Planetary Geology in the outer solar system: the search for materials and the research of astrobiology Anezina Solomonidou Caltech – NASA/JPL Giant Planet Systems 1. Why is Ganymede an habitable world Habitability in our Solar System: Extension of the zone

*Water Surface habitats Deep habitats *Stable environment *Organics *Energy

Deep habitats

The habitable zone is not restricted to the Earth’s orbit… ESA’s Cosmic Vision 2015-2025: Ocean Worlds Planets and Life

The NASA ‘Explore in situ the surface and Roadmap to subsurface of solid bodies in the Ocean Worlds Solar System most likely to host or have hosted life’ NASA (OPAG/ROW): ‘identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find.’

Dragonfly - NASA

…vast oceans beneath thick ice crusts 4 Hendrix et al. 2019 Why does this matter? Geology - Habitability Understand the geology Unveil the connection between interior-surface-atmosphere

Full interpretation Full interpretation of of composition composition Detection of cryovolcanism and internal activity

ESA/ATG Medialab

5 Coustenis, Raulin, Bampasidis, Solomonidou (2012). Springer Solomonidou et al. (2011). J of Cos., Vol. 13, pp. 4191-4211 A. Karagiotas/NAI/JPL Icy moons: The mission Titan Dragonfly: a rotocraft mission to Titan Mission type: Astrobiology Launch: 2027 Landing: 2036

7 CASSINI (2004-2017) (2005)

A SPACECRAFT WITH 'HUMAN ABILITIES’

12 instruments on Cassini

6 instruments on Huygens Huygens (01/2005): The descend and landing of Huygens

110-0 km 3d Parachute (2h13min) 156 km 1st Parachute (2 sec) 155-110 km 2nd Parachute (15 min)

PHOEBE

IAPETUS

HYPERION Atlas Daphnis

Pan Pandora

Buratti et al., Science 2019 CASSINI (2004 - 2017): Highlights

Titan and the Cassini mission

Atmosphere:

• N2 (Voyager, 1980) (98.4%)+CH4 (Kuiper, 1944) (1.5%)+H2 • Hydrocarbons, nitriles and oxygen compounds (traces) • Intense ionospheric chemistry in the upper levels (INMS)

Surface: • Complex surface with multivariable geological expressions • Surface – atmosphere interaction • Active methane cycle

Cassini 1979 1980 1981 2004-2017

Huygens 2005

15 Surface units

Mountains Dunes

Volcanoes?

Drainage networks Lakes

Jaumann et al. 2009; Lopes & Solomonidou, 2014 Lacustrine

Lakes and Seas The mystery of Titan The methane cycle and the interior

CH photolysis = Ethane + organics Process: Irreversible 4 like Earth’s hydrological cycle Various complex hydrocarbons, which form Titan’s haze layer Methane on Titan plays the role of water on Earth

Mystery of the surface: what is the composition? Methane replenishment: where is the reservoir?

Liquid hydrocarbon reservoir? Cryovolcanism?

Tobie et al. 2005 18 Raulin, 2008 Titan: Surface – Subsurface – Habitability Habitability of Hydrocarbon Worlds: Titan and Beyond

The single compelling question for this research is: What habitable environments exist on Titan and what resulting potential biosignatures should we look for?

How are molecules transported across the surface and deposited/modified?

How would we detect biosignatures that reach the surface and atmosphere? Titan’s surface from 3 Cassini instruments ✓Surface can only be imaged with IR and radar ✓We used a multi-swath mosaic from Cassini’s RADAR as a basemap ✓Synthetic Aperture Radar (SAR) gives best resolution of 300 meters per pixel ✓SAR swaths provide 65% coverage of the moon

RADAR: RADAR: Radiometry SAR mode mode

ISS SARTopo

VIMS

20 Geomorphological types SAR Malaska et al., Lopes et al. 2016, Solomonidou et al. 2018 Undifferentiated Plains Streak-like Plains Variable Plains Scalloped Plains

