Article

Lava tubes on Earth, Moon and Mars: A review on their size and morphology revealed by comparative planetology

Authors:
  • Miles Beyond for ESA
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Abstract

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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... Various holes/skylights are especially common above lava tubes and often used in exploration for them. They are called "pukas" in Hawai'i or "jameos" in the Canary archipelagos and usually form sinuous chains (Sauro et al., 2020). Skylights usually result from collapse of the roof, which can be due to gravitational effects or flow overpressure (e.g., Cushing et al., 2015;Sauro et al., 2020) or through incomplete crusting over a lava channel developing into a lava tube. ...
... They are called "pukas" in Hawai'i or "jameos" in the Canary archipelagos and usually form sinuous chains (Sauro et al., 2020). Skylights usually result from collapse of the roof, which can be due to gravitational effects or flow overpressure (e.g., Cushing et al., 2015;Sauro et al., 2020) or through incomplete crusting over a lava channel developing into a lava tube. Kempe (2012a) distinguished two types of collapse forms: 1) a "hot puka", when the lava flow is still active and the rubble is carried away; and 2) a "cold puka", formed after the flow terminated and breakdown remains. ...
... The first, genetic observations of actively forming lava tubes by "overcrusting" of an open channel were made by Peterson and Swanson (1974) during long-lasting effusive eruptions at the Kīlauea volcano, on the Island of Hawaii. Excellent reviews of various formation processes can be found in Kempe (2012aKempe ( , 2019 and more recently in Sauro et al. (2020). ...
... Two of the main topics to be addressed are identification of in-situ resources such as H 2 O, for fuel and oxygen production in situ [88], construction materials for habitats, REE etc. (see [5,12]) and natural shelters for settlements [22,133]. Cosmic radiation, extreme temperature excursions between night and day such as 360K to 220K at the Apollo 11 landing site (according to the Apollo 11 technical memorandum, [72]), to extremely low temperatures such as at the lunar south polar regions [29] and not exceeding 100K such in the shaded areas of the Shackelton Crater [74], micrometeorites impacts and sharp, fine-grained regolith represent significant challenges for robotic system design and performance as well as life-support systems. ...
... The discovery in 2009 of the Marius Hills skylight with SELENE-Kaguya Terrain Camera [67] opened new questions on the existence [79], formation processes [33,83,133], size and stability [22,133,149] of underground voids related to drained lava tubes. The existence and entity of such voids has been inferred to be up to hundreds of meters in height by radar sounder measurements at several locations, including Marius Hills [79], gravity mass deficits with GRAIL [36] and comparative planetology with morphometric analysis of Earth analogues [133]. ...
... The discovery in 2009 of the Marius Hills skylight with SELENE-Kaguya Terrain Camera [67] opened new questions on the existence [79], formation processes [33,83,133], size and stability [22,133,149] of underground voids related to drained lava tubes. The existence and entity of such voids has been inferred to be up to hundreds of meters in height by radar sounder measurements at several locations, including Marius Hills [79], gravity mass deficits with GRAIL [36] and comparative planetology with morphometric analysis of Earth analogues [133]. ...
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The DAEDALUS mission concept aims at exploring and characterising the entrance and initial part of Lunar lava tubes within a compact, tightly integrated spherical robotic device, with a complementary payload set and autonomous capabilities. The mission concept addresses specif- ically the identification and characterisation of potential resources for future ESA exploration, the local environment of the subsurface and its geologic and compositional structure. A sphere is ideally suited to protect sensors and scientific equipment in rough, uneven en- vironments. It will house laser scanners, cameras and ancillary payloads. The sphere will be lowered into the skylight and will explore the entrance shaft, associated caverns and conduits. Lidar (light detection and ranging) systems produce 3D models with high spatial accuracy inde- pendent of lighting conditions and visible features. Hence this will be the primary exploration toolset within the sphere. The additional payload that can be accommodated in the robotic sphere consists of camera systems with panoramic lenses and scanners such as multi-wavelength or single-photon scanners. A moving mass will trigger movements. The tether for lowering the sphere will be used for data communication and powering the equipment during the descending phase. Furthermore, the connector tether-sphere will host a WIFI access point, such that data of the conduit can be transferred to the surface relay station. During the exploration phase, the robot will be disconnected from the cable, and will use wireless communication. Emergency autonomy software will ensure that in case of loss of communication, the robot will continue the nominal mission.
... On the Moon the presence of intact lava tubes has been confirmed using the SELENE Lunar Radar Sounder on Marius Hills (Kaku et al., 2017), in areas where GRAIL gravimetric measurements also suggested the presence of large underground voids . See the review paper by Sauro et al. (2020) for a recent overview on Martian and Lunar lava tubes. ...
... Similar studies might also be carried out on terrestrial volcanic terrains for the mapping of skylights and collapses of lava tubes and other volcanic caves in arid, vegetation-free areas (e.g., the large basaltic shields in Saudi Arabia, Pint, 2006). However, lava tube entrances are often very large (several meters in diameter) (Sauro et al., 2020), and are generally collapses of cave roofs, easy to spot even on low resolution satellite images and where vegetation is abundant. Given these large surface collapses typical of lava tubes, it is expected that the results will be even more accurate than those illustrated for the salt caves in the CDS. ...
... 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.
... Quasi-circular topographic depressions are observed on the surface of Earth and many planetary bodies and asteroids (e.g., Figs 1A and B) (e.g., Abelson et al., 2003;Frumkin & Naor, 2019;Horstman & Melosh, 1989;Kling et al., 2021;Martin et al., 2017;Okubo & Martel, 1998;Sauro et al., 2020;Scott & Wilson, 2002;Whitten & Martin, 2019;. These depressions, termed 'pit craters', have diameters of meters to thousands of meters and commonly arranged in linear chains (e.g., Kling et al., 2021;Whitten & Martin, 2019). ...
