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... These discoveries shifted the possibility of caves on other planetary bodies from hypothetical to tangible. The accelerated search for additional cave features on the Moon and Mars (refer to Cushing, 2017;Wagner & Robinson, 2021) ultimately expanded into the identification of nearly 3,000 potential subsurface access points (SAPs; this term is applied in lieu of "cave entrance" as we lack any additional evidence to suggest a cave exists) on eight planetary bodies (Titus, Wynne, Malaska, et al., 2021;Wynne, Titus, et al., 2022) and cave-bearing landscapes across the solar system. The prospect of extraterrestrial caves has steadily fueled research efforts to: ...
... • examine microbial life of tellurian caves as Mars analogs (e.g., Boston, 2004;Boston et al., 2006;Léveillé & Datta, 2010;Röling et al., 2015;Selensky et al., 2021;Westall et al., 2015); • model environments of terrestrial and potential martian cave systems (e.g., Schörghofer et al., 2018;Titus et al., 2010;Williams & McKay, 2015;Williams et al., 2010); • improve cave detection capabilities (e.g., Cushing et al., 2015;Hong et al., 2015;Pisani & De Waele, 2021;Wynne et al., 2008Wynne et al., , 2021); • develop and expand upon life detection instrumentation and techniques (e.g., Patrick et al., 2012;Preston et al., 2014;Storrie-Lombardi et al., 2011;Uckert et al., 2020); • expand the number of cave explorer robotic platforms under development (Green & Oh, 2005;Kesner et al., 2007;Morad et al., 2019;Nesnas et al., 2012;Parness et al., 2017;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021); • advance robotic sensing and navigational capabilities (e.g., Agha-Mohammadi et al., 2021;Kalita et al., 2017;Kim et al., 2021;Thakker et al., 2021); and, • propose mission concepts (e.g., Kerber et al., 2019;Phillips-Lander et al., 2020;Whittaker et al., 2021;Ximenes et al., 2012) and strategies to optimize future planetary cave exploration efforts (e.g., Rummel et al., 2014;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021;Wynne et al., 2014;Wynne, Titus, et al., 2022). values. ...
... • examine microbial life of tellurian caves as Mars analogs (e.g., Boston, 2004;Boston et al., 2006;Léveillé & Datta, 2010;Röling et al., 2015;Selensky et al., 2021;Westall et al., 2015); • model environments of terrestrial and potential martian cave systems (e.g., Schörghofer et al., 2018;Titus et al., 2010;Williams & McKay, 2015;Williams et al., 2010); • improve cave detection capabilities (e.g., Cushing et al., 2015;Hong et al., 2015;Pisani & De Waele, 2021;Wynne et al., 2008Wynne et al., , 2021); • develop and expand upon life detection instrumentation and techniques (e.g., Patrick et al., 2012;Preston et al., 2014;Storrie-Lombardi et al., 2011;Uckert et al., 2020); • expand the number of cave explorer robotic platforms under development (Green & Oh, 2005;Kesner et al., 2007;Morad et al., 2019;Nesnas et al., 2012;Parness et al., 2017;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021); • advance robotic sensing and navigational capabilities (e.g., Agha-Mohammadi et al., 2021;Kalita et al., 2017;Kim et al., 2021;Thakker et al., 2021); and, • propose mission concepts (e.g., Kerber et al., 2019;Phillips-Lander et al., 2020;Whittaker et al., 2021;Ximenes et al., 2012) and strategies to optimize future planetary cave exploration efforts (e.g., Rummel et al., 2014;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021;Wynne et al., 2014;Wynne, Titus, et al., 2022). values. ...
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We provide the first solar system wide compendium of speleogenic processes and products. An examination of 15 solar system bodies revealed that six cave‐forming processes occur beyond Earth including volcanic (cryo and magmatic), fracturing (tectonic and impact melt), dissolution, sublimation, suffusion, and landslides. Although no caves (i.e., confirmed entrances with associated linear passages) have been confirmed, 3,545 SAPs (subsurface access points) have been identified on 11 planetary bodies and the potential for speleogenic processes (and thus SAPs) was observed on an additional four planetary bodies. The bulk of our knowledge on extraterrestrial SAPs is based on global databases for the Moon and Mars, which are bodies for which high‐resolution imagery and other data are available. To further characterize most of the features beyond the Moon and Mars, acquisition (preferably global coverage) and subsequent analysis of high‐resolution imagery will be required. The next few decades hold considerable promise for further identifying and characterizing caves across the solar system.
