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A roadmap for planetary caves science and exploration
... 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. ...
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). ...
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.
... Remotely piloted drones will be useful for characterization and limited exploration (for example, examination of entrances to potentially identify lateral passages), while rover and other robotic assets can ultimately be used for exploration. Refer to Titus, Wynne, Malaska, and others (2021) and Wynne, Titus, Agha-Mohammadi, and others (2022) for additional details. Figure modified from Titus, Wynne, Malaska, and others (2021). Individual images of planetary bodies from NASA/JPL-Caltech. ...
... Remotely piloted drones will be useful for characterization and limited exploration (for example, examination of entrances to potentially identify lateral passages), while rover and other robotic assets can ultimately be used for exploration. Refer to Titus, Wynne, Malaska, and others (2021) and Wynne, Titus, Agha-Mohammadi, and others (2022) for additional details. Figure modified from Titus, Wynne, Malaska, and others (2021). Individual images of planetary bodies from NASA/JPL-Caltech. ...
On Earth, caves are unique environments at the intersection of geology, climate, and biology. Given that the same terrestrial speleogenetic processes exist throughout the solar system, it would be surprising if caves beyond Earth did not exist. Thousands of potential cave entrances (or subsurface access points) have been identified from Earth’s Moon to Pluto’s moon, Charon. To date, our most comprehensive knowledge of these potential subsurface access points is for the Moon, Mars, and Titan, which collectively contain more than 20,000 features. Missions are either ongoing or planned for these three planetary bodies. One of these missions may ultimately detect a cave and potentially confirm it contains a laterally trending passage.
... The protective properties of these environments have also been suggested for Martian lava tubes, formed in volcanic regions from the ancient times of the Noachian period up to just a few hundred of million years ago 25 . These planetary caves might preserve biosignatures, which could be crucial in understanding past or present biological processes on Mars 2,26,27 . Similarly, the study by Benison et al. 28 on depositional and diagenetic sulfates in Jezero Crater on Mars, highlights the preservation potential of sulfate minerals in capturing environmental conditions and possible biosignatures from past Martian surface and groundwater interactions. ...
... The lipid composition of MCPF samples (MCPF01, MCPF03, and MCPF05) reveals distinct patterns for each sample (Fig. 4D). MCPF01 exhibits a bimodal distribution of n-alkanes, with peaks at C 15 and C 27 . This distribution, observed in previous studies on organic fractions from complex environmental matrices such as soil and sediments 43,44,68 , indicates two distinct carbon pools associated with microbial activity (nalkanes <C 20 ) and vegetational biomass (epicuticular waxes, n-alkanes >C 21 ). ...
Exploring molecular biomarkers in lava tube speleothems offers insights into environmental dynamics, biogeochemical processes, and subsurface life, with implications for astrobiology, particularly in Martian analog environments. Despite extensive biomarker research in marine and terrestrial settings, lava tube studies are limited. This study employed molecular, isotope and mineralogical characterization to analyze sulfate speleothems from six lava tubes of Lanzarote (Canary Islands), considered analog for the Moon and Mars. The combination of mass spectrometry, thermogravimetry, and mineralogical techniques, revealed geological processes, biomarkers and their biological sources. The identified minerals were primarily calcium and sodium sulfates. Sulfur isotope analyses indicated volcanic and oceanic origins, while carbon isotope composition and pyrolysis analyses suggested influences from vegetation and microbial activity. Lipidic profiles highlighted branched and n-alkanes, as well as palmitic and stearic acid methyl esters, suggesting microbial origins. These findings contribute to understanding geological and environmental dynamics in lava tubes and recognizing potential biosignatures on Earth and other planets.
... There are many possible missions for cave exploration on other planets. A roadmap has been suggested by Titus et al. (2021) that when it comes to stage (2) characterization (surface operations) and (3) exploration (subsurface operations), that activities build upon stage (1) where potential cave entrances have been uncovered using remote context imaging [25]. Such activities focus on mitigating risk of subsurface exploration by mapping out detailed architectures and models. ...
