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Candidate Regions on Titan As Promising Landing Sites for Future in Situ Missions

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Candidate Regions on Titan As Promising Landing Sites for Future in Situ Missions CANDIDATE REGIONS ON TITAN AS PROMISING LANDING SITES FOR FUTURE IN SITU MISSIONS Solomonidou Anezina (1,2), Coustenis Athena(1), Jaumann Ralf(3), Stephan Katrin(3), Sohl Frank(3), Hussmann Hauke(3), Hirtzig Mathieu(4,1), Bampasidis Georgios(1,5), Bratsolis Emmanuel(5), Moussas Xenophon(5), Kyriakopoulos Konstantinos(2). (1) LESIA - Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot –Meudon, France, ([email protected]) (2) National and Kapodistrian University of Athens, Department of Geology and Geoenvironment, Athens, Greece, ([email protected]) (3) DLR, Institute of Planetary Research, Berlin, Germany, ([email protected]) (4) Fondation La Main à la Pâte, Montrouge, France, ([email protected]) (5) National and Kapodistrian University of Athens, Department of Physics, Athens, Greece, ([email protected]) ABSTRACT surface. Many of them have counterparts in Earth The highly successful and still on-going Cassini- geology, but the materials in play are different. The Huygens mission to the Saturnian system points to the diversity of surface formational mechanisms include need for a return mission, with both remote and in situ potential cryovolcanism on a number of areas such as instrumentation. The surface of Saturn’s moon Titan, Tui Regio (20°S, 130°W), Hotei Regio (26°S, 78°W) hosts a complex environment in which many processes and Sotra Patera (15°S, 42°W) [4]. In this work, we occur shaping its landscape. Several of its geological actually focus on these areas from VIMS and RADAR features resemble terrestrial ones, albeit constructed data. The two cameras of Cassini/VIMS have observed from different material and reflecting the interior- the surface of the candidate areas at visible and infrared surface-atmosphere exchanges. The resulting observed wavelengths, giving insights about their composition. morphotectonic features and cryovolcanic candidate Furthermore, the Cassini/RADAR with SAR acquires regions could benefit from further extensive topographic pictures using microwaves, penetrating exploration by a return mission that would focus on Titan's hazy thick atmosphere. Combined these aspects with adapted state-of-the-art investigations specifically of Hotei Regio and Sotra instrumentation affording higher spectral and spatial Patera suggest that both instruments are in agreement resolution and in situ capabilities. We suggest that with results pointing to a variety of geological some features on Titan are more promising candidate processes having occurred in the past [4, 5] or recently locations for future landing and we present the case for [6], possibly indicating cryovolcanism. Indeed, data Tui Regio, Hotei Regio and Sotra Patera as to why they correlation and analysis from VIMS and RADAR could provide a wealth of new scientific results. provided us with images and mosaics combining both spectral and morphological information [4]. However, 1. INTRODUCTION the problem of atmospheric haze scattering and particle Data retrieved from the Visual and Infrared absorption is still present, making surficial imaging Mapping Spectrometer (VIMS) [1], the Synthetic ambiguous unless a complete and accurate modelling Aperture Radar (SAR) and RADAR [2] and the of the atmospheric contribution is performed. In our Imaging Science Subsystem (ISS) [3] aboard Cassini processing VIMS and RADAR data, we take into and the instruments on board the Huygens probe account the atmospheric effect and photometric supplied information regarding Titan’s atmosphere, corrections, as well as filtering with a view to produce surface composition and morphology. This detailed constraints on the surficial chemical composition and approach on Titan's geological environment has morphology. The evidence of such interesting areas classified it as extremely interesting due to its complex like Tui Regio, Hotei Regio and Sotra Patera as it will surface composition. A combination with unique be shown hereafter, enhances the significance of a geological features [4, 12, 20] make Titan a prime future mission to Titan with in situ capabilities [7,8]. candidate for geological, internal and surface in situ investigation. Multiple flybys (91 to this date) of the 2. GEOLOGY OF AREAS OF INTEREST NASA/ESA Cassini-Huygens spacecraft, which is still In general, Titan’s surface appears to host diverse in commission, brought into light surficial expressions types of both smooth and rough areas of various relief that were not expected to be observed on an icy types, which - among other - include volcanic-like features and impact craters that are intermittently filled Tui Regio could represent past cryovolcanic activity by atmospheric precipitations which have been based on its morphology, relative age and chemical reported [9, 10]. In addition, Titan exhibits topographic composition. features such as mountains, ridges, faults, and aeolian and fluvial features such as dunes and lakes. b) Hotei Regio Chronologically, the surficial geological