... Presently, Earth is the only planetary body where we can monitor the full range of processes that characterize the cave environment. The terrestrial subsurface encompasses a range of cave types, which are defined by formation processes and resulting structure (Boston, 2004;Titus et al., 2021;Titus, Phillips-Lander, et al., 2020;Wynne et al., 2022). Surface conditions also vary widely as caves are distributed globally, occurring in nearly every biome on land and underwater. ...
... What sensors would provide the greatest impact to science inquiry, while not limiting the payload for mobility? ( Robots are likely to be the first explorers of planetary caves (Huber et al., 2014;Husain et al., 2013;Titus et al., 2021;Titus, Phillips-Lander, et al., 2020;. To effectively explore these targets, future robotic systems will require the functionality to: (a) properly sense their environment; (b) support and deliver scientific payloads to sites of interest; (c) plan actions and movements; and (d) negotiate a complex landscape to execute these actions. ...
... Despite our rather thorough inventories of SAPs on the Moon and Mars (Titus, Wynne, Malaska, et al., 2021;Wynne et al., 2022), our knowledge of these features is founded primarily upon the remotely sensed examination on surface expressions-save for limited gravimetric analysis of lunar SAPs (refer to Chappaz et al., 2017). The next step will be to characterize and prioritize these features for both additional imagery acquisition (e.g., Kearney et al., 2021;Wagner & Robinson, 2021) and develop and/or expound upon gravimetric analysis (where appropriate) in support of ultimate robotic precursor missions (Q32). ...
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Nearly half a century ago, two papers postulated the likelihood of lunar lava tube caves using mathematical models. Today, armed with an array of orbiting and fly-by satellites and survey instrumentation, we have now acquired cave data across our solar system—including the identification of potential cave entrances on the Moon, Mars, and at least nine other planetary bodies. These discoveries gave rise to the study of planetary caves. To help advance this field, we leveraged the expertise of an interdisciplinary group to identify a strategy to explore caves beyond Earth. Focusing primarily on astrobiology, the cave environment, geology, robotics, instrumentation, and human exploration, our goal was to produce a framework to guide this subdiscipline through at least the next decade. To do this, we first assembled a list of 198 science and engineering questions. Then, through a series of social surveys, 114 scientists and engineers winnowed down the list to the top 53 highest priority questions. This exercise resulted in identifying emerging and crucial research areas that require robust development to ultimately support a robotic mission to a planetary cave—principally the Moon and/or Mars. With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable. Subsequently, we will be positioned to robotically examine lunar caves and search for evidence of life within martian caves; in turn, this will set the stage for human exploration and potential habitation of both the lunar and martian subsurface.
... This work is part of an ongoing effort to map Titan at a global scale Malaska, Lopes, Hayes, et al., 2016;Schoenfeld et al., 2021) with the intention to comprehensively determine surface processes and evolutionary history of that world as well as an examination of potential initial characterization of planetary cave formation (Titus et al., 2021). We used mosaiced data sets of Synthetic Aperture Radar images (SAR; refer to Lopes et al., 2020 for details) collected with Cassini RADAR that were loaded into the ArcGIS™ 10.6 (ESRI) software package. ...
... On many bodies of interest in our solar system, caves and/or the deep subsurface represents a sequestered environment that is safe from ionizing radiation, thermally buffered, devoid of light, with physical properties that may allow different deposits to seep out of the walls (Wynne, Mylroie, et al., 2022;. For many bodies with harsh conditions, the subsurface can provide a potential astrobiological refuge prime for investigation (Titus et al., 2021;Wynne, Mylroie, et al., 2022). However, on Titan, the subsurface does not present a unique thermal or radiation-buffered environment relative to the open surface. ...
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We propose that cycling hydrocarbon rains on Saturn's moon Titan are likely to create subsurface conduits through dissolution geology of the extensive organic and largely‐soluble substrate. In this work we inventory different terrains and locations on Titan that could host potential subsurface access points or caves. Using Cassini data, we identified and enumerated a cryovolcanic construct, filled and empty lake basins that may have formed through karstic processes, estimates of closed valleys in organic plateaux, and enigmatic equatorial pits. Our preliminary survey identified over 21,000 estimated locations for future exploration to identify potential caves and cave forming processes on that world. We speculate that the exploration of these caves could teach us about the cave forming processes, as well as the past climate history and perhaps even chemical deposition history on Titan.
... Data processing with image elaboration and GIS software lead to vast opportunities in the geomorphological and geological fields, allowing detailed investigations to be carried out, which can be functional also to speleological research and karst sciences. These methods are also the only possible for detecting surface morphologies on other planetary bodies (e.g., Palafox et al., 2017;Wang et al., 2018;Silburt et al., 2019), and are actually used to find Candidate Cave Entrances (CCEs) for future robotic cave exploration missions on both the Moon and Mars (Cushing, 2012;Titus et al., 2021aTitus et al., , 2021b. ...