... The lack of raised rims and ejecta deposits around pit craters suggest they are not formed by meteorite impacts (e.g., Figs 1A and B) (e.g., Halliday, 1998;Poppe et al., 2015;. Instead, pit craters are thought to reflect collapse of overlying rock and/or regolith into subsurface cavities or volumetrically depleted zones generated by ( Fig. 1C) (see also : (i) the dissolution of carbonate or salt (e.g., sinkholes; Abelson et al., 2003;Poppe et al., 2015;Spencer & Fanale, 1990); (ii) local porosity reduction of the host material following hydrothermal fluid flow or fault-related overpressure release (e.g., pockmarks; Velayatham et al., 2019;Velayatham et al., 2018); (iii) evacuation of lava tubes (see Sauro et al., 2020 and references therein); (iv) opening of tensile fractures (e.g., Smart et al., 2011;Tanaka & Golombek, 1989); (v) local dilation where faults are steeply dipping (e.g., Ferrill & Morris, 2003;Ketterman et al., 2015;Smart et al., 2011;; (vi) dyke intrusion (e.g., Mège & Masson, 1996;Okubo & Martel, 1998;Scott & Wilson, 2002;Wall et al., 2010); (vii) magma migration out of a reservoir (e.g., Mège et al., 2003;Poppe et al., 2015); and/or (viii) explosive volcanism (e.g., Hughes et al., 2018). . (Kling et al., 2021). ...
... Basemap is THEMIS Daytime-IR. (C) Conceptual models of pit crater formation (modified from Kettermann et al., 2019;Sauro et al., 2020;Velayatham et al., 2019;Velayatham et al., 2018;. ...
... The conduit can be drained at the end of the eruption becoming an accessible linear void following the slope of the volcanic edifice. Lava tubes can be either a single conduit with rectilinear or rather sinuous path, or braided conduits presenting different superposed levels at depth (Sauro et al., 2019(Sauro et al., , 2020Kempe, 2012;Kempe et al., 2010). Such conduits usually form during effusive eruptions in presence of very hot and fluid basaltic lava and gentle slopes. ...
... Different genetic mechanisms have been described, depending on the lava rheology, slope and effusion rates (Sauro et al., 2020). The "overcrusting" formation mechanism occurs when such fluid lavas channelize and the open surface of the lava channel cools down faster due to the high delta of temperature with the atmosphere. ...
... The cooling process of the underlying -still active-lava channel is inhibited by the thermal insulation of the newly formed roof and allows lava to continue to flow until the eruption stops or the effusion rate decreases. The size of such conduits is relatively small on Earth, (1-10 m of width) although they can reach impressive lengths such as Kazumura cave in Hawaii (see details in Sauro et al., 2020). A second genetic mechanism which is less common on Earth but seems to be more prominent on Mars and the Moon is the "inflation" process. ...
Article
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.
... The conduit can be drained at the end of the eruption becoming an accessible linear void following the slope of the volcanic edifice. Lava tubes can be either a single conduit with linear, sinuous, or braided paths at different superposed depths (Sauro et al., 2019(Sauro et al., , 2020Kempe, 2012;Kempe et al., 2010). Such conduits usually form during effusive eruptions in the presence of hot, fluid basaltic lava and relatively gentle slope gradients. ...
... Different mechanisms for the generation of these lava tubes have been described based on rheology, slope and effusion rates (Sauro et al., 2020). The "overcrusting" or encrusting mechanisms occur when such fluid lava is channelized and the surface of the lava channel cools quickly due to the contact with the cooler atmosphere. ...
... The size of such conduits is relatively small on Earth, (1-10 m in width) although they can reach impressive widths such as the Kazumura cave in Hawaii (see details in Sauro et al., 2020). A second genetic mechanism that is less common on Earth but seems to be more prominent on Mars and the Moon is the "inflation" process. ...
Article
The paper presents new results from microseismic data analysis for the detection and delineation of near-surface lava tubes. Single-station, free-field seismic noise data were collected at the Corona Volcano area (Lanzarote, Canary Islands) as part of the PANGAEA-X 2017 European Space Agency (ESA) astronaut training campaign. The site was selected as it represents a suitable analogue for lunar maria and provided the opportunity to cross-validate and ground truth seismic and other geophysical studies. In this paper, we present our observations on the distribution of frequencies and amplitudes of standing waves generated by microtremors in the space between the ground surface and underground cavities by averaging amplitude spectra of microseismic records. This study shows that the frequency of the vertical component peaks is a relatively good indicator of presence, lateral extent and approximate dip of the cavities. However, only the vertical component peaks with a frequency either equal to or close to central to high amplitude (3.1–8.5) horizontal-to-vertical (H/V) peaks are related to lava tubes. If the P-wave velocities in the rocks overlying the lava tubes are known, then these frequencies can also be used to estimate the depth of such cavities. This study also identified some important pitfalls that may limit the use and accuracy of our approach. These include layering of rocks overlying the lava tubes, lateral changes in thickness, lateral variations of the P-wave velocity, and the presence of shallow void-rich zones. Overall, the results of this study confirmed that microseismic data are suitable for cavity detection. It is also, to our knowledge, one of the first studies dealing with microseismic data from near-surface lava tubes. With the recent increase in planetary exploration, this method can be easily adapted to support the geophysical exploration of volcanic terrains on the Moon and Mars.
... Lava tubes form when a flow of lower viscosity lava, typically mafic in composition, develops a solidified surface while maintaining an interior of flowing fluid lava. The formation mechanisms by which the surface solidification of the molten lava can occur in general includes the solidification of the crust of a inflating pahoehoe lava flow or the roofing over of an established lava flow channel, but in all cases this hardened surface provides an insulating layer for the molten lava that continues to flow underneath (Greeley, 1972;Hon et al., 1994;Peterson & Swanson, 1974a;Sauro et al., 2020). In the cases where the roof becomes structurally capable of supporting itself, and the molten lava drains from the enclosed interior, a hollow lava tube, or cave, is left behind within the solidified lava flow. ...