features are young and unique for a celestial satellite [11]. Hotei Regio is a 700 km-wide area that is probably volcanic in origin [4, 5] (Fig. 1). The Cassini The geological terrains of Tui Regio, Hotei SAR images confirm the interpretation that the area is a Regio, and Sotra Patera are the main focus of this study low basin surrounded by higher terrains with possible and they are proposed as interesting candidates for calderas, fault features and extensive cryovolcanic future landing sites. The wealth of data acquired from flows. Reference [5] have studied the area and VIMS and RADAR on board Cassini spacecraft and indicated significant geological features that resemble their analysis with specific software provide the terrestrial volcanic features. These are viscous flow- evidence as to why [4, 5, 21, 24]. These candidate like figures, a 1 km mountainous terrain (ridge-like) regions consist of diverse geomorphology, possible that surrounds the basin as well as dendritic channels, surface albedo changes with time and a correlation caldera-like features, dark blue patches (in RGB with the interior’s high zones of tidal potential. Not coloring) and possibly alluvial deposits. Processing of only have the data revealed the uniqueness of all three RADAR images showed that Hotei Regio is a low areas by means of morphological aspects such as basin depression, (as expected to be observed in a caldera-like features, a deep crater, high mountains and volcanic terrain) one km deep. It is filled with lobate flows, but also depicted the variability in terrestrial volcanic-like flows that are 100 to 200 km composite component. Moreover, Tui, Hotei and Sotra thick. The peripheral area lying at higher altitudes has are the only ones among the cryovolcanic candidate rough as well as smooth texture. This means the regions as in [4] that appear anomalously bright at 5µm surrounded formations are probably alluvial deposits and have been observed adequately by VIMS for a [5]. The ring-fault-like structures seen within the basin temporal variation study. The candidate regions for in present possibly a caldera-like feature. Hotei Regio is situ investigations should combine atmospheric, the first Titan area that has been reported to exhibit surficial, near sub-surficial and deep internal changes in brightness with time from July 2004 until investigations [12]. If the cryovolcanic origin of Tui, March 2006 [6]. Reference [6] described evidence for Hotei and Sotra is identified, they will stand as case photometric variability on Hotei Regio by analyzing study areas for all the aforementioned investigations. VIMS data, which could be linked to cryovolcanism and ammonia deposits. a) Tui Regio Alternatively, Tui and Hotei Regio have been Tui Regio (20°S-130°W) is one of the areas suggested to be sites of large low latitude paleolakes which was observed as anomalously bright at 5µm based on estimations of Titan’s topography [17]. In wavelength and therefore constitutes a component of addition, reference [19] suggested the presence of dry the most reliable evidence yet obtained concerning the lakebeds at Titan’s north pole with spectral activity of cryovolcanism on Titan’s surface (Fig. 1). characteristics similar to Tui and Hotei Regio, Tui Regio consists of a flow-like figure 150 km-wide suggesting a common evaporitic origin. Recent studies and extends for 1,500 km in an East-West direction [18] also suggested that the areas are the result of [13]. Theories suggest that it may be geologically exogenic deposits, either fluvial or lacustrine. young and that the resembling lava flows could be deposits of cryovolcanic activity. The analysis of c) Sotra Patera (formerly known as Sotra Facula) Cassini ISS and mainly VIMS data suggest that the area is a massive flow field since at least three long Sotra Patera, a 235 km in diameter area, has lobate spectrally distinct tendrils [13] have been recently been identified as an additional potential observed and have possibly being effused from a main cryovolcanic feature [4] and is currently under point like a caldera-like structure, fracture or fissure. investigation by means of endogenic processes that The observed geological surficial expressions such as might have shaped it (Fig. 1). Reference [4] have found calderas, ejecta deposits, alluvial terrains, flows, the that there are two peaks more than 1-km high and one low basin and more, depict the imprints of dynamic deep volcanic crater (1-km deep) and finger-like lobate activities. The area has been characterized by [14] as a flows. spectrally distinct unit in composition, especially because of its anomalous brightness at 5 µm, which has been confirmed by using updated VIMS maps from [15]. Reference [16] proposed that Tui Regio could be an active centre of cryovolcanism. Reference [13] suggested that a flow-like feature in the western part of darkest (green) RoIs. Fig. 2. PCA on VIMS data (the red spot marks the brightest RoI and the green the darkest) using specific Fig. 1. Map of Titan’s indicating three promising Principal Components (PCs) for each data cube [21]. landing sites: Tui Regio (A), Hotei Regio (B), Sotra Patera (C) [21].
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