Hummocky Labyrinth Dunes Alluvial fans Maculae

Radebaugh et al. 2016 Impact craters EvaporitesEvaporites Cryovolcanics

Solomonidou et al. 2016 21 Barnes et al. 2013 Lopes et al. 2013 The 1st global geomorphological map of Titan

2400 km

Titan is dominated by plain (65%) and dune fields (17%)

(Lopes et al., 2020, Nature Geosciences) The mystery of Titan Map to it! (or finalizing the Titan Global map)

23 The VIMS data

How to extract meaningful surface info from VIMS ‘Methane windows’ centered at 0.93, 1.08, 1.27, Titan spectrum 1.59, 2.03, 2.69-2.79 and 5.00 μm from VIMS However The haze extinction in the near-IR decreases with w/v, and methane absorption is not marginal Extracting information on the lower atmosphere and the surface from near-IR spectra requires a good understanding of the methane and haze contributions to the opacity. Our approach 1. Study Titan’s surface with specific tools 2. Use of theoretical and experimental data in a modular Radiative Transfer model

Results Haze effect + Surface albedo

24 Surface albedo retrieval from VIMS A Radiative transfer code (RT) for Titan Code Plane-parallel (1D) Temperature profile HASI (Fulchignoni et al. 2005) CH4 mixing ratio GCMS (Neimann et al. 2010) Haze parameters DISR (Tomasko et al. 2008, de Bergh et al. 2011)

12 13 12 Atmospheric gases CH4, CH4, CH3D, CO, and collisions N2-N2 & N2-H2 (de Kok et al. 2007; Lafferty et al. 1996, McKellar et al. 1989) CH4 NEW UPDATED absorption (Boudon et al., 2006; Campargue et al. 2012, 2015 & Rey et al., 2017, HITRAN, coefficients GEISA, etc) Surface component candidates ices and tholins (Bernard et al. 2006; Coll et al. 2006; Brassie et al. 2015; B. Schmitt & S. Philippe private communications)

✓Test simulations with various haze opacities

✓Correlation between simulations and data

✓Best fit between VIMS and simulation Solomonidou et al. 2014, JGR

25 Hirtzig et al. 2013, Icarus; Solomonidou et al. 2014, JGR; Solomonidou et al. 2016, 2018 ,2019 Icarus 2020 A&A; Lopes et al. 2016, Icarus; Bonnefoy et al. 2016, Icarus Candidate materials for the surface of Titan New library of ices Work from B. Schmitt, S. Philippe & P. Coll GhoSST database

H2O with a series of 15 grains sizes: 10, 20, 30, 40, 50, 75, 100, 150, 200, 250, 300, 400, 500, 750, and 1000 µm.

We try to fit the albedos with the most adequate selection among 4 constituents x various grain sizes=

When the best fit is obtained we identify the major constituent

The solution is not unique but we can retrieve the most probable major constituents current work includes CH4, C2H2, C2H4, C2H6, C2H8, CO2, NH3, H2O, HC3N 26 4 projects on Titan’s key areas Solomonidou et al. (2014, 2016, 2018, 2020)

9 distinct geomorphological units +HLS

Significant differences in albedo among various areas / 3 distinct albedo groups Project 2: Retrieval of pure surface albedo: Surface processing and weathering

The fact that the spectral behavior is different for each of these areas, is indicative of diverse chemical compositions and origins.

The wind transfers dune material to equatorial plains Lopes et al. Icarus, 2016 Solomonidou et al. JGR, 2018

75-120% haze contribution Solomonidou et al. JGR, 2018 wrt DISR Funded by NASA CDAP Project 2: Major constituent on various geomorphological types

✓ Very good correlation in the classification between SAR and VIMS ✓ 3 main types of surface albedo – 3 main types of major constituents: water ice: at latitudes higher than 30ºN and 30ºS tholin-like material, and an unknown very dark material: at equator ✓ Titan’s surface composition has a significant latitudinal dependence Project 3: Retrieval of pure surface albedo = Surface processing and interior

The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan’s surface and, by implication, its interior.