... In the case of lava tube formation from an inflating lava flow, the flow front will consist of a series of overlapping lobes of lava that fuse and cool to form the roof of the lava tube (Greeley, 1971b;Peterson et al., 1994;Sauro et al., 2020). This mechanism generally occurs in slow moving lava flows and result in irregular constructs in comparison to tubes forming from continuous surface crusts (Greeley, 1971b). ...
... Lava tubes originating from channel flows can be the result of several formation mechanisms. One possibility is for the crust to solidify along the channel edges via cooling and then grow toward the centerline of the channel, progressing downstream in a V-shape, essentially zippering over the channel (Greeley, 1971b;Peterson et al., 1994;Sauro et al., 2020). Another possibility, in channels with stable flow, is for the flow surface to develop a scum or crust. ...
Article
Full-text available
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.
... In the last two decades, various satellite missions have confirmed the presence on the Moon of peculiar pits that could allow access to subsurface voids ( [1], [2]). This discovery has led notable scientific debate on the geological nature of these cavities and on what may be found in their interior ( [3]). Since the early seventies several authors ( [4], [5], [6]) have argued that J o u r n a l P r e -p r o o f Journal Pre-proof which each layer of cooled lava is lifted by the following lava wave, leading to even larger, more complex cavities [8]. ...
... Lava tubes on Earth are common in basaltic shield volcanoes and, by analogy, they are also expected to be common in lunar Maria. In [3], it is shown that differences in planetary parameters (gravity, thickness of the crust, effusion rates, surface temperatures, etc.) could lead to the formation of lunar tubes that could reach hundreds of meters in diameter, be several kilometers long, with volumes of hundreds of millions of cubic meters. Access to lunar lava tubes might be found in some lunar pits, when they represent proper skylights, areas in which the ceiling of a tube has collapsed ( [9]). ...
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.
... Caves develop mainly in karstic areas, where infiltrating water dissolves soluble rocks such as limestone, dolostone, gypsum, to create extensive networks of voids underground [9]. However, caves can also be found in volcanic areas (lava tubes and evacuated magma chambers) [10], in extremely resistant lithologies such as quartzites [11], in salt deserts [12] and inside glaciers (ice caves due to melt [13]). Although caves can be found in a wide range of environments, they share some general characteristics, such as complete darkness. ...
... In addition to the human behaviour and performance benefits that the CAVES training provides, caves on other planetary bodies (especially the Moon and Mars) could be among the main objectives for exploration and astrobiology research in the future [73,74]. Recent studies have shown that the volume of these tubes on Mars and the Moon could be up to two or three orders of magnitude larger than terrestrial analogues, respectively [10]. Intact, open segments of lava tubes could provide stable shelters for human habitats shielded by cosmic radiation and micrometeorite impacts on the Moon [75]. ...
Article
Caves remain among the most challenging exploration frontiers on planet Earth. They are difficult to access, present a range of unique and unusual environmental characteristics, and can only be mapped through direct human exploration. These challenges and several environmental factors specific to caves mean that speleology shares several analogies with space missions. For humans, cave exploration imposes isolation, confinement, minimal privacy, technical challenges, limited equipment and supplies, a sense of disconnect from the surface and regular life, a lack of diurnal cycles, and the constant presence of risk. As many of the same challenges are imposed on humans during space exploration, in 2005 the European Space Agency (ESA) began examining the possibility of using natural cave systems as a platform for astronaut training. These efforts resulted in a new ESA training programme named CAVES (Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills) being launched in 2011, involving astronauts from partner space agencies. The primary objective of this training is to enhance astronaut individual and team performance and behavioural competencies by exposing them to the challenges of a real mission into an unknown and dangerous environment. To achieve this, the course's training activities are based around a real scientific and technological programme focused on cave science. Many aspects of the location and course content have been designed by a team of behavioural experts, scientists, trainers, operations engineers and speleologists with the support of caving organizations and schools. CAVES training events leverage cave exploration to create situations that are analogues to spaceflight in terms of safety protocols, perception and management of risk, crew composition and role assignments, group living, isolation, and confinement. In addition, these courses provide an opportunity for astronauts to experience spaceflight-like or relevant operations, science, equipment testing, and exploration, in preparation for future planetary endeavours. The scientific, exploration and equipment testing aspects of the course are real (not simulated). This ensures that these activities provide benefits to the speleological and scientific communities, whilst guaranteeing the realism of these activities for training purposes. During six editions of CAVES, from 2011 to 2019, 34 astronauts from 6 different space agencies (ESA, NASA, JAXA, ROSCOSMOS, CSA and CNSA) have taken part in the training. The CAVES training programme has been recognized by all participant astronauts and, in particular, by those who have travelled to space, as one of the best space analogue training opportunities available on Earth. The learning outcomes are applicable to both current and future orbital missions, as well as surface and subsurface missions to other planetary bodies.
... The link between pit craters and dikes and faults confirms that magmatic processes and overburden collapse into dilatational fault jogs. By recognizing that some pit craters above dikes occur at different stratigraphic levels and broadly get younger southwards, we specifically suggest these pit craters may have formed when a waning of magma pressure and potential backflow led to a local volume reduction of Kettermann et al., 2019;Sauro et al., 2020;Velayatham et al., 2019;Velayatham et al., 2018;Wyrick et al., 2004). the dike. ...
... The only cross-section attributes commonly available to measure for most pit craters on Earth and other planetary bodies are their depth and slope; together, these parameters can be used to estimate pit volume (e.g., Gwinner et al., 2012;Sauro et al., 2020;Scott & Wilson, 2002;Wyrick et al., 2004). Most pit craters we study (54; i.e., 92%) display a funnel-like morphology comprising an upper, inwardly inclined conical surface, which we refer to as an "inverted cone", underlain by a sub-vertical cylindrical "pipe" (e.g., Figure 3a). ...
