell, K. L., et al. (2020). Trident: the path to Triton on a

discovery budget. IEEE Aerosp. Conf., 1–12. doi:10.1109/AERO47225.2020.9172502

Funke, O., and Horneck, G. (2018). “The search for signatures of life and habitability

on planets and moons of our solar system,” in Biological, physical and technical basics

Frontiers in Astronomy and Space Sciences 15 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

of cell engineering. Editors G. M. Artmann, A. Artmann, A. A. Zhubanova, and I. Digel

(Springer), 457–481.

Garrison, D. L. (1991). Antarctic Sea ice biota. Am. Zool. 31, 17–34.

doi:10.1093/icb/31.1.17

Goordial, J., Altshuler, I., Hindson, K., Chan-Yam, K., Marcolefas, E., and Whyte, L.

G. (2017). In situ field sequencing and life detection in remote (79°26′N) Canadian

high arctic permafrost ice wedge microbial communities. Front. Microbiol. 8, 2594.

doi:10.3389/fmicb.2017.02594

Goossens, S., van Noort, B., Mateo, A., Mazarico, E., and van der Wal, W. (2024).

A low-density ocean inside Titan inferred from Cassini data. Nat. Astron 8, 846–855.

online ahead of print. doi:10.1038/s41550-024-02253-4

Grasset, O., Dougherty, M. K., Coustenis, A., Bunce, E. J., Erd, C., Titov, D.,

et al. (2013). JUpiter ICy moons Explorer (JUICE): an ESA mission to orbit

Ganymede and to characterise the Jupiter system. Planet. Space Sci. 78, 1–21.

doi:10.1016/j.pss.2012.12.002

Griffiths, H. J., Anker, P., Linse, K., Maxwell, J., Post, A. L., Stevens, C., et al.

(2021). Breaking all the rules: the first recorded hard substrate sessile benthic

community far beneath an antarctic ice shelf. Front. Mar. Sci. 8, 76. doi:10.3389/fmars.

2021.642040

Gundlach, B., Ratte, J., Blum, J., Oesert, J., and Gorb, S. N. (2018). Sintering

and sublimation of micrometre-sized water-ice particles: the formation of surface

crusts on icy Solar System bodies. Mon. Not. R. Astron. Soc. 479, 5272–5287.

doi:10.1093/mnras/sty1839

Haas, S., Sinclair, K. P., and Catling, D. C. (2024). Biogeochemical explanations for

the world’s most phosphate-rich lake, an origin-of-life analog. Commun. Earth Environ.

5, 28. doi:10.1038/s43247-023-01192-8

Hagelschuer, T., Böttger, U., Buder, M., et al. (2022). “RAX: the Raman spectrometer

for the MMX phobos rover,” in 73rd international astronautical congress.

Hand, K. P., Phillips, C. B., Murray, A., Garvin, J. B., Maize, E. H., Gibbs, R. G., et al.

(2022). Science goals and mission architecture of the Europa lander mission concept.

Planet. Sci. J. 3, 22. doi:10.3847/psj/ac4493

Hansen, C. J., Castillo-Rogez, J., Grundy, W., Hofgartner, J. D., Martin, E. S., Mitchell,

K., et al. (2021). Triton: fascinating moon, likely ocean world, compelling destination.

Planet Sci. J. 2, 137. doi:10.3847/psj/abffd2

Hansen, C. J., Esposito, L., Stewart, A. I. F., Colwell, J., Hendrix, A., Pryor,

W., et al. (2006). Enceladus’ water vapor plume. Science 311, 1422–1425.

doi:10.1126/science.1121254

Hartkorn, O., and Saur, J. (2017). Induction signals from Callisto’s ionosphere and

their implications on a possible subsurface ocean. J. Geophys. Res.:Space Phys. 122,

677–697. doi:10.1002/2017ja024269

Heggy, E., Scabbia, G., Bruzzone, L., and Pappalardo, R. T. (2017). Radar

probing of Jovian icy moons: understanding subsurface water and structure

detectability in the JUICE and Europa missions. Icarus 285, 237–251. doi:10.1016/

j.icarus.2016.11.039

Heinen, D., Audehm, J., Becker, F., et al. (2021). The TRIPLE melting probe - an electro-

thermal drill with a forefield reconnaissance system to access subglacial lakes and oceans.

San Diego, CA, USA: OCEANS, 1–7.

Helbert, J., Lorek, A., Maturilli, A., et al. (2023). Cryogenic reflectance spectroscopy

under high vacuum conditions for outer planets exploration. Infrared Remote Sens.

Instrum. XXXI 12686, 79–85. doi:10.1117/12.2678910

Heldmann, J. L., Toon, O. B., Pollard, W. H., Mellon, M. T., Pitlick, J., McKay, C.

