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)

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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

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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

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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

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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)

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