... Before setting foot on the Moon or Mars, a remote sensing inventory of CCEs should be acquired on potential landing sites, to target the most promising areas for future planetary cave exploration (Sauro et al., 2020;Titus et al., 2021aTitus et al., , 2021b. The most interesting potential extraterrestrial caves identified on Mars and the Moon are lava tubes, but it might be worth having a look also into the possible solutional caves in Fig. 13. ...
Article
The Cordillera de la Sal (CDS) is a NNE-SSW elongated fold-and-thrust belt several km wide and over 100 km long located in the hyper-arid climate of the Atacama Desert. This ridge contains important Oligocene-Miocene continental sediments including thick interbedded salt rock units which form extensive outcrops. Despite the rare occurrence of rain events, these salt rock beds host well-developed and scientifically interesting underground cave systems, perfectly adapted to the contemporary drainage network. The complete lack of vegetation makes this area a perfect analogue to extraterrestrial evaporite karst areas. A remote sensing analysis of 600 km² of Pleiades images (acquired in 2018 by courtesy of European Space Agency) at a spatial resolution of 0.5 m (panchromatic) and 2 m (RGB and near-infrared bands) and DTMs extracted from stereographic couples has allowed to map the lithological units, the drainage network, and the candidate cave entrances (CCEs) of most of the Cordillera de la Sal. The study area has been divided in eight morpho-structural units, based on our geological and geomorphological mapping. An Analytic Hierarchy Process (AHP) was used to classify the CCE potential of these karst zones into four classes: low, medium, high, and very high potential of finding new caves. This remote-sensing derived CCEs inventory has been ground truthed with two testing datasets (101 points): i) confronting the cave register based on explorations carried out prior to this analysis, and ii) with a field-based validation in completely unexplored areas. These ground-truthing methods support the quality and reliability of our remote sensing-derived CCEs, with accuracies of 71% and 83%, respectively. With this integrated remote-sensing and ground-truthing approach, we highlight that CCEs identification by image analysis and GIS processing appears reliable for speleological explorations in the CDS and might be a valuable tool also for objective decision-making in the search of caves and potential areas susceptible to karst formation on other planetary bodies.
... 71 Because most known or postulated caves are at relatively high elevations on Mars, future missions using current entry, descent and landing techniques will likely not choose landing sites in the vicinity of cave entrances. 72 Martian caves remain largely uncharacterized, but are thought to be one to three times more voluminous than Earth caves. 73 While thermal conditions within caves are unknown, a cave roof thickness greater than 1 to 2 m reduces the amplitude of the ground temperature variation during the day. ...
Article
Since the 1980s, national and international planetary protection policies have sought to avoid contamination by terrestrial organisms that could compromise future investigations regarding the origin or presence of Martian life. Over the last decade, the number of national space agencies planning, participating in, and undertaking missions to Mars has increased, and private-sector enterprises are engaged in activities designed to enable commercial missions to Mars. The nature of missions to Mars is also evolving to feature more diversity in purposes and technologies. As missions to Mars increase and diversify, national and international processes for developing planetary protection measures recognize the need to consider the interests of scientific discovery, commercial activity, and human exploration. The implications of these changes for planetary protection should be considered in the context of how much science has learned about Mars, and about terrestrial life, in recent years.
... If brought to other planets (e.g. Mars), subsurface missions could bring new insights into their geologic past as well as on their potential for supporting life in the environmentally protected undergrounds [5]. In contrast to traditional exploration missions where a team of operators and scientists controls one rover, SubT introduced the challenging requirement that only a single human supervisor can directly interface with the deployed multi-agent team in real-time and when Typically a deployment of 4 to 6 ground vehicles was targeted during SubT, but the number of agents is extendable (e.g., see A with 11 robots). ...
Preprint
Real-world deployment of new technology and capabilities can be daunting. The recent DARPA Subterranean (SubT) Challenge, for instance, aimed at the advancement of robotic platforms and autonomy capabilities in three one-year development pushes. While multi-agent systems are traditionally deployed in controlled and structured environments that allow for controlled testing (e.g., warehouses), the SubT challenge targeted various types of unknown underground environments that imposed the risk of robot loss in the case of failure. In this work, we introduce a video game-inspired interface, an autonomous mission assistant, and test and deploy these using a heterogeneous multi-agent system in challenging environments. This work leads to improved human-supervisory control for a multi-agent system reducing overhead from application switching, task planning, execution, and verification while increasing available exploration time with this human-autonomy teaming platform.