P., et al. (2005). Formation of Martian gullies by the action of liquid water flowing

under current Martian environmental conditions. J. Geophys. Res.:Planets 110, E05004.

doi:10.1029/2004je002261

Hildebrandt, M., Creutz, T., Wehbe, B., et al. (2022). Under-ice field tests with an

AUV in abisko/torneträsk. OCEANS 1–7. doi:10.1109/OCEANS47191.2022.9977094

Holm, A., Plesa, A.-C., Rückriemen-Bez, T., et al. (2024). Solid-state convection in

Europa’s rocky core. Eur. Sci. Congr. 17, EPSC2024–699. doi:10.5194/epsc2024-699

Hoppa, G., Greenberg, R., Tufts, B. R., Geissler, P., Phillips, C., and Milazzo,

M. (2000). Distribution of strike-slip faults on Europa. J. Geophys. Res.:Planets 105,

22617–22627. doi:10.1029/1999je001156

Horneck, G., David, M. K., and Mancinelli, R. L. (2010). Space microbiology.

Microbiol. Mol. Biol. Rev. 74, 121–156. doi:10.1128/mmbr.00016-09

Hortal Sánchez, L., Napoleoni, M., Finkel, P. L., et al. (2024). Detection of molecular

biosignatures in polar ices with mass spectrometry: implications for Europa Clipper.

Eur. Sci. Congr. 17, EPSC2024–835. doi:10.5194/epsc2024-835

Howell, S. M., and Pappalardo, R. T. (2020). NASA’s Europa Clipper-a mission to

a potentially habitable ocean world. Nat. Commun. 11, 1311. doi:10.1038/s41467-020-

15160-9

Hsu, H.-W., Postberg, F., Sekine, Y., Shibuya, T., Kempf, S., Horányi, M., et al.

(2015). Ongoing hydrothermal activities within Enceladus. Nature 519, 207–210.

doi:10.1038/nature14262

Idini, B., and Nimmo, F. (2024). Resonant stratification in titan’s global ocean. Planet.

Sci. J. 5, 15. doi:10.3847/psj/ad11ef

Jakobsson, M., Mayer, L., Coakley, B., Dowdeswell, J. A., Forbes, S., Fridman, B., et al.

(2012). The international bathymetric chart of the Arctic Ocean (IBCAO) version 3.0.

Geophys. Res. Lett. 39, L12609. doi:10.1029/2012gl052219

Journaux, B., Kalousová, K., Sotin, C., Tobie, G., Vance, S., Saur, J., et al. (2020). Large

Ocean worlds with high-pressure ices. Space Sci. Rev. 216, 7. doi:10.1007/s11214-019-

0633-7

Kalousová, K., and Sotin, C. (2018). Melting in high‐pressure ice layers of large

ocean worlds — implications for volatiles transport. Geophys. Res. Lett. 45, 8096–8103.

doi:10.1029/2018gl078889

Kelley, D. S., Karson, J. A., Fruh-Green, G. L., Yoerger, D. R., Shank, T. M., Butterfield,

D. A., et al. (2005). A serpentinite-hosted ecosystem: the Lost city hydrothermal field.

Science 307 (5714), 1428–1434. doi:10.1126/science.1102556

Kempf, S., Tucker, S., Altobelli, N., et al. (2024). SUDA: a SUrface dust analyser for

compositional mapping of the galilean moon Europa. Space Sci. Rev. in press.

Kervazo, M., Běhounková, M., Tobie, G., et al. (2022). Impact of melt accumulation

on tidal heat production in Europa’s mantle. Eur. Sci. Congr. Abstr. 16, EPSC2022–234.

doi:10.5194/epsc2022-234

Khawaja, N., Hillier, J., Klenner, F., Nölle, L., Zou, Z., Napoleoni, M., et al. (2022).

Complementary mass spectral analysis of isomeric O-bearing organic compounds

and fragmentation differences through analog techniques for spaceborne mass

spectrometers. Planet. Sci. J. 3, 254. doi:10.3847/psj/ac97ed

Khawaja, N., Hortal Sánchez, L., O’Sullivan, T. R., Bloema, J., Napoleoni, M., Klenner,

F.,et al.(2024a).Laboratory characterizationofhydrothermally processed oligopeptides

in ice grains emitted by Enceladus and Europa. Philos. Trans. R. Soc. A 382, 20230201.

doi:10.1098/rsta.2023.0201

Khawaja, N., O’Sullivan, T. R., Klenner, F., Sanchez, L. H., and Hillier, J. (2023).

Discriminating aromatic parent compounds and their derivative isomers in ice

grains from Enceladus and Europa using a laboratory analogue for spaceborne mass

spectrometers. Earth Space Sci. 10, e2022EA002807. doi:10.1029/2022ea002807

Khawaja, N.,Postberg, F., Hillier, J.,Klenner,F.,Kempf, S.,Nölle, L.,etal.(2019).Low-

mass nitrogen-oxygen-bearing, and aromatic compounds in Enceladean ice grains.

