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 Titan Icy moons: The Dragonfly mission Titan Dragonfly: a rotocraft mission to Titan Mission type: Astrobiology Launch: 2027 Landing: 2036 7 CASSINI (2004-2017) HUYGENS (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 / Sotra Patera 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 Selk 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 +