Global amplitude pattern of maximum diurnal tidal stresses, Strongest cryovolcanic 휎tidē , overlaid onto an ISS map of candidate (Lopes et al. 2013) Possible cryovolcanic candidate Titan’s surface (Sohl et al. 2014). (Solomonidou et al. 2014)

Reported temporal spectral changes (Nelson et al. 2009) Solomonidou et al. JGR, 2016 Funded by CDAP Surface changes on Titan Tui Regio through time 2005-2009 / 2005-2006 Haze evolution Haze evolution Haze evolution Haze evolution

50% 50%

factor of 2 factor of 2

20-50% decrease in surface albedo Increase in albedo up to a factor of 2 at all wavelengths at all wavelengths Tui Regio is getting darker Sotra Patera is getting brighter Solomonidou et al. 2016, Icarus Project 3: Spectral & emissivity of raised lake ramparts Solomonidou et al. 2019, Icarus

Funded by CDAP & NAI

Lakes with ramparts seem to be the youngest feature on Titan Project 4: The chemical composition of impact craters (Solomonidou et al. 2020, A&A)

Titan, like Earth, has the limited number Why are they important? of impact craters Rare opportunity to understand the unlike the heavily cratered surfaces of the subsurface composition of Titan other Saturnian satellites

Dragonfly’s landing site: the crater So… what we know so far

• Dunes are the youngest feature on Titan, along with lakes • Plains are the next youngest, act as a fill unit • Mountains are likely the oldest unit

• Mapping results (1 meter of crust) suggest the equatorial and mid-latitudes of Titan are dominated by organic materials being deposited and emplaced by aeolian activity VIMS results (few μm of the surface) show a latitudinal dependence of Titan’s surface composition, with water ice at latitudes beyond 30°N -30°S, while Titan’s 2.23 % 14.98 % equatorial region appears to be dominated by organics. 0.71 % 2.11 % The poles are dominated by fluvial and 18.60 % 61.37 % lacustrine processes (Lopes et al., 2020, Nature Geosciences) Ongoing work Organics & Water-ice

dark + tholinwater-like- ice water-ice + tholin- Tholin-like + like water-ice dark + waterorganics-ice water-ice + dark Tholin-like + dark

35 Basemap: ISS (NASA/JPL-Caltech/SSI-PIA14908) ‘’Acetylene! Acetylene!’’ Biosignature detection Interior – Surface - Atmosphere Determine the pathways for organic materials to be transported (and modified) from the atmosphere to surface and eventually to the subsurface ocean (the most likely habitable environment).

Radiative Transfer

Global geological map: Morphology + Chemistry For Surface/Subsurface

The connection to the dynamic interior: search for biosignatures

Identification of surface constituents leads to distinction between endogenic and exogenic processes = Surface – Interior connection (ocean) Ganymede Europa Callisto Future missions NASA/JPL

Europa Clipper Mission launch: TBD/2024 target: Europa status: Selected Future missions ESA

JUICE – Jupiter System

Launch: 2023 Jupiter: 2030-31

Water Type: Orbiter/Lander Status: In preparation Habita Launch Date: 2023 bility Target: Jupiter, Europa, Chemistry Energy Ganymede, Callisto Ongoing work The JUICE mission

Cassini lesson learnt: Cassini RADAR Vs JUICE RIME Callisto & Ganymede’s regions of interest Ganymede book: Ganymede’s Hydrosphere Properties of ices of Jovian surfaces

Lesson learnt from Cassini

Ganymede – class IV • Largest satellite in the solar system • A deep ocean • Internal dynamo and an induced Europa – class III magnetic field – unique Callisto – class IV • A deep ocean • Richest crater morphologies • Best place to study the impactor history • An active world? • Differentiation – still an enigma • Best example of liquid • Best example of liquid environment • Only known example of non active but environment in contact with41 trapped between icy layers ocean-bearing world silicates Experiments on Jovian ices Applicability to JUICE and its targets Project funded by the 2018 Research opportunity of the ESAC faculty to A. Solomonidou

-Thermal & Electrical conductivity chambers at CAB Ultra-high vacuum ISAC High Pressure HPPEC works at high works at high vacuum, surface pressure, interior conditions conditions