Mon. Not. R. Astron. Soc. 489, 5231–5243. doi:10.1093/mnras/stz2280

Khawaja, N.,Postberg, F., O’Sullivan, T.R.,et al.(2024b).Cassini’s newlookatorganic

material in Enceladus’ plume ice grains with CDA: implication for the habitability of

Ocean Worlds. Eur. Sci. Congr. 17, EPSC2024–1055. doi:10.5194/epsc2024-1055

Kisvárdai, I., Pál, B. D., and Kereszturi, Á. (2023). Investigating the porosity of

Enceladus. Mon. Not. R. Astron. Soc. 525, 1246–1253. doi:10.1093/mnras/stad2333

Kivelson, M. G., Khurana, K. K., Russel, C. T., Volwerk, M., Walker, R. J., and Zimmer,

C. (2000). Galileo magnetometer measurements: a stronger case for a subsurface ocean

at Europa. Science 289, 1340–1343. doi:10.1126/science.289.5483.1340

Klenner,F., Bönigk,J.,Napoleoni,M., Hillier,J.,Khawaja, N.,Olsson-Francis, K.,etal.

(2024b). How to identify cell material in a single ice grain emitted from Enceladus or

Europa. Sci. Adv. 10, eadl0849. doi:10.1126/sciadv.adl0849

Klenner, F., Fifer, L. M., Journaux, B., et al. (2024a). Toward a better understanding

of ice grain formation from Enceladus’s salty ocean. Eur. Sci. Congr. 17, EPSC2024–657.

doi:10.5194/epsc2024-657

Klenner, F., Postberg, F., Hillier, J., Khawaja, N., Cable, M. L., Abel, B., et al. (2020b).

Discriminatingabiotic andbioticfingerprintsofaminoacids andfatty acidsin icegrains

relevant to ocean worlds. Astrobiology 20, 1168–1184. doi:10.1089/ast.2019.2188

Klenner, F., Postberg, F., Hillier, J., Khawaja, N., Reviol, R., Srama, R., et al. (2019).

Analogue spectra for impact ionization mass spectra of water ice grains obtained

at different impact speeds in space. Rapid Commun. Mass Spectrom. 33, 1751–1760.

doi:10.1002/rcm.8518

Klenner, F., Postberg, F., Hillier, J., Khawaja, N., Reviol, R., Stolz, F., et al.

(2020a). Analog experiments for the identification of trace biosignatures in ice

grains from extraterrestrial ocean worlds. Astrobiology 20, 179–189. doi:10.1089/

ast.2019.2065

Klenner, F., Umair, M., Walter, S. H. G., Khawaja, N., Hillier, J., Nölle, L., et al.

(2022). Developing a laser induced liquid beam ion desorption spectral database as

reference for spaceborne mass spectrometers. Earth Space Sci. 9, e2022EA002313.

doi:10.1029/2022ea002313

Kminek, G., Hedman, N., Ammannito, E., et al. (2020). COSPAR policy on planetary

protection. Space Res. Today 208, 10–22. doi:10.1016/j.srt.2020.07.009

Konstantinidis, K., Flores Martinez, C. L., Dachwald, B., Ohndorf, A., Dykta, P.,

Bowitz, P., et al. (2015). A lander mission to probe subglacial water on Saturn’s moon

Enceladus for life. Acta Astronaut. 106, 63–89. doi:10.1016/j.actaastro.2014.09.012

Kowalski,J.,Linder,P., Zierke,S., von Wulfen, B., Clemens,J., Konstantinidis, K.,et al.

(2016). Navigation technology for exploration of glacier ice with maneuverable melting

probes. Cold Reg. Sci. Technol. 123, 53–70. doi:10.1016/j.coldregions.2015.11.006

Kowalski, J., Plesa, A.-C., Boxberg, M., et al. (2024). Compiling analysis-ready ice

data across cryosphere disciplines. European Geosciences Union General Assembly.

EGU24-21117. doi:10.5194/egusphere-egu24-21117

Kwok, R. (2018). Arctic sea ice thickness, volume, and multiyear ice coverage: losses

and coupled variability (1958–2018). Environ. Res. Lett. 13, 105005. doi:10.1088/1748-

9326/aae3ec

Frontiers in Astronomy and Space Sciences 16 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

Lebec, L., Labrosse, S., Morison, A., Bolrão, D. P., and Tackley, P. J. (2024). Effects

of salts on the exchanges through high-pressure ice layers of large ocean worlds. Icarus

412, 115966. doi:10.1016/j.icarus.2024.115966

Lebreton, J.-P., Witasse, O., Sollazzo, C., Blancquaert, T., Couzin, P., Schipper, A. M.,

et al. (2005). An overview of the descent and landing of the Huygens probe on Titan.

Nature 438, 758–764. doi:10.1038/nature04347

Lei, L., Jäggi, A., Wang, Y., et al. (2021). Gan de: a mission to search for the origins

and workings of the jupiter system. 43th COSPAR Sci. Assem. Abstract B0.7-0016-21.