... There are many possible missions for cave exploration on other planets. A roadmap has been suggested by Titus et al. (2021) that when it comes to stage (2) characterization (surface operations) and (3) exploration (subsurface operations), that activities build upon stage (1) where potential cave entrances have been uncovered using remote context imaging [25]. Such activities focus on mitigating risk of subsurface exploration by mapping out detailed architectures and models. ...
As space agencies around the world look to further explore the Moon and Mars, the role of robots is becoming increasingly important in navigating harsh space environments that pose threats to humans. Subsurface environments such as lava tubes and caves have been found to exist on both the Moon and Mars. Due to their subterranean nature, potential astro-microbial life could be sheltered from the harsh surface radiation conditions. Therefore, subsurface environments may contain valuable scientific and resource information about biochemical signatures and geophysical activities that could inform past or present signs of extra-terrestrial life. However, these subsurface environments present new challenges different from exploring surface terrains. Firstly, navigating relatively unknown terrain and geological structures requires robots to be more adaptable with higher independence and autonomous decision-making. Secondly, with no direct line of sight to the surface, communication signals are attenuated limiting data bandwidth and may require a physical data wire to the cave entrance. Furthermore, the lack of sunlight in subsurface exploration imposes power constraints as solar power cannot be directly utilized. As cave exploration on Earth has been used as analogues for space missions and has dealt with similar challenges, the robotic technologies and methods used to access terrestrial caves may prove useful for exploring planetary caves. This paper aims to investigate the potential of using current robotic technologies developed for cave exploration on Earth, towards exploring the subsurface on the Moon and Mars. It will first review current exploration technologies such as Unmanned Aerial Vehicles (UAV), Unmanned Ground Vehicles (UGV) and other robotic platforms. From this, key underpinning technologies will be identified. The technology readiness level of these technologies will be assessed against the unique characteristics of lunar and Martian subsurface environments. Finally, this will enable a more thorough understanding around the feasibility and readiness of these different robotic platforms for planetary cave exploration. The paper concludes with suggestions for further areas of development and testing to help inform, validate, and prepare for subsurface exploration on other celestial bodies.
... 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. ...
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. ...
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.
... Throughout history, humans have sought shelter in caves to resist external influences, and similarly, natural caves on extraterrestrial planets can provide initial shelters for humans [5]. In recent years, with the rapid advancement of observation technologies, research on planetary caves has experienced substantial growth, and the exploration and utilization of extraterrestrial caves are in a golden age of scientific discovery [6][7][8]. ...
The Moon, as the closest celestial body to Earth, plays a pivotal role in the progression of deep space exploration, and the establishment of research outposts on its surface represents a crucial step in this mission. Lunar lava tubes are special underground caves formed by volcanic eruptions and are considered as ideal natural shelters and scientific laboratories for lunar base construction. This paper begins with an in-depth overview of the geological origins, exploration history, and distribution locations of lunar lava tubes. Subsequently, it delves into the presentation of four distinctive advantages and typical concepts for constructing bases within lava tubes, summarizing the ground-based attempts made thus far in lunar lava tube base construction. Field studies conducted on a lava tube in Hainan revealed rock compositions similar to those found during the Apollo missions and clear lava tube structures, making it a promising analog site. Lastly, the challenges and opportunities encountered in the field of geotechnical engineering regarding the establishment of lunar lava tube bases are discussed, encompassing cave exploration technologies, in-situ testing methods, geomechanical properties under lunar extreme environments, base design and structural stability assessment, excavation and reinforcement techniques, and simulated Earth-based lava tube base.
... While there are still challenges for EDL at high altitudes on Mars (where caves are observed from orbit [3]), there have been advances in robotic mobility and autonomous navigation that make a cave exploration mission a J o u r n a l P r e -p r o o f Journal Pre-proof viable option for near-future robotic deployment on Mars. The potential success of such missions could shed light both on Mars' geologic past as well as its potential for supporting life [4]. ...