Article
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Pit craters are quasi‐circular depressions observed on rocky and icy planetary bodies, as well as numerous asteroids. Pit craters are thought to form by overburden collapse into a subsurface cavity or volumetrically depleted zone. Importantly, the surface size and distribution of pit craters may provide an important record of otherwise inaccessible subsurface processes. However, because we cannot access the subsurface of many planetary bodies, we rely on physical and numerical models to infer processes linked to pit crater formation. Here, we use 3D seismic reflection data to quantify the palaeosurface and subsurface geometry of 59 Late Jurassic pit craters buried to depths of ∼3 km within a sedimentary basin, offshore NW Australia. The pit craters are typically funnel‐like, with an inverted conical upper section underlain by a pipe. Pit crater depths, that is, the height of inverted cone sections, correlate with their plan‐view length, consistent with observations of pit craters elsewhere; this trend is rendered less apparent by later sediment‐infilling. For the first time, we show some pit crater pipes connect to underlying igneous dikes or steeply dipping, likely dilatational portions of normal faults. Although some pit craters seemed to have formed due to faulting and others to dyking, they cannot be differentiated based on their surface expression. Our data also suggest pit crater size may not relate to the mechanical properties of the host material. Overall, we conclude that the surface expression of pit craters on Earth and other planetary bodies may not be diagnostic of subsurface processes or properties.
... On Mars, sinuous rilles and various other volcanic channel forms, alignments of small source vents, chains of depressions, and ridged and plateau lava flow morphologies have been identified and various aspects of their morphologies discussed in comparison to terrestrial lava tubes and tube-fed lava flows, which are often subject to inflation (e.g., Bleacher et al., 2007Bleacher et al., , 2017Crown & Ramsey, 2017;Hamilton et al., 2020;Hauber et al., 2009;Keszthelyi et al., 2006;Theilig & Greeley, 1986). Recent reviews by Kempe (2019) and Sauro et al. (2020) provide detailed summaries of past research, including lava tube morphologies and processes. In particular, Sauro et al. (2020) review important terminology and concepts related to lava tube formation processes and make detailed morphometric comparisons between features on the Earth, Moon, and Mars. ...
... Recent reviews by Kempe (2019) and Sauro et al. (2020) provide detailed summaries of past research, including lava tube morphologies and processes. In particular, Sauro et al. (2020) review important terminology and concepts related to lava tube formation processes and make detailed morphometric comparisons between features on the Earth, Moon, and Mars. ...
Article
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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.
... Lava tubes are usually at shallow depths, so geothermal (or "areothermal" on Mars) heat does not play a major role. Based on orbital imagery, Cushing et al. (2007) determined minimum depths at skylight entrances of 68-130 m. Sauro et al. (2020) measured the depths of the collapses for five Martian caves in the range 16-60 m. For dense rock, the areothermal gradient may be 15 K/km. ...
... In a gas, the kinematic viscosity ν and thermal diffusivity κ are almost identical, ν ≈ κ. (Their ratio, the Prandtl number, is close to 1.) Since ν is about 50 times larger on Mars than on Earth, the Rayleigh number is much lower on Mars. Lava tubes can be larger on Mars than on Earth (Sakimoto et al., 1997;Sauro et al., 2020), but they would have to have more than ten times the diameter to have similar Rayleigh numbers. The Rayleigh number serves as a threshold condition for the onset of convection, and it depends on the geometry of the cavity. ...
Article
Caves on planet Mars could potentially contain water ice deposits. Here, the physical processes responsible for the growth and preservation of spelean ice formations on Mars are assessed. Martian caves are situated in environments where phase transitions of water are only by sublimation. The predominant type of cave ice is expected to be perennial hoarfrost that slowly grows in supersaturated cavities. The role of cave microclimates for maintaining ice bodies is evaluated comparatively. Free and forced convection transport less sensible heat than in the denser terrestrial atmosphere. Cooling through sublimation is also expected to be far weaker in Martian caves than in terrestrial caves. Hence, the cooling of ice deposits by flow through the cave, often a crucial factor in terrestrial ice caves, is insignificant on Mars, which limits the geographic extent where cave ice deposits can be expected.
... We reproduced experimentally at lab scale the alteration of a fresh alkaline basaltic rock collected at Etna Mount. We selected Etna Mount as a Martian analogue for the following reasons: (i) the basalts are compositionally similar to those identified in different areas of the Martian surface [41]; (ii) the volcanic morphologies such as basaltic channels, caves and lava tubes are widely exposed on the Etna active volcano and are very similar to those observed on Mars [42,43]. ...
... In particular, the formation of smectite which preserves a microbial signature is well observed in hydrothermal systems of hot springs [76,90]. Caves and lava tubes represent other environments where the preservation of microbial biosignatures, or traces of life, in mineral deposits also occur [43]. ...
Article
Full-text available
Clay minerals have been detected on Mars to outcrop mainly as alteration of ancient bedrock, and secondarily, as deposition from aqueous environments or interlayered with evaporitic deposits on Mars. In order to better constrain the alteration environments, we focused on the process to form clays from volcanic rocks and experimentally reproduced it at different temperature and pH. A fresh, holocrystalline alkali‐basalt sample collected in the Mount Etna volcanic sequence has been used as analogue of the Martian unaltered bedrock. Previous works considered only volcanic glass or single mineral, but this may not reflect the full environmental conditions. Instead, we altered the bulk rock and analyzed the changes of primary minerals to constrain the minimum environmental parameters to form clays. We observed that under acidic aqueous solution (pH ~ 3.5– 5.0) and moderate temperature (~150–175 °C), clinopyroxene and plagioclase are altered in smectite in just a few days, while higher temperature appear to favor oxides formation regardless of pH. Plagioclases can also be transformed in zeolite, commonly found in association with clays on Mars.This transformation may occur even at very shallow depth if a magmatic source is close orhydrothermalism is triggered by meteoritic impact.