Leimea, W., Artmann, G. M., Dachwald, B., et al. (2010). Feasibility of an in-situ

microbial decontamination of an ice-melting probe. Eur. Chem. Tech. J. 12, 145–150.

doi:10.18321/ectj37

Li, X., Miao, Z., Dan, C., Wu, Z., and Xia, Y. (2023). In situ Nanopore sequencing

reveals metabolic characteristics of the Qilian glacier meltwater microbiome. Environ.

Sci. Pollut. Res. 30, 84805–84813. doi:10.1007/s11356-023-28250-0

Lyons, W. B., Mikucki, J. A., German, L. A., Welch, K. A., Welch, S. A., Gardner, C.

B., et al. (2019). The geochemistry of englacial brine from Taylor Glacier, Antarctica. J.

Geophys. Res.:Biogeosciences 124, 633–648. doi:10.1029/2018jg004411

MacKenzie, S. M., Neveu, M., Davila, A. F., Lunine, J. I., Craft, K. L., Cable, M. L., et al.

(2021). The Enceladus Orbilander mission concept: balancing return and resources in

the search for life. Planet. Sci. J. 2, 77. doi:10.3847/psj/abe4da

Malaterre, C., ten Kate, I. L., Baqué, M., Debaille, V., Grenfell, J. L., Javaux, E. J.,

et al. (2023). Is there such as thing as a biosignature? Astrobiology 23, 1213–1227.

doi:10.1089/ast.2023.0042

Margesin, R., Schumann, P., Zhang, D.-C., Redzic, M., Zhou, Y. G., Liu, H. C.,

et al. (2012). Arthrobacter cryoconiti sp. nov., a psychrophilic bacterium isolated

from alpine glacier cryoconite. Int. J. Syst. Evol. Microbiol. 62, 397–402. doi:10.1099/

ijs.0.031138-0

Martin, A., and McMinn, A. (2018). Sea ice, extremophiles and life on extra-

terrestrial ocean worlds. Int. J. Astrobiol. 17, 1–16. doi:10.1017/s1473550416000483

Martin, W., Baross, J., Kelley, D., and Russell, M. J. (2008). Hydrothermal vents and

the origin of life. Nat. Rev. Microbiol. 6, 805–814. doi:10.1038/nrmicro1991

Martins, Z., Bunce, E., Grasset, O., et al. (2024). Report of the Expert Committee for

the Large-class mission in ESA’s Voyage 2050 plan covering the science theme “Moons

of the Giant Planets”. Moons Giant Planets, 1–45.

Marusiak, A. G., Vance, S., Panning, M. P., Běhounková, M., Byrne, P. K., Choblet,

G., et al. (2021). Exploration of icy Ocean Worlds using geophysical approaches. Planet.

Sci. J. 2, 150. doi:10.3847/psj/ac1272

Matsuyama, I., Beuthe, M., Hay, HCFC, Nimmo, F., and Kamata, S. (2018).

Ocean tidal heating in icy satellites with solid shells. Icarus 312, 208–230.

doi:10.1016/j.icarus.2018.04.013

Matteoni, P., Neesemann, A., Jaumann, R., Hillier, J., and Postberg, F. (2023). Ménec

fossae on Europa: a strike‐slip tectonics origin above a possible shallow water reservoir.

J. Geophys. Res.:Planets 128, e2022JE007623. doi:10.1029/2022je007623

McCliment, E. A., Voglesonger, K. M., O’Day, P. A., Dunn, E. E., Holloway, J.

R., and Cary, S. C. (2006). Colonization of nascent, deep-sea hydrothermal vents

by a novel Archaeal and Nanoarchaeal assemblage. Environ. Microbiol. 8, 114–125.

doi:10.1111/j.1462-2920.2005.00874.x

Mikucki, J. A., Schuler, C. G., Digel, I., Kowalski, J., Tuttle, M., Chua, M., et al.

(2023). Field-based planetary protection operations for melt probes: validation of clean

access into the Blood Falls, Antarctica, englacial ecosystem. Astrobiology 23, 1165–1178.

doi:10.1089/ast.2021.0102

Mousis, O., Bouquet, A., Langevin, Y., André, N., Boithias, H., Durry, G.,

et al. (2022). Moonraker: Enceladus multiple flyby mission. Planet. Sci. J. 3, 268.

doi:10.3847/psj/ac9c03

Mulyukin, A. L., Demkina, E. V., Manucharova, N. A., Akimov, V. N., Andersen, D.,

McKay, C., et al. (2014). The prokaryotic community of subglacial bottom sediments

of Antarctic Lake Untersee: detection by cultural and direct microscopic techniques.

Microbiology 83, 77–84. doi:10.1134/s0026261714020143

Nadeau, J., Lindensmith, C., Deming, J. W., Fernandez, V. I., and Stocker, R.

(2016). Microbial morphology and motility as biosignatures for outer planet missions.