... This would result in a substantial advancement in the understanding of planetary volcanism 25 . The presented work also implies that SAR imaging is a viable methodology for characterizing and assessing the accessibility of lunar conduits extending from pit entrances 26 . The work presented here could be substantially expanded if radar orbital sensors with a resolution able to resolve the interior of all lunar pits identified by LRO 6 are deployed in lunar orbit. ...
Several potential subsurface openings have been observed on the surface of the Moon. These lunar pits are interesting in terms of science and for potential future habitation. However, it remains uncertain whether such pits provide access to cave conduits with extensive underground volumes. Here we analyse radar images of the Mare Tranquillitatis pit (MTP), an elliptical skylight with vertical or overhanging walls and a sloping pit floor that seems to extend further underground. The images were obtained by the Mini-RF instrument onboard the Lunar Reconnaissance Orbiter in 2010. We find that a portion of the radar reflections originating from the MTP can be attributed to a subsurface cave conduit tens of metres long, suggesting that the MTP leads to an accessible cave conduit beneath the Moon’s surface. This discovery suggests that the MTP is a promising site for a lunar base, as it offers shelter from the harsh surface environment and could support long-term human exploration of the Moon.
... As noted earlier, planetary caves and lava tubes are among the most promising geological and astrobiological targets in the solar system (59)(60)(61)(62). Given that martian lava tubes are of particular interest (1,63) it was decided that a field test of ReachBot technology should be conducted in a reasonable analog on Earth. ...
Caves and lava tubes on the Moon and Mars are sites of geological and astrobiological interest but consist of terrain that is inaccessible with traditional robot locomotion. To support the exploration of these sites, we present ReachBot, a robot that uses extendable booms as appendages to manipulate itself with respect to irregular rock surfaces. The booms terminate in grippers equipped with microspines and provide ReachBot with a large workspace, allowing it to achieve force closure in enclosed spaces such as the walls of a lava tube. To propel ReachBot, we present a contact-before-motion planner for non-gaited legged locomotion that utilizes internal force control, similar to a multi-fingered hand, to keep its long, slender booms in tension. Motion planning also depends on finding and executing secure grips on rock features. We use a Monte Carlo simulation to inform gripper design and predict grasp strength and variability. Additionally, we use a two-step perception system to identify possible grasp locations. To validate our approach and mechanisms under realistic conditions, we deployed a single ReachBot arm and gripper in a lava tube in the Mojave Desert. The field test confirmed that ReachBot will find many targets for secure grasps with the proposed kinematic design.
... Diverse cave formations exist on Earth, including Melt formation caves, Lava tubes, Glacier caves, Fracture caves, Erosional caves, Sea caves, Wind-scoured and Canyon rock shelters, etc. Similarly, Mars may host various types of caves, offering habitats conducive to life and indicating a strong likelihood of subsurface microbial ecosystems [228,229,230]. ...
The cosmos, replete with the elemental diversity of Earth, continues to cloak the existence of extraterrestrial life in mystery. Vital to the search for life is the identification of environments that can support biological processes. This review synthesizes current knowledge on the conditions necessary for life, with a special focus on extremophiles. These organisms, thriving under extreme conditions, illustrate the robust adaptability required for life beyond Earth. We examine the evolutionary adaptations on Earth to provide a framework for potential analogues on other celestial bodies. Importantly, this paper reports the initial identification of approximately three hundred three (∼ 303) sites on Mars as potential habitats intriguingly considered as potential Mars Cave Candidates (MCC) based on meticulous visual interpretations, and require detailed investigation to confirm their nature, whether as caves, other geological features, or craters. These investigations are currently ongoing, highlighting the dynamic and exploratory nature of Martian research. The findings are preliminary and serve to inform the development of robotic exploration strategies aimed at in-depth study of these environments, thereby advancing the astrobiological search for life. This review sets strategic directions for future research, aiming to refine our approach to uncovering where and how life could exist across the cosmos. By guiding future missions, both robotic and astrobiological, this work seeks to deepen our understanding of potential extraterrestrial habitats and to foster a systematic exploration of these promising sites.