... Caves of the Coastal Range have also been studied as analogs of Martian caves, of which several have been detected up to date (Cushing et al., 2007;Cushing, 2017;Titus et al., 2021). In order to test whether phototrophic microorganisms (or its remnants) could be found inside caves on Mars, well protected from the outside radiation environment, but still close enough to nearby entrances in order to perform photosynthesis, one of such caves ( Figure 6A) was inspected north of the city of Antofagasta (Azua-Bustos et al., 2009). ...
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The Atacama Desert is by far the driest and oldest desert on Earth, showing a unique combination of environmental extremes (extreme dryness, the highest UV radiation levels on Earth, and highly saline and oxidizing soils), explaining why the Atacama has been largely investigated as a Mars analog model for almost 20 years. Based on the source and the amount of water available for life and its analogy with Mars, two ecosystems are of interest in the Atacama: its Coastal Range and the much drier hyperarid core, which we here review in detail. Members of the three domains of life have been found across these ecosystems living at the limit of habitability, suggesting the potential dry limits for each domain and also unveiling the highly patchy distribution of microbial life in its most extreme regions. The thorough study of the Atacama has allowed us to understand how life has adapted to its extreme conditions, the specific habitats that life occupies in each case (thus suggesting the most likely places in which to search for evidence for life on Mars), and the number of biosignatures detected across this desert. Also, the characterization of west-to-east transects across this desert has shown to be of significant value to understand the potential adaptations that Martian microorganisms may have followed in an ever-drying planet. All of this explains why the Atacama is actively used as the testing ground of the technologies (detection instruments, rovers, etc.) that were sent and will be sent to Mars. We also highlight the need to better inform the exact locations of the sites studied to understand general trends, the need to identify the true native microbial species of the Atacama, and the impact of climate change on the most arid and most Martian desert of Earth.
... There are several reasons for the interest in these underground features in space exploration and research ( [11], [12]). Subsurface cavities are shielded from radiation, micrometeorite bombardment, and particle implantation, along with having more stable thermal conditions ( [13]). ...
Article
Lava caves are the result of a geological process related to the cooling of basaltic lava flows. On the Moon, this process may lead to caves several kilometers long and diameters of hundreds of meters. Access to lava tubes can be granted through skylights, a vertical pit between the lava tube and the lunar surface. This represents an outstanding opportunity for long-term missions, for future permanent human settlements, and for accessing pristine samples of lava, secondary minerals and volatiles. Given this, the ESA launched a campaign through the Open Space Innovation Platform calling for ideas that would tackle the many challenges of exploring lava pits. Five projects, including Robocrane, were selected. Solar light and direct line of sight (for communications) with the lunar surface are not available inside lava tubes. This is a problem for any robot (or swarm of robots) exploring the lava tubes. Robocrane tackles both problems by deploying an element (called the Charging head, or CH) at the bottom of the skylight by means of a crane. This CH behaves as a battery charger and a communication relay for the exploring robots. The required energy is extracted from the crane’s solar panel (on the surface) and driven to the bottom of the skylight through an electrical wire running in parallel to the crane hoisting wire. Using a crane allows the system to deal with unstable terrain around the skylight rim and protect the wires from abrasion from the rocky surface and the pit rim. The charger in the CH is wireless so that the charging process can begin as soon as any of the robots get close enough to the CH. This avoids complex and time-consuming docking operations, aggravated by the skylight floor orography. The crane infrastructure can also be used to deploy the exploring robots inside the pit, reducing their design constraints and mass budget, as the robots do not need to implement their own self-deployment system. Finally, RoboCrane includes all the sensors and actuators for remote operation from a ground station. RoboCrane has been designed in a parametric tool so it can be dynamically and rapidly adjusted to input-variable changes, such as the number of exploring robots, their electrical characteristics, and crane reach, etc.
... The results of our work demonstrate that tri-stereo satellite images are suitable for the morphometric assessment of shadow-prone negative and positive landforms, and might also be used for the analysis of skylights and collapses on lava flows on the Moon and on Mars, where vegetation or human-built structures are completely lacking, as preparatory surveys for future robotic and human explorations of extraterrestrial caves [31][32][33]. ...