... In particular, Hawaiian lava tubes are of interest to astrobiology studies and upcoming missions to Mars (Boston et al., 2001;Northup et al., 2011;Bauermeister et al., 2014;Tarnas et al., 2021). Volcanic systems in Hawai'i are geologically like those on ancient Mars, which had active volcanoes and fumaroles (Farmer, 1996;Thollot et al., 2012;Hynek et al., 2018;Sauro et al., 2020). High-resolution satellite images from various orbital spacecraft show that Martian volcanoes were built from countless individual flows, many of which were created through channels and lava tubes, signaling a style of volcanism analogous to Hawaiian eruptions (Sauro et al., 2020). ...
... Volcanic systems in Hawai'i are geologically like those on ancient Mars, which had active volcanoes and fumaroles (Farmer, 1996;Thollot et al., 2012;Hynek et al., 2018;Sauro et al., 2020). High-resolution satellite images from various orbital spacecraft show that Martian volcanoes were built from countless individual flows, many of which were created through channels and lava tubes, signaling a style of volcanism analogous to Hawaiian eruptions (Sauro et al., 2020). With these geological similarities, Hawaiian volcanic environments can provide some insight into the possibility of life on Mars in its ancient past and how microbial communities could survive today on Mars in lava caves, or if introduced from Earth (forward contamination). ...
Article
Full-text available
Lava caves, tubes, and fumaroles in Hawai'i present a range of volcanic, oligotrophic environments from different lava flows and host unexpectedly high levels of bacterial diversity. These features provide an opportunity to study the ecological drivers that structure bacterial community diversity and assemblies in volcanic ecosystems and compare the older, more stable environments of lava tubes, to the more variable and extreme conditions of younger, geothermally active caves and fumaroles. Using 16S rRNA amplicon-based sequencing methods, we investigated the phylogenetic distinctness and diversity and identified microbial interactions and consortia through co-occurrence networks in 70 samples from lava tubes, geothermal lava caves, and fumaroles on the island of Hawai'i. Our data illustrate that lava caves and geothermal sites harbor unique microbial communities, with very little overlap between caves or sites. We also found that older lava tubes (500-800 yrs old) hosted greater phylogenetic diversity (Faith's PD) than sites that were either geothermally active or younger (<400 yrs old). Geothermally active sites had a greater number of interactions and complexity than lava tubes. Average phylogenetic distinctness, a measure of the phylogenetic relatedness of a community, was higher than would be expected if communities were structured at random. This suggests that bacterial communities of Hawaiian volcanic environments are phylogenetically over-dispersed and that competitive exclusion is the main driver in structuring these communities. This was supported by network analyses that found that taxa (Class level) co-occurred with more distantly related organisms than close relatives, particularly in geothermal sites. Network "hubs" (taxa of potentially higher ecological importance) were not the most abundant taxa in either geothermal sites or lava tubes and were identified as unknown families or genera of the phyla, Chloroflexi and Acidobacteria. Prescott et al. Islands Within Islands These results highlight the need for further study on the ecological role of microbes in caves through targeted culturing methods, metagenomics, and long-read sequence technologies.
... Nevertheless, when trying to build a habitat in an off-Earth environment like Mars, much of the heavy machinery and tools are unavailable, due to the limited payload of the spaceship. Furthermore, if the habitat is built inside a cave to offer protection from solar radiation [1], the construction process is also confined to smaller places, where machinery would not fit. Hence, the construction process has to be adjusted to these limitations. ...
... The Rhizome project of the European Space Agency plans to build a human habitat in existing lava caves on Mars [1]. The aim of the project is to build these living structures out of 3D-printed concrete voronoi building modules [2]. ...
Poster
Full-text available
Space exploration is characterized by a limited amount of resources and tools. This particularly stands out in habitat construction, where heavy machinery like cranes are unavailable and manual work still plays a key role. To mitigate this, we propose a human-robot collaboration method for habitat construction tasks, which involve several key sub-tasks: grasping objects of various shapes, carrying them, and aligning them for assembly. The proposed method is based on an impedance controller and includes four modes of operation, that are tailored for specific sub-tasks. Each mode prescribes a robot stiffness behavior, needed for collaborative execution. The human operator can easily switch between the mode in real-time via a voice interface. To demonstrate the functionality of the proposed method in the construction task, we performed an experiment using KUKA LBR iiwa robot arm and qb robotics SoftHand robotic hand. These results indicate that the method offers a practical solution for human-robot collaborative construction tasks.
... Another potentially interesting but technologically challenging deployment location are lava tubes (Sauro et al. 2020;Theinat et al. 2020), where temperatures are expected to be more stable around the average ground temperature of 250 K (Horvath & Hayne 2018). ...
Article
Full-text available
Monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. At laboratory scale, these experiments became known as resonant bar detectors first developed by Joseph Weber in the 1960s. Due to the dimensions of these bars, the targeted signal frequencies were in the kHz range. Weber also pointed out that monitoring of vibrations of Earth or the Moon could reveal gravitational waves in the mHz band. His Lunar Surface Gravimeter experiment deployed on the Moon by the Apollo 17 crew had a technical failure, which greatly reduced the science scope of the experiment. In this article, we revisit the idea and propose a Lunar Gravitational-Wave Antenna (LGWA). We find that LGWA could become an important partner observatory for joint observations with the space-borne, laser-interferometric detector LISA and at the same time contribute an independent science case due to LGWA's unique features. Technical challenges need to be overcome for the deployment of the experiment, and development of inertial vibration sensor technology lays out a future path for this exciting detector concept. © 2021. The Author(s). Published by the American Astronomical Society.
... Frequently, however, the more relevant parameter is the existence and the depth of an interfacing boundary, such as the bottom of Europa's ice shell (e.g., Nimmo et al., 2003Nimmo et al., , 2007, the thickness of buried ice sheets on Mars (e.g., Bramson et al., 2015;Stuurman et al., 2016), the location of ice-rich materials on the Moon and/or Mercury (e.g., Rubanenko et al., 2019), or the ceiling and floor of lunar and Martian caves/lava tubes (e.g., Kaku et al., 2017;Chappaz et al., 2017;Sauro et al., 2020;Sood et al., 2016aSood et al., , 2016b. The case in Figure 1 has clearly demonstrated that, although noise dominates the measurement below 3.5 km, a boundary at 4.7 km can still be detected. ...
