Exploring icy satellites for their Astrobiological potential from an astronomical point of view

Athena Coustenis

LESIA, Paris-Meudon Observatory France Cassini-Huygens Quelques points de considération Aspects astrobiologiques: chimie organique, eau liquide (en surface ou à l’intérieur), sources d’énergie (activité interne), stabilité

Les satellites de glace avec organiques : Titan, Encelade, Triton. avec une activité évidente : Encelade, Triton, Io, (Titan?) avec de l’eau liquide à l’intérieur (à confirmer): Europe, Ganymède, Encelade, Titan

A l’exception de Titan, les satellites de glace avec des océans subsurfaciques possibles (Europe, Ganymède, Callisto) ou une activité cryovolcanique évidente (Encelade, Triton) résident à l’intérieur des magnétosphères des planètes géantes, mais les deux derniers ne sont pas dans la partie avec l’irradiation surfacique extrême et destructive pour les organiques.

Quel est le potentiel astrobiologique de chacun de ces satellites? Exploring the Habitability of Icy Worlds: The System Mission (JUICE)

The EJSM Science Study Team

 2009 All rights reserved. EJSM Theme: The Emergence of Habitable Worlds Around Gas Giants • Goal 1: Determine if the Jupiter system harbors habitable worlds • Goal 2: Characterize Jupiter system processes – Ocean characteristics (for Europa and Ganymede and perhaps other satellites) – Satellite system – Ice shells and subsurface water – Jupiter atmosphere – Deep internal structure, and (for – Magnetodisk/magnetosphere Ganymede) intrinsic magnetic field – Jovian system Interactions – External environments – Jovian system origin – Global surface compositions – Surface features and future landing sites

Emphasis on icy moon habitability and Jupiter system processes 5 JGO Science: Overview • Key JGO science phases – Ganymede: Detailed orbital study . Elliptical orbit first, then circular orbit – Jupiter system: In-depth exploration . From Jupiter orbit, synergistically with JEO – Callisto: In-depth study and mapping . Multiple flybys using a resonant orbit • Science Objectives: – Ganymede: Characterize Ganymede as a planetary object, including its potential habitability – Satellite System: Study the Jovian satellite system – Jupiter: Study the Jovian atmosphere – Magnetosphere: Study the Jovian magnetodisk / magnetosphere – Jupiter system: Study the interactions occurring in the Jovian system

6 Ganymede studies with JUICE Tidal deformation Geology and Topography • Presence and extent of a subsurface ocean • Ice shell and subsurface water • Deep internal structure, dynamo, magnetic field • Coupling among surface, exosphere, Deep Interior and Magnetic Field and magnetosphere • Surface composition and chemistry • Surface features, tectonic processes

• Thermal evolution, geology, and the Magnetosphere and Laplace resonance Environment

Structure and topography of Mars' Polar Cap Compositional Differences

7 1. Why is Ganymede an habitable world Theme 2: Habitability of the icy moons EJSM-Laplace Why are Ganymede and Europa habitable worlds ?

Liquid water The habitable zone is not restricted to the Earth’s orbit… Stable environment Essential elements Energy Surface habitats Deep habitats

Deep habitats Europa: Ocean • Ice • Chemistry • Geology Determine global surface compositions and chemistry, especially as related to habitability

Composition is key to understanding ocean habitability

9 Europa: Ocean • Ice • Chemistry • Geology Global surface composition & chemistry: • Organic & inorganic chemistry • Relation to geologic processes • Radiation effects • Exogenic materials

Composition is key to understanding Europa’s habitability

6/29/2011 10 Europa: Ocean • Ice • Chemistry • Geology Understand the formation of surface features, including sites of recent or current activity, and identify and characterize candidate sites for future in situ exploration

mosaic by Orion

11 Europa: “Ingredients” for Life? e-, O+, S+, … • Water:

– Warm salty H2O ocean. radiation-produced oxidants: O2, H2O2, CH2O • Essential elements:

– Accretion of CO2? – Impactors. – But radiation destroys organics in upper ~10s cm of ice. • Chemical energy:

– Radiation of H2O ⇒ oxidants. – Mantle contact: serpentinization and possible hydrothermal activity. • Relatively stable environment: hydrothermally produced reductants: H2S, H2, CH4, Fe – Large satellite retains heat. – But activity might not be steady-state. [after Stevenson, 2000] Europa: Ocean • Ice • Chemistry • Geology

Ice shell & subsurface water: • Shallow water • Ice-ocean interface • Material exchange • Heat flow variations

SHARAD, Mars north polar cap [Seu, Phillips, and the SHARAD team]

Radar sounding can characterize the ice shell

6/29/2011 8 Liquid water Theme 2: Habitability of the icy moons LIQUID WATER EJSM-Laplace Galileo evidence of liquid layers Geologic activity Induced magnetic field

Production of a ±3˚ tilt of internal dipole moment over a 10 hour period. marginally demonstrated but more data needed

Credits: Kivelson

Thermal modelling

Science questions - Existence of the liquid layer - Spatial distribution - Relationship with geology/surface

- Physical characteristics Credits: Bland Liquid water Theme 2: Habitability of the icy moons LIQUID WATER EJSM-Laplace Ganymede’s ocean: what EJSM-Laplace will do…

Induced magnetic field at multiple frequencies Magnetometer Radio and Plasma Waves Tidal deformation of the surface Radio science laser altimetry MR and HR imaging

Libration amplitudes Radio science laser altimetry

Hydrostatic equilibrium Radio science laser altimetry

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Liquid water Theme 2: Habitability of the icy moons ESSENTIAL ELEMENTS EJSM-Laplace Galileo evidences for an outstanding complexity Complex chemistry Complex dynamics Credits: Khurana

Specific albedo distribution Brines and Alteration on open field lines hydrates are good candidates

Water ice abundance – NIMS data

Science questions • What are the non–water ice chemical compounds ? • What is the endogeneous and the exogeneous repartition of this surface material ? • What is the effect of radiation weathering on these materials ? • How can we correlate the surface compounds with the sub-surface composition ? Essential elements Theme 2: Habitability of the icy moons ESSENTIAL ELEMENTS EJSM-Laplace Surface composition of the moons: what EJSM-Laplace will do… What are the surface chemical compounds ? Exogeneous versus endogeneous ? Volatiles Near-IR imaging spectrometer Ion and Neutral mass spectrometry • Major volatiles UV imaging spectrometer Particles and plasma instrument • Stable isotopes C,H,O • Noble gases Ar, Kr, Xe • Mapping of oxygen species

Ions and Neutrals • Identification • Surface 2D distribution

How does the surface relate to the subsurface ? Subsurface radar sounding Spatial coverage Sub-mm wave sounding • > 80 % at a few km/pxl • X 100 m/pxl on a few % • X10 m/pxl if needed MARSIS: South Polar Deposits Spectral coverage • > 5 times better at regional scale • Lab data quality when needed

Global scale Regional / Local scales

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Energy-Galileo Theme 2: Habitability of the icy moons ENERGY EJSM-Laplace What are the energy sources? External sources Internal sources Impactors Particles Tidal Radiogenic Secular

?

Science questions - What is the evolution of the impactor population in the Jovian system through time? - What is the amount of heat that is expelled through the surface of the moons? - How much tidal heating is distributed within the moons? Enceladus  E-ring source

Old Faithful by Starlight (Credit: Tyler Nordgren) Hidden Energy Sources ?

Radiolytic Chemistry vs Solar & Tidal Heating ?

Triton cryovolcanism (dark streaks) Energy Fluxes

mW/m2 Mimas 2.5 Enceladus 0.73 Tethys 0.48 Dione 0.44 Rhea 0.29 Callisto 0.19 Ganymede 5.4 Europa 99 Triton ~ 5

Cooper et al., PSS, 2009 Energy - external sources Theme 2: Habitability of the icy moons ENERGY EJSM-Laplace How much energy remains from the early stages ?