... The growing interest for lunar exploration intensifies the scientific interest in lunar lava tubes in recent years across a wide range of disciplines (e.g., Shaw et al., 2021;Titus et al., 2021;Viudez-Moreiras, 2021;Ding et al., 2022;Miaja et al., 2022;Stupar et al., 2022;Song et al., 2023;Zhu et al., 2024). And naturally, it follows that the planning of any human or robotic activity in lunar lava tubes will require careful investigation of their stability and safety. ...
This paper provides detailed numerical analyses of lunar lava tubes stability, where for the first time variability in cross-section geometries is considered. A novel approach included a dedicated procedure for extracting characteristics needed for random geometry generation together with the demonstration of its usage. Stability analyses were performed with finite element limit analysis (FELA) which is found to be very effective for analyzing tens of thousands of realizations. The FELA method provides collapse geometries that were examined to constrain the relations between the collapse size extent and width of the lava tube. New findings on types and sizes of lunar lava tube roof collapses were obtained, and they are the first step toward making stability analysis more realistic for future human and robotic exploration of lunar lava tubes. The results allow us to constrain the approximate widths of the lunar tube beneath skylights to be 300 m, as observed for the assumed rock parameters. In addition, the probabilistically based analyses allow to show that thin roofs (< 10 m) are very unlikely to be stable for the tubes of a few hundred meters in width under lunar conditions, and that the gravity trigger failures are more probable on the Moon when considering variations in lava tube geometry than for the previously considered cases of elliptical and circular shapes.
... More than 1200 potential volcanic cave entrances have been identified using Mars orbiter data [1,2]. One of these may, in the near future, provide the most direct access to the Martian subsurface in the search for signs of past or extant life, water ice, or shelter for future human habitats [3][4][5]. Lava tube caves are among the different types of terrestrial analog sites that have been proposed as proxies for Martian environments where biosignatures might be preserved [4,6,7]. We have been preparing for a future mission to a Martian cave, practicing with wheeled and legged robots equipped with scientific and autonomy platforms deployed in lava tubes on Earth. ...
Volcanic caves on Mars are environments that provide near-surface shelter, serving as ideal sites for the search for signs of past or extant life as well as potential habitats for future manned missions. The BRAILLE (Biologic and Resource Analog Investigations in Low Light Environments) project is a multi-year field research program that has conducted mission operations within terrestrial analog sites at Lava Beds National Monument (USA) to test the potential for instrumented robots to autonomously map and characterize volcanic caves. The field tests have involved both wheeled and legged robotic platforms, and have leveraged the NeBula (Networked Belief-aware Perceptual Autonomy) autonomy framework that has been developed by JPL. Robot-based surveys have been complemented by investigations conducted by BRAILLE scientists to characterize microbial communities in terrestrial lava caves, distinguish secondary minerals that can serve as persistent geologic signatures of these communities, and test a variety of sensors that can be used to detect these features. Concepts of operations have been implemented through a series of field tests using single and paired robots and with autonomous and waypoint-guided operations to test the ability of the instrumented robots to detect and provide detailed imaging of science analog targets.
... Furthermore, such autonomous robotic platforms mainly rely on their onboard perception systems in GNSS-denied environments such as Sub-T and extra-terrestrial sub-surfaces [5] for Simultaneous Localization and Mapping (SLAM). To ensure operational safety in such hazardous environments, a This work has been partially funded by the European Unions Horizon 2020 Research and Innovation Programme under the Grant Agreement No. 101003591 NEX-GEN SIMS. ...