Article
Full-text available
We modified and justified the radar equation for ground penetration by including the backscattering effect. We propose a strawman system on an orbiter 50 km above the surface based on lunar conditions. The Tightly coupled dipole arrays antenna substantially reduces the size and mass and consists of an array with 8 × 8 cells on a light weight plate that is 1.6²‐m² wide with cells 0.25‐m high providing increased directionality and beam‐steering capability. The system includes 8 transmitters and 16 receivers that are able to measure wave polarization so that it is sensitive to subsurface water/ice. The system is controlled by central computers with transceivers all programmable providing more functionalities and flexibilities enabling systems of an even larger number of transceivers. It uses the synthetic aperture radar method to enhance the spatial resolution along the orbit track and has phase steering capability to increase the resolution in the cross‐track direction. The total transmitted power is 160 W. The radar is able to operate in three modes: a fine‐resolution mode that provides the full Multiple‐Input Multiple‐Output ultrawideband (MIMO UWB) capability with vertical range resolution up to 0.2 m, a deep penetration mode that is able to penetrate 100 m for high attenuation targets or over few kilometers for low attenuation targets, and a survey mode that provides overall characterization of the planet economically. This system can provide internal properties and structures of a target and detailed information about most useful resources such as ice, water, minerals, and shelter caves, for human space exploration on the Moon, Mars, and asteroids.
... These caves have been studied by remote sensing and have not been explored by dedicated missions, although some were proposed and developed, such as Moon Diver [53] and rock climber Lemur [54]. Lava tubes have been morphologically related to ones formed on Earth in volcanic rock by a volcanic eruption [55]. SISPO could be utilised for synthesising versatile sets of lava-caves images for (i) developing navigation algorithms and sampling spots detection by image processing (e.g., biological mats or their preserved remains on the geological substrate) or (ii) mapping the caves by photogrammetry for potential human settlements. ...
Preprint
Full-text available
This paper describes the architecture and demonstrates the capabilities of a newly developed, physically-based imaging simulator environment called SISPO, developed for small solar system body fly-by and terrestrial planet surface mission simulations. The image simulator utilises the open-source 3D visualisation system Blender and its Cycles rendering engine, which supports physically based rendering capabilities and procedural micropolygon displacement texture generation. The simulator concentrates on realistic surface rendering and has supplementary models to produce realistic dust- and gas-environment optical models for comets and active asteroids. The framework also includes tools to simulate the most common image aberrations, such as tangential and sagittal astigmatism, internal and external comatic aberration, and simple geometric distortions. The model framework's primary objective is to support small-body space mission design by allowing better simulations for characterisation of imaging instrument performance, assisting mission planning, and developing computer-vision algorithms. SISPO allows the simulation of trajectories, light parameters and camera's intrinsic parameters.
... These underground conduits have their surface expression in sinuous alignments of rimless collapse pits elongated in the direction of the underground conduit path. Some of these collapses are very large and extend for the maximum width of the tube (Sauro et al., 2020), whereas skylights are smaller in dimension, circular or sub-circular with overhanging walls, therefore hinting for the presence of a larger underground void below. Skylighs have been described and systematically detected by Cushing et al., (2015) and a comprehensive Mars-wide database is now available and maintained from USGS called Mars Global Cave Candidate Catalog (Cushing and Okubo, 2015). ...
Article
Full-text available
The objective of this document is the definition of a set of cartographic and technical standards and directions to be used, adapted or -in minor form -established for GMAP. Standards proposed and mentioned in the present documents include geologic and cartographic aspects. Some of the proposed directions and standards are initial ones that are planned to be refined and/or updated throughout the Europlanet H2024RI project, to be used within the VA activities and for future sustainable European planetarymapping efforts beyond the RI.The state of the art and relevant documents are included, as well as process-specific and body-specific best practice and exemplary published cases. The approaches for two-dimensional mapping and three-dimensional geologic mapping and modelling are introduced, as well as the range of non-standard map types that are envisaged within GMAP activities. Mapping review directions are indicated, as well data sharing, distribution and discovery.Proposed standards, best practice, andtools are based on existing ones or on additional or new developments and adaptations.Appendices are included and point to either individual developments or external resources and tools that will be maintained throughout the duration of the research infrastructure, and beyond it, through sustainability.The present document is going to be a live document permanently accessible on the GMAP wiki and periodically updated in form of a deliverable.
... Pit chains have been considered as the result of dilational normal faulting (Ferrill et al., 2011;Wyrick et al., 2004), karst dissolution (Spencer & Fanale, 1990), extensional fractures (Tanaka & Golombek, 1989), collapsed buried conduits, particularly in the cases of sinuous patterns (Sauro et al., 2020), events of explosive activity due to magma-water interactions (Head & Wilson, 2007), and dyke intrusions (Cushing et al., 2015;Mège & Masson, 1996;Mége et al., 2000;Montési, 2001;Pozzobon et al., 2015;Scott & Wilson, 2002;Wilson & Head, 2002). ...
Article
Full-text available
Chaotic terrains are broad regions on Mars characterized by the disruption of the basaltic bedrock into polygonal blocks separated by deep fractures. To date, the proposed genetic scenarios often involve the occurrence of subsurface ice or liquid H2O. Nevertheless, similar features also occur within some craters on the Moon, namely floor-fractured craters (FFCs), where water ice reservoirs are not present. We propose a new formation mechanism for Martian chaotic terrains as well as for lunar and Martian FFCs. The proposed mechanism does not require a major role of water but multiple cycles of inflation and deflation of a buried magma chamber. This process results in a particular type of caldera collapse, called the piecemeal (or chaotic) caldera collapse. A series of analogue experiments show both geometrical and quantitative correspondence with natural case studies: Arsinoes Chaos (Mars), an unnamed FFC (Mars), Komarov crater (FFC on the Moon).