Impact cratering Surface heat flux Ganymede possesses the widest range in crater morphology Thermal IR mapper Low and High resolution imaging Subsurface radar sounding Vis-IR spectro imaging Sub-mm wave instrument Sub-surface radar sounding Credits: Schenk Distribution: Nearly global coverage at 200-400 m/px resolutions + HR target areas (5-50 m/px)

Present activity: monitoring on a timescale x 100 days up to years to identify potentially newly formed craters

Buto Facula

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Energy - internal sources Theme 2: Habitability of the icy moons ENERGY EJSM-Laplace How much heat is available in the interior of the moons ?

Intrinsic magnetic field Magnetometer Radio and Plasma Waves Constraints on the core size and dynamics

Gravitational field Radio science Laser altimetry Equilibrium state Averaged density profiles Mass anomalies determination

Tidal deformation Radio science Laser altimetry MR and HR imaging Equilibrium state

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Stability - Galileo Theme 2: Habitability of the icy moons STABILITY EJSM-Laplace How stable are the present states? Geology as a witness of moon’s evolution Stability of the system

Science questions -What do geologic features tell us about the past and present internal activity ? -How did the habitable zone evolve through time ? Stability - resonnance Theme 2: Habitability of the icy moons STABILITY EJSM-Laplace Stability of the environments: orbital changes and tidal heating

Orbital changes of the satellites Tidal deformation Wide angle camera Laser altimetry Narrow angle camera Radio science Radio tracking

Global scale Regional / Local scales

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Stability - resonnance Theme 2: Habitability of the icy moons STABILITY EJSM-Laplace Stability of the environments: geology as a witness of moon’s activity

Imaging from medium to high resolution Wide angle camera Narrow angle camera

Imaging spectroscopy Vis-IR Imaging x 50 spectrometer

Topography / Morphology Laser altimetry

Subsurface exploration Radar sounding

Jupiter System ~2.5 y Elliptical Circular 500 Circular 200 15 moon flybys 40 days 80 days 60 days Single fly-by option of Europa – top-priority sites for astrobiology and geology

CRITERIA - Evidence for material mobility from the interior of the satellite. It can support the connection between the internal liquid water layers (the potential habitable environment) and the surface. - Concentration of non-ice components. These A3: Chaos material with matrix showing materials can provide block elements or/and pre‐existing structure, associated with dark plains, energy for the microorganisms. If they are salts, possibly from emplacement of liquid material (e.g., they can be an evidence of internal aqueous Fagents, JGR 108, 5139-5158, 2003). reservoirs. - Relative youth, which increases the chances for finding or preserving biosignatures due to less time of exposure to the radiation environment. - Textural roughness, because it can be useful for shielding. This is not a good parameter if the area is considered as a future landing site - Stable or gradually changing environment, for preserving the signatures coming from the A1: Class of chaos material with matrix and rafts of interior. pre‐existing ridged plains moved with respect to one -Searching for organics or the mechanisms of another (e.g., Spaun et al., GRL 25, 4277-4280, 1998); their destruction (see following comment) and far-reaching bright rays of crater Pwyll; right-angle furthermore for any signs of volcanism on Europa intersection of complex ridges Asterius & Agave Linea (also see attached comment) north of . GEOLOGY ASTROBIOLOGY Prioritization map Prioritization map Low Medium High Highest Low Moderate High Highest Single fly-by option – trailing quadrant

Map from: R. Jaumann’s email to SST, 26-05-2011 Conclusions • Liquid water, energy sources, elements and stability are needed for life as we know it, and may all be present on Ganymede and Europa • We need more extensive investigations at this stage to determine with precision all of these factors on Ganymede • Astrobiological challenge for Europa is to determine limits on organics and any cryovolcanic activity in a hostile surface irradiation and oxidation environment • The presence and characteristics of an interior liquid water ocean on Ganymede should be determined by JUICE and possibly some information can be gained also on Europa’s ocean through 1-2 well-targeted flybys. Le processus de sélection de la missions L1 (2)

Janvier 2011: Publication ESA des « Yellow book » Février 2011: Présentation publique des missions L Scénario jusqu’à récemment: Sélection de (au plus) 2 missions L au SPC de février 2012.