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Hundreds of large and deep collapse dolines dot the surface of the Quaternary basaltic plateau of Azrou, in the Middle Atlas of Morocco. In the absence of detailed topographic maps, the morphometric study of such a large number of features requires the use of remote sensing techniques. We present the processing, extraction, and validation of depth measurements of 89 dolines using tri-stereo Pleiades images acquired in 2018–2019 (the European Space Agency (ESA) © CNES 2018, distributed by Airbus DS). Satellite image-derived DEMs were field-verified using traditional mapping techniques, which showed a very good agreement between field and remote sensing measures. The high resolution of these tri-stereo images allowed to automatically generate accurate morphometric datasets not only regarding the planimetric parameters of the dolines (diameters, contours, orientation of long axes), but also for what concerns their depth and altimetric profiles. Our study demonstrates the potential of using these types of images on rugged morphologies and for the measurement of steep depressions, where traditional remote sensing techniques may be hindered by shadow zones and blind portions. Tri-stereo images might also be suitable for the measurement of deep and steep depressions (skylights and collapses) on Martian and Lunar lava flows, suitable targets for future planetary cave exploration.
... Motivated by lunar and planetary exploration [32,2], we consider the robotic exploration of large-scale and unknown subterranean environments. The increased coverage and redundancy offered by a team of robots can improve exploration performance, relative to a single robot. ...
Preprint
Multi-robot exploration of complex, unknown environments benefits from the collaboration and cooperation offered by inter-robot communication. Accurate radio signal strength prediction enables communication-aware exploration. Models which ignore the effect of the environment on signal propagation or rely on a priori maps suffer in unknown, communication-restricted (e.g. subterranean) environments. In this work, we present Propagation Environment Modeling and Learning (PropEM-L), a framework which leverages real-time sensor-derived 3D geometric representations of an environment to extract information about line of sight between radios and attenuating walls/obstacles in order to accurately predict received signal strength (RSS). Our data-driven approach combines the strengths of well-known models of signal propagation phenomena (e.g. shadowing, reflection, diffraction) and machine learning, and can adapt online to new environments. We demonstrate the performance of PropEM-L on a six-robot team in a communication-restricted environment with subway-like, mine-like, and cave-like characteristics, constructed for the 2021 DARPA Subterranean Challenge. Our findings indicate that PropEM-L can improve signal strength prediction accuracy by up to 44% over a log-distance path loss model.
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Integrated analyses of Thermal Emission Imaging System (THEMIS) IR, Context Camera (CTX), and Mars Orbiter Laser Altimeter (MOLA) data sets have been used to characterize the western flank of the Martian volcano Alba Mons, which hosts a prominent population of lava tube systems. Identification and mapping of lava tube systems is based on both morphologic and topographic analyses, including the presence of chains of collapse depressions and elongate, sinuous ridges. Lava tubes and adjacent tabular lava flows with lengths of 100⁺ km form an extensive lava flow field. Analyses of topographic data sets, including slope maps, suggest continuity of the radial flow field pattern across the full western flank. Concurrent surface activity across the western flank is consistent with age constraints from geologic mapping and crater size‐frequency distributions that indicate Early Amazonian ages. The mapped population of 331 lava tube systems in the western flank geologic map quadrangle has a mean length of 36.2 km and a total length of ∼12,000 km. Individual lava tube systems extend up to ∼400 km. Orientation and slope data for lava tube systems show small deviations compared to regional values in 50‐km grid cells defined by the MOLA Digital Elevation Model, suggesting a strong coupling of lava tubes to the current slopes of Alba Mons. Mapping of lava tube systems documents segments both showing collapse and with no collapse, indicating the potential for extensive subsurface cavities that would be important astrobiological targets.
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Lava tubes are a commonplace feature on the terrestrial planets, and knowledge of tube size and location informs lava flow processes. Future exploration of lava tubes on the Moon can provide access to geologic environments that likely remain unaltered from their emplacement billions of years ago. Lunar lava tubes may also provide astronauts protection from thermal extremes, meteoroid impacts, and radiation. High‐resolution magnetic identification and characterization of lava tubes can be used to help inform future scientific investigations of lava tubes for human exploration and utilization. We demonstrate how magnetometry is useful for determining the geometry and extent of lava tubes on the Earth and, by proxy, the Moon, by relating the magnetic anomalies produced by lava tubes to their location and geomorphology. Using a proton‐precession total field magnetometer, we surveyed an area of more than 100,000 m², with cross‐tube linear traverses spaced at 3–5 m, perpendicular to an approximately 1,000 m length of the Modoc Crater lava tube complex, within the Lava Beds National Monument (California, USA). The observed magnetic anomalies of the sections known as Incline, Skull, and Ship Caves are compared against synthetic predictions, and the sensitivity of the magnetic anomalies to the tube geometry used to derive a basic relationship between the two. We use our model of terrestrial lava tube magnetic anomalies and adjust for the lunar magnetic environment to predict the signature of anomalies resulting from tubes on the Moon.