... The origin of such craters is somewhat contentious (see [4,7,8]). However, their morphology and geometric relations have led many authors to conclude that they are the surface traces of open voids or fractures in an underlying body due to a variety of possible formation mechanisms: extensional fracturing and dilational faulting, karstic dissolution, thermokarst processes related to sublimation or melt of ground ice, shallow dike intrusion, and lava tube collapse (e.g., [5,8,[13][14][15][16][17][18]). ...
Article
Full-text available
Pit craters are now recognised as being an important part of the surface morphology and structure of many planetary bodies, and are particularly remarkable on Mars. They are thought to arise from the drainage or collapse of a relatively weak surficial material into an open (or widening) void in a much stronger material below. These craters have a very distinctive expression, often presenting funnel-, cone-, or bowl-shaped geometries. Analogue models of pit crater formation produce pits that typically have steep, nearly conical cross sections, but only show the surface expression of their initiation and evolution. Numerical modelling studies of pit crater formation are limited and have produced some interesting, but nonetheless puzzling, results. Presented here is a high-resolution, 2D discrete element model of weak cover (regolith) collapse into either a static or a widening underlying void. Frictional and frictional-cohesive discrete elements are used to represent a range of probable cover rheologies. Under Martian gravitational conditions, frictional-cohesive and frictional materials both produce cone- and bowl-shaped pit craters. For a given cover thickness, the specific crater shape depends on the amount of underlying void space created for drainage. When the void space is small relative to the cover thickness, craters have bowl-shaped geometries. In contrast, when the void space is large relative to the cover thickness, craters have cone-shaped geometries with essentially planar (nearing the angle of repose) slope profiles. Frictional-cohesive materials exhibit more distinct rims than simple frictional materials and, thus, may reveal some stratigraphic layering on the pit crater walls. In an extreme case, when drainage from the overlying cover is insufficient to fill an underlying void, skylights into the deeper structure are created. This study demonstrated that pit crater walls can exhibit both angle of repose slopes and stable, gentler, collapse slopes. In addition, the simulations highlighted that pit crater depth only provides a very approximate estimate of regolith thickness. Cone-shaped pit craters gave a reasonable estimate (proxy) of regolith thickness, whereas bowl-shaped pit craters provided only a minimum estimate. Finally, it appears that fresh craters with distinct, sharp rims like those seen on Mars are only formed when the regolith had some cohesive strength. Such a weakly cohesive regolith also produced open fissures, cliffs, and faults, and exposed regolith “stratigraphy” in the uppermost part of the crater walls.
... In particular, the formation of smectite which preserves a microbial signature is well observed in hydrothermal systems of hot springs [76,90]. Caves and lava tubes represent other environments where the preservation of microbial biosignatures, or traces of life, in mineral deposits also occur [43]. ...
Article
Full-text available
Clay minerals have been detected on Mars to outcrop mainly as alteration of ancient bedrock, and secondarily, as deposition from aqueous environments or interlayered with evaporitic deposits on Mars. In order to better constrain the alteration environments, we focused on the process to form clays from volcanic rocks and experimentally reproduced it at different temperature and pH. A fresh, holocrystalline alkali-basalt sample collected in the Mount Etna volcanic sequence has been used as analogue of the Martian unaltered bedrock. Previous works considered only volcanic glass or single mineral, but this may not reflect the full environmental conditions. Instead, we altered the bulk rock and analyzed the changes of primary minerals to constrain the minimum environmental parameters to form clays. We observed that under acidic aqueous solution (pH ~ 3.5-5.0) and moderate temperature (~150-175 °C), clinopyroxene and plagioclase are altered in smectite in just a few days, while higher temperature appear to favor oxides formation regardless of pH. Plagioclases can also be transformed in zeolite, commonly found in association with clays on Mars. This transformation may occur even at very shallow depth if a magmatic source is close or hydrothermalism is triggered by meteoritic impact.
... Furthermore, the surface particle flux directionality is also different from the original, incoming isotropic GCR flux . On Mars, one idea that has been prominently discussed is to locate bases in lava tubes, which can provide significant radiation shelter (Sauro et al., 2020). Further options of interest are smaller natural features such as rock walls, overhangs, or stable caves. ...
Article
Full-text available
Protecting astronauts from the effects of space radiation remains one major stepping stone for the exploration of Mars. Long‐term exposure to radiation can lead to severe health effects and affects allowable mission duration. Mission designs for Mars include the use of radiation shelters that provide additional mass to surround the astronauts. This leads to incoming radiation losing energy through ionization processes. This is important during solar energetic particle events when solar protons can reach the surface with high intensities. Additionally, shelters provide a long‐term reduction of the exposure to galactic cosmic rays. As mass is an important time and cost factor in space travel, using natural sheltering already on Mars is a desirable option. One candidate is to use subterranean lava tubes that provide shelter from the radiation from above. Other options include craters, cliff walls, or rock overhangs. Here, we present the first in situ measurements of radiation sheltering by natural environments on the surface of Mars. The data were acquired with the Radiation Assessment Detector (RAD) on board the Curiosity rover in Gale crater on Mars. We show measurements from when Curiosity was parked close to Butte M12 in the Murray Buttes formation, which blocked out 19% of the surrounding sky view. During this time, from Mars Science Laboratory (MSL) sol 1456–1467, we find a decrease of 4% in the expected dose rate, and a decrease of 7.5% in the neutral particle environment. This proof of principle is an important step to validate plans to use natural sheltering on Mars.
... The stability of the underground is so even to cosmic radiation, making old mines as unique windows into quantum mechanics (Wolfendale 1968;Curceanu et al. 2017). For the very same reason, lava tubes are projected to host our first Martian and Lunar colonies (Sauro et al. 2020), whereas, in the domain of exobiology, cave microbiological studies are expected to bring important clues on the origin of extraterrestrial life (Northup et al. 2011;Popa et al. 2011). Not to mention, coming back on Earth, the role that cave organisms can play in the realm of medicine (Riddle et al. 2018;Yoshizawa et al. 2018) and pharmaceutics (Cheeptham et al. 2013;Ghosh et al. 2017;Genilloud 2018). ...