Astrobiology 16, 755–774. doi:10.1089/ast.2015.1376

Napoleoni, M., Klenner, F., Hortal Sánchez, L., Khawaja, N., Hillier, J. K., Gudipati,

M. S., et al. (2023b). Mass spectrometric fingerprints of organic compounds in sulfate-

rich ice grains: implications for Europa clipper. ACS Earth Space Chem. 7, 1675–1693.

doi:10.1021/acsearthspacechem.3c00098

Napoleoni, M., Klenner, F., Khawaja, N., Hillier, J. K., and Postberg, F.

(2023a). Mass spectrometric fingerprints of organic compounds in NaCl-rich

ice grains from Europa and Enceladus. ACS Earth Space Chem. 7, 735–752.

doi:10.1021/acsearthspacechem.2c00342

National Academies of Sciences, Engineering, and Medicine (2023). Origins, worlds,

and life: a decadal strategy for planetary science and astrobiology 2023-2032. Washington,

DC: The National Academies Press.

Neish, C., Malaska, M. J., Sorin, C., Lopes, R. M., Nixon, C. A., Affholder, A., et al.

(2024). Organic input to titan’s subsurface ocean through impact cratering. Astrobiology

24, 177–189. doi:10.1089/ast.2023.0055

Nicolaus, M., Perovich, D. K., Spreen, G., Granskog, M. A., von Albedyll, L.,

Angelopoulos, M., et al. (2022). Overview of the MOSAiC expedition: snow and sea

ice. Elem. Sci. Anth. 10, 000046. doi:10.1525/elementa.2021.000046

Nimmo, F., and Pappalardo, R. T. (2016). Ocean worlds in the outer solar system. J.

Geophys. Res.:Planets 121, 1378–1399. doi:10.1002/2016je005081

O’Donnell, E. C., Wadham, J. L., Lis, G. P., Tranter, M., Pickard, A. E., Stibal, M., et al.

(2016). Identification and analysis of low-molecular-weight dissolved organic carbon

in subglacial basal ice ecosystems by ion chromatography. Biogeoscience 13, 3833–3846.

doi:10.5194/bg-13-3833-2016

O’Sullivan, T. R., Bera, P. P., Khawaja, N., and Postberg, F. (2024). A computational

chemistry approach to analysing mass spectra of organic-bearing ice grains from icy

ocean worlds. Berlin, Germany: AbGradEPEC 2024.

Olbers, D., Willebrand, J., and Eden, C. (2012). Ocean dynamics. Springer Science

and Business Media, 703.

Pappalardo, R. T., Buratti, B. J., Korth, H., Senske, D. A., Blaney, D. L., Blankenship,

D. D., et al. (2024). Science overview of the Europa clipper mission. Space Sci. Rev. 220,

40. doi:10.1007/s11214-024-01070-5

Pavlov, S. G., Jessberger, E. K., Hübers, H. W., Schröder, S., Rauschenbach, I.,

Florek, S., et al. (2011). Miniaturized laser-induced plasma spectrometry for planetary

in situ analysis–The case for Jupiter’s moon Europa. Adv. Space Res. 48, 764–778.

doi:10.1016/j.asr.2010.06.034

Plesa, A.-C., Rückriemen-Bez, T., and Wünnemann, K. (2024). The role of impacts

on ice shell dynamics and surface-to-ocean exchange on Europa. Eur. Sci. Congr. 17,

EPSC2024–701. doi:10.5194/epsc2024-701

Porazinska, D. L., Fountain, A. G., Nylen, T. H., Tranter, M., Virginia, R. A., and Wall,

D. H. (2004). The biodiversity and biogeochemistry of cryoconite holes from McMurdo

Dry Valley glaciers, Antarctica. Arct. Antarct. Alp. Res. 36, 84–91. doi:10.1657/1523-

0430(2004)036[0084:tbaboc]2.0.co;2

Porco, C. C., Helfenstein, P., Thomas, P. C., Ingersoll, A. P., Wisdom, J., West, R., et al.

(2006). Cassini observes the active south Pole of Enceladus. Science 311, 1393–1401.

doi:10.1126/science.1123013

Postberg, F., Kempf, S., Schmidt, J., Brilliantov, N., Beinsen, A., Abel, B., et al. (2009).

Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus. Nature

459, 1098–1101. doi:10.1038/nature08046

Postberg, F., Khawaja, N., Abel, B., Choblet, G., Glein, C. R., Gudipati, M. S., et al.

(2018). Macromolecular organic compounds from the depths of Enceladus. Nature 558,

564–568. doi:10.1038/s41586-018-0246-4

Postberg, F., Sekine, Y., Klenner, F., Glein, C. R., Zou, Z., Abel, B., et al. (2023).

Detection of phosphates originating from Enceladus’s ocean. Nature 618, 489–493.

doi:10.1038/s41586-023-05987-9

Purser, A., Hehemann, L., Boehringer, L., Werner, E., Pineda-Metz, S. E. A., Vignes,

L., et al. (2022). The COSMUS expedition: seafloor images and acoustic bathymetric

data from the PS124 expedition to the southern Weddell Sea, Antarctica. Earth Syst.