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This work presents a field-hardened autonomous multimodal legged-aerial robotic system for subterranean exploration, extending a legged robot to be the carrier of an aerial platform capable of a rapid deployment in search-and-rescue scenarios. The driving force for developing such robotic configurations are the requirements for large-scale and long-term missions, where the payload capacity and long battery life of the legged robot is combined and integrated with the agile motion of the aerial agent. The multimodal robot is structured around the quadruped Boston Dynamics Spot, enhanced with a custom configured autonomy sensor payload as well as a UAV carrier platform, while the aerial agent is a custom built quadcopter. This work presents the novel design and hardware implementation as well as the onboard sensor suites. Moreover it establishes the overall autonomy architecture in a unified supervision approach while respecting each locomotion modality, including guidance, navigation, perception, state estimation, and control capabilities with a focus on rapid deployment and efficient exploration. The robotic system complete architecture is evaluated in real subterranean tunnel areas, in multiple fully autonomous search-and-rescue missions with the goal of identifying and locating objects of interest within the subterranean environment.
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Growing interest in studying large terrestrial lava tubes is motivated in part by their analogy with their extra‐terrestrial counterparts. However, on Earth, the formation of such structures is still poorly understood. Here, the lava tube system of La Corona (Lanzarote, Canary Islands, Spain) is studied to identify how pre‐existing stratigraphy can govern a lava tube's evolution. Combining terrestrial laser scanner technology with field observations and geochemical analyses of the pre‐existing lava enabled us to reconstruct the three‐dimensional geometry of the lava tube system, the paleo‐surface trough which it developed, and the volcanic series into which it carved its path. We show that a pyroclastic layer played a key role in the development of the lava tube. The layer—Derived from late Quaternary Strombolian activity—Is traceable along almost the full length of the tube path and defines the paleo‐topography. The excavation process mostly happens because of the mechanical strength of the substrate, that controls the widening of the growing lava tube. Other influential parameters controlling erosion include slope variations of the paleo‐surface (i.e., knickpoints), and the lava physical properties. Since weak layers such as regolith are a common feature of extra‐terrestrial lava flows, the processes seen at La Corona to the may be highly relevant to the development of planetary lava tube systems.
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Following the dramatic events of 2020, the year 2021 was marked by a slow recovery to prepandemic conditions. The previously deserted department building became populated again; students were finally allowed to attend lectures in class, conferences and meetings could be attended in person. In this third edition of the Yearbook of the Department of Geosciences, we wish to bring to light the numerous activities that we managed to organise and host during this transitional year, along with what we have learned from the pandemic period. First, a few numbers. In 2021, the Department of Geosciences counted 16 full professors, 30 associate professors and 12 researchers (including RU, RTDa ed RTDb), 44 postdoc and 47 PhD students. This staff provided teaching in 17 BSc and 35 MSc courses; however, our main commitment was devoted to the three courses hosted by the department, these being the BSc degree in Geological Sciences, the MSc degree in Geology and Technical Geology and the recently established MSc degree in Geophysics for Natural Risks and Resources. Altogether, these three degrees are attended by 287 students. Also in 2021, the pandemic called for restrictions on teaching activity that were especially limiting during the springtime. Laboratories and field activities, crucial elements in the education of young geoscientists, were partly impeded. Fortunately, the situation ameliorated in due course, and the new academic year provided the opportunity to start fresh. A total of 31 and 36 students received their degrees in Geological Sciences (BSc) and in Geology and Technical Geology (MSc), respectively, and 43 additional students were supervised by our researchers to obtain their degrees in other courses from other departments. High-quality research carried out at the department attracted graduate students from abroad: in 2021, 13 out of 45 postdocs and 6 out of 14 PhD students were foreign citizens. The department could rely on 34 research laboratories that yielded a huge number of sample preparations and analyses. Part of the research activities were supported by 56 research projects. The department also hosts CIRCe, which is the only centre in Italy for investigating cement materials and the formulation of construction binders. This centre not only collaborates with several companies and institutions at the national and international levels, but it is also involved in the training and support of African students and researchers and in consultancy for small companies in line with UNESCO’s Sustainable Development Goals. The efficiency of our laboratories, combined with successful activities in fundraising, allowed the department to develop and maintain a relevant number of collaborations, which are estimated to include more than 102 European and extra-European and 46 Italian universities, institutions and private companies. A total of 192 papers were published in 2021, and our department ranked first in Italy in the Nature Index international ranking, which is only based on the number of papers published in high-impact journals; we have the 92nd position in the world in terms of score. The department is also involved in the museum network of the University of Padua, thanks to its collection of Italian and foreign rocks, fossils and minerals housed in the Museum of Geology and Palaeontology and in the Museum of Mineralogy. Finally, the department has been actively committed to promoting and offering the dissemination and divulgation of scientific knowledge through TV and radio interviews and laboratories with local schools and exhibits. In total, more than 60 events were organised, such as the Night of the Research 2021, thus demonstrating the specific dedication of the department to outreach and communication.