Search and Rescue (SAR) missions in harsh and unstructured Sub-Terranean (Sub-T) environments in the presence of aerosol particles have recently become the main focus in the field of robotics. Aerosol particles such as smoke and dust directly affect the performance of any mobile robotic platform due to their reliance on their onboard perception systems for autonomous navigation and localization in Global Navigation Satellite System (GNSS)-denied environments. Although obstacle avoidance and object detection algorithms are robust to the presence of noise to some degree, their performance directly relies on the quality of captured data by onboard sensors such as Light Detection And Ranging (LiDAR) and camera. Thus, this paper proposes a novel modular agnostic filtration pipeline based on intensity and spatial information such as local point density for removal of detected smoke particles from Point Cloud (PCL) prior to its utilization for collision detection. Furthermore, the efficacy of the proposed framework in the presence of smoke during multiple frontier exploration missions is investigated while the experimental results are presented to facilitate comparison with other methodologies and their computational impact. This provides valuable insight to the research community for better utilization of filtration schemes based on available computation resources while considering the safe autonomous navigation of mobile robots.
... The Moon is the nearest celestial body to the Earth (Heiken et al., 1991;Badescu and Zacny 2015) and contains abundant energy and mineral resources that are extremely important for the sustainable development of human society. Lunar regolith exploration is the most direct and effective means of understanding the composition, formation, and evolution of the Moon to answer some fundamental scientific questions (Stamenković et al., 2019;Titus et al., 2021;Carlson 2019;Lin et al., 2022). In addition, it forms an essential prerequisite for trafficability assessments, infrastructure construction, and mineral resource exploitation and utilization necessary for establishing a permanent base for scientific research or settlements for human migration and interplanetary voyages (Zacny et al., 2010;Ding et al., 2022b;Zhang et al., 2021a). ...
On December 2, 2020, a 2-m class robotic drill onboard the Chinese Chang’E 5 lunar lander successfully penetrated 1 m into the lunar regolith and collected 259.72 g of samples. This paper presents the design and development, terrestrial tests, and lunar sampling results of the robotic drill. First, the system design of the robotic drill, including its engineering objectives, drill configuration, drilling and coring methods, and rotational speed determination, was studied. Subsequently, a control strategy was proposed to address the geological uncertainty and complexity of the lunar surface. Terrestrial tests were conducted to assess the sampling performance of the robotic drill under both atmospheric and vacuum conditions. Finally, the results of drilling on the lunar surface were obtained, and the complex geological conditions encountered were analyzed. The success of the Chinese Chang’E 5 lunar sample-return mission demonstrates the feasibility of the proposed robotic drill. This study can serve as an important reference for future extraterrestrial robotic regolith-sampling missions.
... In order to advance this technology further to make it a viable option for future planetary flight projects, AOTF-based NIR spectrometers would need to undergo additional demonstrations in a broader range of cave environments analogous to those we might expect on other solar system bodies, such as those described in Boston (2004). They would also need to be subjected to standard environmental tests such as thermal cycling and vibration testing to ensure that such an instrument could survive the rigors of launch, deep space travel, and entry, descent and landing (Titus et al., 2021). Finally, further miniaturization could be explored, for example, by making the optical design more compact, although given the compactness and low SWaP of PASA-L this is likely to only provide incremental improvement. ...
Planetary caves are desirable environments for the search for biosignatures corresponding to extant or extinct extraterrestrial life due to the protection they offer from surface-level solar radiation and ionizing particles. Near-infrared (NIR) reflectance spectroscopy is one of a multitude of techniques that, when taken together, can provide a comprehensive understanding of the geomicrobiology in planetary subsurface regions. To that end, we developed two portable NIR spectrometers that employ acousto-optic tunable filters and demonstrated them in three geochemically distinct cave environments. The instruments were deployed both as stand-alone spectrometers positioned against the targets manually and as a component of an instrument payload mounted on a quadruped robot capable of vertical excursions of several meters. In situ measurements of calcium carbonates, sulfates, metal oxides, and microbial colonies and mats revealed spectral signatures that enable a distinction between the targets of interest and the underlying substrates. The ruggedness and portability of the instruments, and their low size, weight, and power, spectral agility, and active illumination make AOTF-based spectrometers ideally suited for studies of planetary caves.
... 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. ...