-Fabrication of ices a climatic chamber at ITEFI-CSIC

Pure ice + salts, CO2, SO2, NH3 H2O-MgSO4, H2O-NaCl, H2O-NH3 ‘Measurements of thermal and dielectric properties of ices in support to future ‘Black racing car’: radar measurements of Jovian Icy moons’ GeoRadar that sends and collects the radar 42signal traveling through the ice. Regions of Interest on Ganymede’s and Callisto’s surface as potential targets for ESA’s JUICE mission support the planning activities of the JUICE team

major aspects based on the science objectives of the JUICE mission

7 categories of surface features and terrain types

crucial to understand the geological evolution of Ganymede and Callisto reaching from past and/or present K. Stephan These RoIs will help us cryovolcanic activity to space weathering T. Roatsch fully exploit the potential processes F. Tosi of JUICE by O. Witasse highlighting the A. Solomonidou requirements for each H. Hussmann instrument, P. Palumbo optimizing their synergy F. Poulet and coordination in the N. Altobelli observation planning. JUICE WG2 team 43 Database for current and future mission preparation JUICE – Europa Clipper Lab Experiments for the surface/subsurface/ocean Scope: provide a library of data that would help on the preparation of the future missions, their potential synergy and the expected measurements and science return Drill sites: locations on Earth with different surface spectral characteristics for subsurface exploration (Malaska et al. 2020) Scope: relate surface characteristics (spectra) of icy worlds to subsurface habitability = Candidate landing and drilling sites

Exobiology Extant Life Surveyor Europa (EELS) Lander The future Mission concepts / White papers

Shaping ESA’s space science plan for 2035-2050

Titan - Enceladus

We advocate the L-class or M-class acknowledgement of Titan and (Titan and Enceladus Enceladus science as highly relevant to ESA’s long-term Orbiter; Bioinspiration roadmap (Sulaiman et al. White Paper; and Biomimetrics) Experimental Astronomy, submitted) S-class or F-class (Plume flyby)

POSEIDON Titan POlar Scout/orbiteEr and In situ lake lander and DrONe explorer (POSEIDON) (Rodriguez et al. White Paper, Experimental Astronomy, submitted)

Future exploration of Titan’s “aqueous Titan biotope” ✓ Orbiter ✓ Lake lander ✓ Amphibious drone ✓ Mini-drones The future Mission concepts / White papers

Planetary Science and Astrobiology Decadal Survey 2023-2032 Titan Even after Huygens and Dragonfly, we will only have in situ data for low latitudes, whose The Science Case for a Titan nature strongly differs from the polar regions. Flagship-class Orbiter with Probes (Nixon et al. White Paper) A new dedicated Titan mission that addresses both global and local (polar) science and provides long-term temporal coverage of the atmosphere is required.

New Frontiers Titan Orbiter (Barnes et al. White Paper) We recommend a New-Frontiers-class Titan orbiter to complement Dragonfly with global geology, geophysics, and atmospheric science.

Titan: Earth-like on the Outside, Ocean World on the Inside (MacKenzie et al. White Paper) Mission opportunities in addition to Dragonfly in the next decade. The future Mission concepts / White papers Ice Giant Systems: The scientific ESA Voyage 2050 potential of orbital missions to Decadal Survey 2023-2032 Uranus and Neptune (Fletcher et Mars – Ice Giants al. ESA White Paper, PSS 191)

The Quest for Life Leads Underground: Exploring Modern- Day Subsurface Habitability & Extant Life on Mars (Stamenković et al. ESA White Paper) Exploring Uranus’ natural satellites and Neptune’s captured moon Triton could reveal how Ocean Worlds form and remain active, redefining the extent of the habitable zone in our Solar System

New Frontiers-class Uranus Orbiter: Exploring the feasibility of achieving multidisciplinary science with a mid-scale mission (Cohen et al. Decadal) Exploration of both Ice Giants will require lower-cost missions, such as a New Frontiers (NF)-class orbiter to Uranus. Thank you all for your attention!

Anezina.Solomonidou @jpl.nasa.gov