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Robotic spacecraft have helped expand our reach for many planetary exploration missions. Most ground mobile planetary exploration robots use wheeled or modified wheeled platforms. Although extraordinarily successful at completing intended mission goals, because of the limitations of wheeled locomotion, they have been largely limited to benign, solid terrain and avoided extreme terrain with loose soil/sand and large rocks. Unfortunately, such challenging terrain is often scientifically interesting for planetary geology. Although many animals traverse such terrain at ease, robots have not matched their performance and robustness. This is in major part due to a lack of fundamental understanding of how effective locomotion can be generated from controlled interaction with complex terrain on the same level of flight aerodynamics and underwater vehicle hydrodynamics. Early fundamental understanding of legged and limbless locomotor-ground interaction has already enabled stable and efficient bio-inspired robot locomotion on relatively flat ground with small obstacles. Recent progress in the new field of terradynamics of locomotor-terrain interaction begins to reveal the principles of bio-inspired locomotion on loose soil/sand and over large obstacles. Multi-legged and limbless platforms using terradynamics insights hold the promise for serving as robust alternative platforms for traversing extreme extraterrestrial terrain and expanding our reach in planetary exploration.
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Robotic spacecrafts have helped expand the reach for many planetary exploration missions. Most ground mobile planetary exploration robots use wheeled or modified wheeled platforms. Although extraordinarily successful at completing intended mission goals, because of the limitations of wheeled locomotion, they have been largely limited to benign, solid terrain and avoided extreme terrain with loose soil/sand and large rocks. Unfortunately, such challenging terrain is often scientifically interesting for planetary geology. Although many animals traverse such terrain at ease, robots have not matched their performance and robustness. This is in major part due to a lack of fundamental understanding of how effective locomotion can be generated from controlled interaction with complex terrain on the same level of flight aerodynamics and underwater vehicle hydrodynamics. Early fundamental understanding of legged and limbless locomotor–ground interaction has already enabled stable and efficient bioinspired robot locomotion on relatively flat ground with small obstacles. Recent progress in the new field of terradynamics of locomotor–terrain interaction begins to reveal the principles of bioinspired locomotion on loose soil/sand and over large obstacles. Multilegged and limbless platforms using terradynamics insights hold the promise for serving as robust alternative platforms for traversing extreme extraterrestrial terrain and expanding the reach in planetary exploration. Although very successful for planetary exploration, wheeled rovers are largely limited to benign, solid extraterrestrial terrain. Recent progress in the new field of terradynamics, which describes how locomotion emerges from interaction with complex terrain, provides the foundation for enabling biologically inspired robots to robustly traverse a broader range of geologically interesting extreme terrain with loose soil, sand, and large rocks. Image credit for Mars terrain: NASA/JPL‐Caltech.
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Sinuous collapse chains and skylights in lunar and Martian volcanic regions have often been interpreted as collapsed lava tubes (also known as pyroducts). This hypothesis has fostered a forty years debate among planetary geologists trying to define if analogue volcano-speleogenetic processes acting on Earth could have created similar subsurface linear voids in extra-terrestrial volcanoes. On Earth lava tubes are well known thanks to speleological exploration and mapping in several shield volcanoes, with examples showing different genetic processes (inflation and overcrusting) and morphometric characters. On the Moon subsurface cavities have been inferred from several skylights in Maria smooth plains and corroborated using gravimetry and radar sounder, while on Mars several deep skylights have been identified on lava flows with striking similarities with terrestrial cases. Nonetheless, the literature on this topic is scattered and often presents inaccuracies in terminology and interpretation. A clear understanding of the potential morphologies and dimensions of Martian and lunar lava tubes remains elusive. Although it is still impossible to gather direct information on the interior of Martian and lunar lava tube candidates, scientists have the possibility to investigate their surface expression through the analysis of collapses and skylight morphology, morphometry and their arrangement, and compare these findings with terrestrial analogues. In this review the state of the art on terrestrial lava tubes is outlined in order to perform a morphological and morphometric comparison with lava tube candidate collapse chains on Mars and the Moon. By comparing literature and speleological data from terrestrial analogues and measuring lunar and Martian collapse chains on satellite images and digital terrain models (DTMs), this review sheds light on tube size, depth from surface, eccentricity and several other morphometric parameters among the three different planetary bodies. The dataset here presented indicates that Martian and lunar tubes are 1 to 3 orders of magnitude more voluminous than on Earth, and suggests that the same processes of inflation and overcrusting were active on Mars, while deep inflation and thermal entrenchment was the predominant mechanism of emplacement on the Moon. Even with these outstanding dimensions (with total volumes exceeding 1 billion of m³), lunar tubes remain well within the roof stability threshold. The analysis shows that aside of collapses triggered by impacts/tectonics, most of the lunar tubes could be intact, making the Moon an extraordinary target for subsurface exploration and potential settlement in the wide protected and stable environments of lava tubes.