Message de l’ESA du 14 mars : Compte tenu de l’incapacité des partenaires à s’engager sur aucun des trois missions: - Nécessité de reporter toute décision jusqu’en 02/2012 - action auprès des consortiums pour étudier ces missions maintenant essentiellement européennes (6 mois environ) - les nouvelles missions proposées repasseront devant les Processus d’évaluation instances d’évaluation début 2012 évaluation Première analyse: - Besoin de conduire de nouvelles assessment phases

- Un retard de L1 est à redouter 30 2011 2012 Statut actuel des missions L -Les Phase 0 pour toutes les missions L (à l’exception de LISA qui a été reconduite depuis Horizon 2000 Plus) ont été commencées à la mi-2008. - Début Février 2009 l’ESA et la NASA ont annoncé ensemble la décision de donner la priorité au lancement de la mission EJSM-Laplace parmi les candidates Outer Planets. A ce moment les études officielles ESA sur TandEM/TSSM ont été terminées. Des études sur le ballon pour Titan ont été poursuivies au CNES et au JPL. - Après un appel en 2009, des études industrielles sur EJSM-Laplace et IXO ont été conduites et terminées ainsi que le « Yellow Book » pour ces concepts vers la fin 2010. Tous les candidats (EJSM-Laplace, IXO et LISA) ont été étudiés en collaboration avec la NASA (et dans le cas de IXO, aussi avec JAXA). - Les résultats des ces phases d’assessment et les objectifs scientifiques des missions furent présentées à la communauté Scientifique Européenne le 3 Février 2011. - Depuis, et en conséquence de l’évolution de la situation programmatique de la NASA concernant les missions L (aucune des 3 missions L ne fut classée en tant que priorité no 1 des Decadal Surveys), la NASA et la JAXA ont confirmé qu’il était très improbable de pouvoir fournir la participation importante prévue pour aucune des 3 missions candidates selon la planification de l’ESA (càd pourFolie 31 Cosmic Vision 2015 - 2025 un lancement tôt 2020). Statut actuel des missions L (suite) - Par conséquent, l’Executif de l’ESA a terminé les Assessment Phase pour les 3 candidates L1 au lancement en 2020 et commença une reformulation rapide visant à définir les candidates viables pour un lancement en 2022 en tant que large mission menée par l’Europe (ou seulement Européenne) pour déterminer si les objectifs scientifiques des missions candidates L (ou lesquels parmi ces objectifs) pourraient être atteints suite à ces changements. Il s’en suit que cela permettrait de savoir lesquelles de ces missions pourraient être implementées dans le contexte d’une mission ESA. - Les thèmes scientifiques principaux que les 3 missions originales couvraient étaient: • Le système de Jupiter avec l’accent sur Ganymède et les satellites de glace pour EJSM-Laplace (désormais JUICE); • Des observations aux rayons X des sources cosmiques pour IXO (désormais ATHENA), avec une grande surface collective et haute résolution spectrale; • la détection et étude poussée des sources des ondes gravitationnelles cosmiques pour LISA. - Les activités en cours visent à établir si une ou plusieurs parmi les missions candidates dans les 3 thèmes scientifiques ci-dessus peuvent être implémentées en tant que European-only (or European-led) pour un lancement vers 2022. Cette activité est menée tambour battant par l’Executif de l’ESA et les nouveaux Science Study

Teams des spécialistes des missions. Folie 32 Cosmic Vision 2015 - 2025 - Pour préserver la possibilité d’un lancement vers 2022 il faut qu’une décision sur la