... 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. ...
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.
... 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). ...
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.
... 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. ...
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.
... 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). ...
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]). ...
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]. ...
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.
ReachBot is a robot concept for the planetary exploration of caves and lava tubes, which are often inaccessible with traditional robot locomotion methods. It uses extendable booms as appendages, with grippers mounted at the end, to grasp irregular rock surfaces and traverse these difficult terrains. We have built a partial ReachBot prototype consisting of a single boom and gripper, mounted on a tripod. We present the details on the design and field test of this partial ReachBot prototype in a lava tube in the Mojave Desert. The technical requirements of the field testing, implementation details, and grasp performance results are discussed. The planning and preparation of the field test and lessons learned are also given.
Caves and lava tubes on the Moon and Mars are sites of geological and astrobiological interest but consist of terrain that is inaccessible with traditional robot locomotion. To support the exploration of these sites, we present ReachBot, a robot that uses extendable booms as appendages to manipulate itself with respect to irregular rock surfaces. The booms terminate in grippers equipped with microspines and provide ReachBot with a large workspace, allowing it to achieve force closure in enclosed spaces, such as the walls of a lava tube. To propel ReachBot, we present a contact-before-motion planner for nongaited legged locomotion that uses internal force control, similar to a multifingered hand, to keep its long, slender booms in tension. Motion planning also depends on finding and executing secure grips on rock features. We used a Monte Carlo simulation to inform gripper design and predict grasp strength and variability. In addition, we used a two-step perception system to identify possible grasp locations. To validate our approach and mechanisms under realistic conditions, we deployed a single ReachBot arm and gripper in a lava tube in the Mojave Desert. The field test confirmed that ReachBot will find many targets for secure grasps with the proposed kinematic design.
Despite contending with constraints imposed by the environment, morphology, and physiology, animals move well by physically interactingwith the environment to use and transition between modes such as running, climbing, and self-righting. By contrast, robots struggle to do so in real world. Understanding the principles of how locomotor transitions emerge from constrained physical interaction is necessary for robots to move robustly using similar strategies. Recent studies discovered that discoid cockroaches use and transition between diverse locomotor modes to traverse beams and self-right on ground. For both systems, animals probabilistically transitioned between modes via multiple pathways, while its self-propulsion created kinetic energy fluctuation. Here, we seek mechanistic explanations for these observations by adopting a physics-based approach that integrates biological and robotic studies. We discovered that animal and robot locomotor transitions during beam obstacle traversal and ground self-righting are barrier-crossing transitions on potential energy landscapes. Whereas animals and robot traversed stiff beams by rolling their body betweenbeam, they pushed across flimsy beams, suggesting a concept of terradynamic favorability where modes with easier physical interaction are more likely to occur. Robotic beam traversal revealed that, system state either remains in a favorable mode or transitions to one when energy fluctuation is comparable to the transition barrier. Robotic self-righting transitions occurred similarly and revealed that changing system parameters lowers barriers over which comparable fluctuation can induce transitions. Thetransitionsof animalsin both systems mostly occurred similarly, but sensory feedback may facilitate its beam traversal. Finally, we developed a method to measure animal movement across large spatiotemporal scales in a terrain treadmill.
Subterranean environments on Earth serve as an analog for the study of microbes on other planets, which has become an active area of research. Although it might sound contradictory that photosynthetic cyanobacteria thrive in extreme low light environments, they are frequent inhabitants of caves on Earth. Throughout the phylum these cyanobacteria have developed unique adaptations that cannot only be used for biotechnological processes but also have implications for astrobiology. They can, for example, both accommodate for the low light conditions by producing specific pigments that allow photosynthesis in near-infrared (IR) radiation/far-red light, and they can synthesize bioplastic compounds and calcium carbonate sheaths which represent valuable resources during human colonization of other planets or rock bodies. This article will highlight the potential benefits of cave-inhabiting cyanobacteria and will present a suitable bioreactor technique for the utilization of these special microbes during future space missions.