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The Cassini/Huygens mission revealed a terrain type on Saturn's moon Titan of dissected, elevated plateaux with a high density of valleys named labyrinth terrain. We define four subtypes of labyrinth terrains: valleyed, polygonal, finely-dissected, and the possible outlier Kronin Labyrinth. We mapped the locations of all labyrinths imaged by Cassini and found they are distributed preferentially at high latitudes. We characterize the labyrinths by morphometric parameters such as intervalley width, valley width, and percent valleys. We find many labyrinths contain closed valleys, which constrains their formation and evolution. We also examine their low microwave emissivity spectral characteristics and find that the labyrinths are consistent with a bulk composition of dominantly organic materials, with some component of water ice – characteristics similar to Titan's undifferentiated plains. Our analyses show that labyrinths are ancient terrains – only the mountains and hummocky terrains are older. This implies that significant organic production occurred early in Titan's history. The organic inventory represented by the labyrinths is estimated to be 15–42% of the solid organic inventory of Titan (or 14–35% of the total surface organics, if the hydrocarbons of the lakes and seas are also included). Our preferred formation of the labyrinth terrains is erosion through dissolution and fluvial processes that dissect the plateau in a manner similar to dissolution geology (karst) on Earth. This scenario requires that the organics that make up the labyrinth terrain be soluble in methane and/or ethane liquids. It also suggests that the origin of the plateaux may have derived from Titan's past chemical production and subsequent depositional record.
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We present the first comprehensive examination of the geysering, tidal stresses, and anomalous thermal emission across the south pole of Enceladus and discuss the implications for the moon's thermal history and interior structure. A 6.5 yr survey of the moon's south polar terrain (SPT) by the Cassini imaging experiment has located ~100 jets or geysers erupting from four prominent fractures crossing the region. Comparing these results with predictions of diurnally varying tidal stresses and with Cassini low resolution thermal maps shows that all three phenomena are spatially correlated. The coincidence of individual jets with very small (~10 m) hot spots detected in high resolution Cassini VIMS data strongly suggests that the heat accompanying the geysers is not produced by shearing in the upper brittle layer but rather is transported, in the form of latent heat, from a sub-ice-shell sea of liquid water, with vapor condensing on the near-surface walls of the fractures. Normal stresses modulate the geysering activity, as shown in the accompanying paper; we demonstrate here they are capable of opening water-filled cracks all the way down to the sea. If Enceladus' eccentricity and heat production are in steady state today, the currently erupting material and anomalous heat must have been produced in an earlier epoch. If regional tidal heating is occurring today, it may be responsible for some of the erupting water and heat. Future Cassini observations may settle the question.
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This paper presents newly discovered candidate cave entrances into Martian near-surface lava tubes, volcano-tectonic fracture systems, and pit craters and describes their characteristics and exploration possibilities. These candidates are all collapse features that occur either intermittently along laterally continuous trench-like depressions or in the floors of sheer-walled atypical pit craters. As viewed from orbit, locations of most candidates are visibly consistent with known terrestrial features such as tube-fed lava flows, volcano-tectonic fractures, and pit craters, each of which forms by mechanisms that can produce caves. Although we cannot determine subsurface extents of the Martian features discussed here, some may continue unimpeded for many kilometers if terrestrial examples are indeed analogous. The features presented here were identified in images acquired by the Mars Odyssey's Thermal Emission Imaging System visiblewavelength camera, and by the Mars Reconnaissance Orbiter's Context Camera. Select candidates have since been targeted by the High-Resolution Imaging Science Experiment. Martian caves are promising potential sites for future human habitation and astrobiology investigations; understanding their characteristics is critical for long-term mission planning and for developing the necessary exploration technologies.
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