Sci. Data 14, 3635–3648. doi:10.5194/essd-14-3635-2022

Rabbow, E., Rettberg, P., Parpart, A., Panitz, C., Schulte, W., Molter, F., et al. (2017).

EXPOSE-R2: the astrobiological ESA mission on board of the International Space

Station. Front. Microbiol. 8, 1533. doi:10.3389/fmicb.2017.01533

Ramirez-Llodra, E., Argentino, C., Baker, M., Boetius, A., Costa, C., Dahle, H., et al.

(2023). Hot vents beneath an icy ocean: the aurora vent field, Gakkel Ridge, revealed.

Oceanography 36, 6–17. doi:10.5670/oceanog.2023.103

Rapin, W., Maurice, S., Ollila, A., et al. (2023). μLIBS: a micro-scale elemenal analyser

for lightweight in situ exploration. LPI Contrib. No., 2806. Abstract #1942.

Rapley, C., Aghanim, N., Anand, M., et al. (2022). Report and recommendations to the

European space agency ministerial Council.

Rettberg, P., Antunes, A., Brucato, J., Cabezas, P., Collins, G., Haddaji, A., et al. (2019).

Biological contamination prevention for outer solar system moons of astrobiological

interest: what do we need to know? Astrobiology 19, 951–974. doi:10.1089/ast.2018.1996

Rinaldi, R. E., Koci, B. R., and Sonderup, J. M. (1990). Evaluation of deep ice core

drilling systems, 90-01. PICO TR, 1–34.

Rovira-Navarro, M., Rieutord, M., Gerkema, R., Maas, L. R., van der Wal, W., and

Vermeersen, B. (2019). Do tidally-generated inertial waves heat the subsurface oceans

of Europa and Enceladus? Icarus 321, 126–140. doi:10.1016/j.icarus.2018.11.010

Rückriemen-Bez, T.,Plesa, A.-C.,Kowalski,J., andTerschanski,B.(2022).Large-scale

dynamics and the fate of salts in Europa’s icy shell. Eur. Sci. Congr. 16, EPSC2022–689.

doi:10.5194/epsc2022-689

Rückriemen-Bez, T., Terschanski, B., Plesa, A. C., et al. (2023). Coupling ice-ocean

interface models with global-scale ice shell evolution models applied to Jovian moon

Europa. Eur. Geosci. Union General Assem. EGU23–6803. doi:10.5194/egusphere-

egu23-6803

Rudolph, M. L., Manga, M., Walker, M., and Rhoden, A. R. (2022). Cooling

crusts create concomitant cryovolcanic cracks. Geophys. Res. Lett. 49, e2021GL094421.

doi:10.1029/2021gl094421

Rummel, J. D., and Pugel, D. E. (2019). Planetary protection technologies for

planetary science instruments, spacecraft, and missions: report of the NASA Planetary

Frontiers in Astronomy and Space Sciences 17 frontiersin.org

Klenner etal. 10.3389/fspas.2024.1422898

Protection Technology Definition Team (PPTDT). Life Sci. Space Res. 23, 60–68.

doi:10.1016/j.lssr.2019.06.003

Russel, M. J., Murray, A. E., and Hand, K. P. (2017). The possible emergence of life and

differentiation of a shallow biosphere on irradiated icy worlds: the example of Europa.

Astrobiology 17, 1265–1273. doi:10.1089/ast.2016.1600

Sanderink, A., Klenner, F., Zymak, I., Žabka, J., Postberg, F., Lebreton, J. P.,

et al. (2023). OLYMPIA-LILBID: a new laboratory setup to calibrate spaceborne

hypervelocity ice grain detectors using high-resolution mass spectrometry. Anal. Chem.

95, 3621–3628. doi:10.1021/acs.analchem.2c04429

Saur, J., Duling, S., Roth, L., Jia, X., Strobel, D. F., Feldman, P. D., et al. (2015).

The search for a subsurface ocean in Ganymede with Hubble Space Telescope

observations of its auroral ovals. J. Geophys. Res. Space Phys. 120, 1715–1737.

doi:10.1002/2014ja020778

Schmidt, B. E., Blankenship, D. D., Patterson, G. W., and Schenk, P. M. (2011). Active

formation of “chaos terrain” over shallow subsurface water on Europa. Nature 479,

502–505. doi:10.1038/nature10608

Schmidt, J., Brilliantov, N., Spahn, F., and Kempf, S. (2008). Slow dust in Enceladus’

plume from condensation and wall collisions in tiger stripe fractures. Nature 451,

685–688. doi:10.1038/nature06491

Schmidt, J., Ershova, A., Postberg, F., et al. (2024). The Enceladus dust plume

from the Cassini cosmic dust analyzer. Eur. Sci. Congr. 17, EPSC2024–510.

doi:10.5194/epsc2024-510

Schröder, S., Pavlov, S. G., Rauschenbach, I., Jessberger, E., and Hübers, H. W. (2013).