We introduce a dynamically deployed communication network (DDCN) paradigm using mesh topology in support of a distributed robotic multi-agent approach for the autonomous exploration of subsurface environments, i.e., caves, lava tube caves, lakes, and oceans, etc. The DDCN, comprising wireless communication beacons autonomously deployed via a rover or submersible in a Hansel & Gretel-inspired breadcrumb style, allows for the longest and most robust communication link between subterranean robotic agent(s) within, e.g., a lave tube cave or a subsurface ocean, and associated surface-borne robotic agent(s). Moreover, we briefly touch on the development of a robotic testbed and wired/wireless communication beacons in support of such astrobiological surface/subsurface exploration scenarios. Candidate lava tube caves have been identified on the Moon and Mars, raising possibilities for planetary exploration, astrobiology, habitat construction for future astronauts, and potential mining operations. Subterranean caverns, and in particular relatively deep lava tube caves, provide a possible refuge for life under otherwise challenging planetary surface conditions, and, as such, are of prime astrobiological relevance. Lava tube caves or other subsurface environments may also be suitable habitats for astronauts and subsequent human settlement but are yet to be explored in part due to difficulties ensuring continued communication with a robotic probe inside these environments. Moreover, the existence of subsurface oceans on ocean worlds, such as Europa, Enceladus, and Titan, has been backed by varying levels of evidence since the 1980s, though there has been no confirmation, i.e., direct observation, thus far. Such environments are also shielded from radiation, and, in combination with the hypothesized presence of water, are additional candidate environments for finding extant or fossilized life. The DDCN paradigm introduced herein directly addresses NASA's Space Technology Grand Challenges - "All Access Mobility" by enabling the most unconstrained exploration of subsurface environments through a dynamic communication network which ensures transmission of data from and possibly commands to the subsurface robotic probe. 2023 COSPAR. Published by Elsevier B.V. All rights reserved.
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.
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.
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.
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.
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.
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.
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.
NASA's GRAIL mission employed twin spacecraft in polar orbits around the Moon to measure the lunar gravity field at unprecedentedly high accuracy and resolution. The low spacecraft altitude in the extended mission enables the detection of small-scale surface or subsurface features. We analyzed these data for evidence of empty lava tubes beneath the lunar maria. We developed two methods, gradiometry and cross correlation, to isolate the target signal of long, narrow, sinuous mass deficits from a host of other features present in the GRAIL data. Here we report the discovery of several strong candidates that are either extensions of known lunar rilles, collocated with the recently discovered “skylight” caverns, or underlying otherwise unremarkable surfaces. Owing to the spacecraft polar orbits, our techniques are most sensitive to east-west trending near-surface structures and empty lava tubes with minimum widths of several kilometers, heights of hundreds of meters, and lengths of tens of kilometers.
This paper presents a new mission concept for planetary exploration, based on the deployment of a large number of small spherical mobile robots (“microbots”) over vast areas of a planet’s surface and subsurface, including structures such as caves and near‐surface crevasses (see Figure 1). This would allow extremely large‐scale in situ analysis of terrain composition and history. This approach represents an alternative to rover and lander‐based planetary exploration, which is limited to studying small areas of a planet’s surface at a small number of sites. The proposed approach is also distinct from balloon or aerial vehicle‐based missions, in that it would allow direct in situ measurement. In the proposed mission, a large number (i.e. hundreds or thousands) of cm‐scale, sub‐kilogram microbots would be distributed over a planet’s surface by an orbital craft and would employ hopping, bouncing and rolling as a locomotion mode to reach scientifically interesting artifacts in very rugged terrain. They would be powered by high energy‐density polymer “muscle” actuators, and equipped with a suite of miniaturized imagers, spectrometers, sampling devices, and chemical detection sensors to conduct in situ measurements of terrain and rock composition, structure, etc. Multiple microbots would coordinate to share information, cooperatively analyze large portions of a planet’s surface or subsurface, and provide context for scientific measurements. © 2005 American Institute of Physics
Terrestrial caves offer scientific and engineering insights and serve as testing grounds for future forays by humans and robots into caves on other worlds.
https://eos.org/science-updates/planetary-cave-exploration-progresses
This paper presents new field and synthetic modelling results of Electrical Resistivity Tomography (ERT) surveys for the identification and detection of lava tubes with the particular aim of using ERT tech-niques for stratigraphic investigations of planetary volcanic analogues. These geophysical surveys were undertaken at the Corona volcano (Lanzarote, Canary Islands), as part of the PANGAEA-X 2017 campaign, which formed part of the European Space Agency's (ESA) astronaut training program. ERT profiles were acquired at two test sites located along the main Corona lava tube system. During the campaign a variety of experimental setups were tested. This provided an ideal opportunity to cross-validate geophysical results with ground truth provided by partial surface exposure of the lava tubes and laser scanner mapping of the lava tube system in the subsurface. It also permitted an assessment of the usability of ERT in detecting lava tubes in a heterogeneous volcanic setting. Our experiments showed that a combination of different electrode arrays and their joint inversion resulted in good detectability of the lava tubes with a large size with respect to the electrode spacing. The dipole-dipole array configuration provided more accurate models for lava tubes of a size in the same order of magnitude as the electrode spacing. This study showed that the main drawbacks of ERT in heterogeneous volcanic settings are linked to lava tube-related high-resistivity anomalies which appear larger and shallower and may also be laterally shifted with respect to their true location. For lava tubes with a small size with respect to the electrode spacing our synthetic data modelling results show the difficulty in distinguishing single lava tubes from in contact lava tubes, and distinguishing lava tubes in general from void-rich zones. Overall, ERT surveys were successful in detecting lava tubes, providing a good definition of the main boundaries between different volcanic units and highlighting the presence of close, near-parallel unexplored lava tubes.
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.
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.
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.
Some of the most appealing science targets for future exploration missions in our solar system lie in terrains that are inaccessible to state-of-the-art rover technology. This paper discusses the challenges and constraints of designing a robotic explorer for these “extreme'' terrains and then examines the trade-offs among different mobility architectures. To address many of these challenges, we have developed the Axel family of rovers. The Axel rover is a two-wheeled tethered robot capable of rappelling down steep slopes and traversing rocky terrain. The DuAxel rover, which is a four-wheeled vehicle formed from two Axel rovers, provides untethered mobility to get to extreme terrains. We describe the basic design principles of these rovers and review our efforts to implement the key features of the Axel concept. Limitations found during experiments with prior Axel rover prototypes led to the design of a third-generation Axel rover. We describe the features of this new rover and then present a thermal analysis conducted to assess the feasibility of exploring lunar cold traps, which are expected to have a temperature range of 40 to 70 K. We conclude the paper with results showcasing Axel and DuAxel's extreme-terrain performance as evaluated during two recent field tests in a steeply sloped Southern California rock quarry and at a location in Arizona that closely resembles rugged Martian terrain. We also summarize lessons learned during the Axel development program. © 2012 Wiley Periodicals, Inc.
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.
- F Sauro
Sauro, F. et al. Earth-Sci. Rev. 103288 (2020).
- M J Malaska
Malaska, M. J. Icarus 344, 113764 (2020).
- L Chappaz
Chappaz, L. et al. Geophys. Res. Lett. 44, 105-112 (2017).
- P Torrese
Torrese, P. et al. Icarus 357, 114244 (2021).
- S Dubowsky
Dubowsky, S. et al. AIP Conf. Proc. 746, 1449 (2005).
- I A D Nesnas
Nesnas, I. A. D. et al. J. Field Robot. 29, 663-685 (2012).
- G E J Cushing
Cushing, G. E. J. Cave Karst Stud. 74, 33-47 (2012).
Mars Global Cave Candidate Catalog (NASA, PDS
- G E Cushing
Cushing, G. E. Mars Global Cave Candidate Catalog (NASA, PDS,
2016);