Detection and identification of salts and frozen salt solutions combining laser-induced

breakdown spectroscopy and multivariate analysis methods: a study for future martian

exploration. Icarus 223, 61–73. doi:10.1016/j.icarus.2012.11.011

Schüller, K., and Kowalski, J. (2019). Melting probe technology for subsurface

exploration of extraterrestrial ice – critical refreezing length and the role of gravity.

Icarus 317, 1–9. doi:10.1016/j.icarus.2018.05.022

Schulze-Makuch, D., and Irwin, L. N. (2002). Energy cycling and

hypothetical organisms in Europa’s ocean. Astrobiology 2, 105–121.

doi:10.1089/153110702753621385

Schulze-Makuch, D., and Irwin, L. N. (2018). Life in the universe: expectations and

constraints. 3rd edition. Springer, 343.

Shibley, N. C., and Goodman, J. (2024). Europa’s coupled ice–ocean system:

temporal evolution of a pure ice shell. Icarus 410, 115872. doi:10.1016/j.icarus.

2023.115872

Siegert, M. J., and Kennicutt, M. C. (2018). Governance of the exploration

of subglacial Antarctica. Front. Environ. Sci. 6, 103. doi:10.3389/fenvs.

2018.00103

Smith, H. J., Dieser, M., McKnight, D. M., SanClements, M., and Foreman, C. (2018).

Relationship between dissolved organic matter quality and microbial community

composition across polar glacial environments. FEMS Microbiol. Ecol. 94, fiy090.

doi:10.1093/femsec/fiy090

Smith, I. E. M., and Price, R. C. (2006). The Tonga–Kermadec arc and

Havre–Lau back-arc system: their role in the development of tectonic and

magmatic models for the western Pacific. J. Volcanol. Geotherm. Res. 156, 315–331.

doi:10.1016/j.jvolgeores.2006.03.006

Soderlund, K. M. (2019). Ocean dynamics of outer solar system satellites. Geophys.

Res. Lett. 46, 8700–8710. doi:10.1029/2018gl081880

Soderlund, K. M., Kalousová, K., Buffo, J. J., Glein, C. R., Goodman, J. C., Mitri, G.,

et al. (2020). Ice-ocean exchange processes in the Jovian and Saturnian satellites. Space

Sci. Rev. 216, 80–57. doi:10.1007/s11214-020-00706-6

Sohl, F., Spohn, T., Breuer, D., and Nagel, K. (2002). Implications from Galileo

observations on the interior structure and chemistry of the Galilean satellites. Icarus

157, 104–119. doi:10.1006/icar.2002.6828

Sotin, C., Tobie, G., Wahr, J., et al. (2009). “Tides and tidal heating on Europa,” in

Europa Pappalardo RT, McKinnon WB. Editor K. K. Khurana (The University of Arizona

Press), 85–118.

Sparks, W. B., Schmidt, B. E., McGrath, M. A., Hand, K. P., Spencer, J. R., Cracraft,

M., et al. (2017). Active cryovolcanism on Europa? Astrophys. J. Lett. 839, L18.

doi:10.3847/2041-8213/aa67f8

Spencer, J. R., and Nimmo, F. (2013). Enceladus: an active ice world in the Saturn

system. Annu. Rev. Earth Planet. Sci. 41, 693–717. doi:10.1146/annurev-earth-050212-

124025

Srama, R., Ahrens, T. J., Altobelli, N., Auer, S., Bradley, J. G., Burton, M., et al. (2004).

TheCassinicosmicdustanalyzer.Space Sci. Rev. 114, 465–518.doi:10.1007/s11214-004-

1435-z

Storrie-Lombardi, M. C., and Sattler, B. (2009). Laser-induced fluorescence emission

(L.I.F.E.): in situ nondestructive detection of microbial life in the ice covers of antarctic

lakes. Astrobiology 9, 659–672. doi:10.1089/ast.2009.0351

Stratmann, T., Simon-Lledó, E., Morganti, T. M., de Kluijver, A., Vedenin,

A., and Purser, A. (2022). Habitat types and megabenthos composition from

three sponge-dominated high-Arctic seamounts. Sci. Rep. 12, 20610. doi:10.1038/

s41598-022-25240-z

Tacconi, L. J., Arridge, C. S., Buonanno, A., et al. (2021). Voyage 2050 final

recommendations from the voyage 2050 senior committee.

Terra-Nova, F., Amit, H., Choblet, G., Tobie, G., Bouffard, M., and Čadek, O. (2023).

The influence of heterogeneous seafloor heat flux on the cooling patterns of Ganymede’s

and Titan’s subsurface oceans. Icarus 389, 115232. doi:10.1016/j.icarus.2022.115232

Thombre, R. C., Vaishampayan, P. A., and Gomez, F. (2020). “Applications

of extremophiles in astrobiology,” in Physiological and biotechnological aspects of

extremophiles. Editors R. Salwan, and V. Sharma (Academic Press London), 89–104.

Toner, J. D., and Catling, D. C. (2020). A carbonate-rich lake solution to the

phosphate problem of the origin of life. Proc. Natl. Acad. Sci. U.S.A. 117, 883–888.

doi:10.1073/pnas.1916109117

Trumbo, S. K., and Brown, M. E. (2023). The distribution of CO2 on Europa indicates

an internal source of carbon. Science 381, 1308–1311. doi:10.1126/science.adg4155

Tufts, B. R., Greenberg, R., Hoppa, G., and Geissler, P. (1991). Astypalaea Linea: a

large-scale strike-slip fault on Europa. Icarus 141, 53–64. doi:10.1006/icar.1999.6168

Vance, S. D., Bouffard, M., Choukroun, M., and Sorin, C. (2014). Ganymede׳s

internal structure including thermodynamics of magnesium sulfate oceans in contact

with ice. Planet Space Sci. 96, 62–70. doi:10.1016/j.pss.2014.03.011

Vance, S. D., Craft, K. L., Shock, E., Schmidt, B. E., Lunine, J., Hand, K. P., et al.

(2023). Investigating europa’s habitability with the Europa clipper. Space Sci. Rev. 219,

81. doi:10.1007/s11214-023-01025-2

Villanueva, G. L., Hammel, H. B., Milam, S. M., Faggi, S., Kofman, V., Roth, L., et al.

(2023a). Endogenous CO2 ice mixture on the surface of Europa and no detection of

plume activity. Science 381, 1305–1308. doi:10.1126/science.adg4270

Villanueva, G. L., Hammel, H. B., Milam, S. M., Kofman, V., Faggi, S., Glein, C. R.,

etal.(2023b). JWSTmolecularmapping andcharacterizationofEnceladus’waterplume

feeding its torus. Nat. Astron. 7, 1056–1062. doi:10.1038/s41550-023-02009-6

Waite, J. H., Glein, C. R., Perryman, R. S., Teolis, B. D., Magee, B. A., Miller, G.,

et al. (2017). Cassini finds molecular hydrogen in the Enceladus plume: evidence for

hydrothermal processes. Science 356, 155–159. doi:10.1126/science.aai8703

Waldmann, C., and Funke, O. (2020). The TRIPLE/nanoAUV initiative a technology

development initiative to support astrobiological exploration of ocean worlds. CEAS

Space J. 12, 115–122. doi:10.1007/s12567-019-00275-7

Weber, J. M., Marlin, T. C., Prakash, M., Teece, B. L., Dzurilla, K., and Barge, L.

M. (2023). A review on hypothesized metabolic pathways on Europa and Enceladus:

space-flight detection considerations. Life 13, 1726. doi:10.3390/life13081726

Weinstock, L. S., Zierke, S., Eliseev, D., Linder, P., Vollbrecht, C., Heinen, D., et al.

(2021). The autonomous pinger unit of the acoustic navigation network in EnEx-

RANGE: an autonomous in-ice melting probe with acoustic instrumentation. Ann.

Glaciol. 62, 89–98. doi:10.1017/aog.2020.67

Weissbrodt, P., Raupach, L., and Hacker, E. J. (1994). Improved method for

contamination control during fabrication of space equipment. Proc. Space Opt. 1994

Space Instrum. Spacecr. Opt. 2210, 672–680. doi:10.1117/12.188127

Wesche, C., and Dierking, W. (2016). Estimating iceberg paths using

a wind-driven drift model. Cold Regions Sci. Technol. 125, 31–39.

doi:10.1016/j.coldregions.2016.01.008

Wierzchos, J., Casero, M. C., Artieda, O., and Ascaso, C. (2018). Endolithic microbial

habitats as refuges for life in polyextreme environment of the Atacama Desert. Curr.

Opin. Microbiol. 43, 124–131. doi:10.1016/j.mib.2018.01.003

Wolfenbarger, N. S., Fox-Powell, M. G., Buffo, J. J., Soderlund, K. M., and

Blankenship, D. D. (2022). Brine volume fraction as a habitability metric for europa’s

ice shell. Geophys. Res. Lett. 49, e2022GL100586. doi:10.1029/2022gl100586

Wong, T., Hansen, U., Wiesehöfer, T., and McKinnon, W. B. (2022). Layering by

double‐diffusive convection in the Subsurface Oceans of Europa and Enceladus. J.

Geophys. Res.:Planets 127, e2022JE007316. doi:10.1029/2022je007316

Zolotov, M. Y., and Kargel, J. S. (2009). “On the chemical composition of Europa’s icy

shell, ocean, and underlying rocks,” in Europa Pappalardo RT, McKinnon WB. Editor K.

K. Khurana (The University of Arizona Press), 431–458.

Zolotov, M. Y., and Shock, E. L. (2001). Composition and stability of salts on the

surface of Europa and their oceanic origin. J. Geophys. Res.:Planets 106, 32815–32827.

doi:10.1029/2000je001413

Frontiers in Astronomy and Space Sciences 18 frontiersin.org