Article
Full-text available
Whereas scientists interested in subterranean life typically insist that their research is exciting, adventurous, and important to answer general questions, this enthusiasm and potential often fade when the results are translated into scientific publications. This is because cave research is often written by cave scientists for cave scientists; thus, it rarely “leaves the cave”. However, the status quo is changing rapidly. We analysed 21,486 articles focused on subterranean ecosystems published over the last three decades and observed a recent, near-exponential increase in their annual citations and impact factor. Cave research is now more often published in non-specialized journals, thanks to a number of authors who are exploiting subterranean habitats as model systems for addressing important scientific questions. Encouraged by this positive trend, we here propose a few personal ideas for improving the generality of subterranean literature, including tips for framing broadly scoped research and making it accessible to a general audience, even when published in cave-specialized journals. Hopefully, this small contribution will succeed in condensing and broadcasting even further the collective effort taken by the subterranean biology community to bring their research “outside the cave”.
... 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. Cave roof thickness also has a significant impact on the air temperature in the cave, resulting in negligible influence of the surface temperature on the environment inside the cave. ...
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.
... Subterranean adapted fauna importantly contributes to the pool of endemic species in many archipelagos (Naranjo et al. 2020). Lava tubes are the most iconic example amongst their caves (Sauro et al. 2020). However, caves are just a small, human-accessible fraction of the subterranean habitats available to potential colonisers. ...
Preprint
Full-text available
Using subterranean fauna in the Canary Islands as a simplified natural laboratory, we explored how the interplay of eco-evolutionary processes shape taxonomic and functional diversity patterns in oceanic archipelagos through geological times. First, we demonstrated an overall convergence in the trait spaces of subterranean communities across islands, yet with variability according to each island's ontogenetic state young, mature, or senescent. Next, we showed that the reduced species contribution to the island's traits space in mature islands is a consequence of an optimisation of the use of the available niche space driven by species interactions. Finally, we link those lines of evidence showing that species interactions select a non-random combination of traits in mature islands. Collectively, our results provided a mechanistic description of the drivers of diversity in oceanic islands by suggesting causal relationships between species functional properties and island diversity metrics accounting for their geological age. Towards a mechanistic explanation of Island biogeography using subterranean animal communities Running title: Towards a mechanistic explanation of island biogeography
... constituyen verdaderas cuevas, a veces de dimensiones internas notables, pero casi siempre situados a poca profundidad, dada su particular génesis a partir de flujos de lava superficiales (Socorro & Oromí, 2018). En cualquier caso, ciertos tubos de lava también pueden formarse por inflamiento de terrenos volcánicos relativamente profundos (Sauro et al., 2020), o incluso, los tubos volcánicos muy antiguos pueden haber sido cubiertos sucesivamente por una o varias erupciones posteriores, quedando situados en un medio subterráneo profundo, como la Cueva de Aslobas en Gran Canaria (Fernández et al., 2015). ...
Article
Full-text available
RESUMEN Se relacionan los diferentes tipos de medios subterráneos habitables existentes en los terrenos volcánicos, con especial énfasis en los distintos tipos de redes de mesocavernas (medio subterráneo superficial, depósitos de piroclastos) y de macrocavernas (tubos volcánicos, simas y diques vaciados). Se presenta una tabla de riqueza de cuevas en las islas de la Macaronesia, y se analizan las particularidades ambientales de las cuevas volcánicas. Se comentan los tipos de adaptaciones de la fauna subterránea y se aportan datos de diversidad de dicha fauna en Canarias, con comentarios taxonómicos y biológicos sobre cada uno de los grandes grupos de artrópodos que la componen. Se hace un análisis comparativo de la diversidad de troglobiontes y estigobiontes entre las distintas islas del archipiélago. ABSTRACT The different types of habitable underground environments existing in volcanic terrains are listed, with special emphasis on the different types of mesocavern networks (mesovoid shallow substratum, scree, pyroclastic deposits) and macrocaverns (lava tubes, volcanic pits, emptied dikes). A table of cave richness in the islands of Macaronesia is presented, and the environmental parameters of volcanic caves are analyzed. The types of adaptations of the subterranean fauna are discussed, and data on the diversity of such fauna in the Canary Islands are provided, with taxonomic and biological comments on each of the arthropods orders included. A comparative analysis of the troglobiont and stygobiont diversity among the different islands of the archipelago is made.
... Though their scales of interest differ vastly, these two examples have sought the same comfort from caves: a stable and sheltered environment, protected from the woes of the surface world. Since the discovery of lava caves on Mars (see (Sauro et al., 2020) for a review), they have become of renewed interest as targets for human shelter in future missions, as well as areas of astrobiological interest, with the potential of harboring traces of extant or extinct extraterrestrial life. ...
... As a result, the majority of Earth's cave systems are mainly represented by carbonate rocks, even if remarkable karst phenomena occur in gypsum, halite, and poorly soluble rocks such as quartzites (Wray and Sauro 2017). A significant number of caves are also hosted in lava fields, with classical lava tubes being the most representative (Sauro et al. 2020). ...
Article
Full-text available
Caves are among the most visited geological features in the world, attracting over 70 million people every year in more than 1,200 caves worldwide, and amounting up to 800 million Euros in entrance fees alone. The global business of show caves employs roughly 25,000 people directly (management, guides), and at least 100 times more people if we consider the connected tourist activities (souvenir shops, local transport, travel agencies, restaurants, and bars). It is estimated that the whole show cave business has a global commercial value of roughly 2 billion Euros, a number that is increasing constantly. Show caves are generally fragile ecosystems, and care should be taken in their management to safeguard their value for future generations. The international scientific (speleological) community has issued international guidelines for the sustainable development and management of show caves eight years ago, but their application is still far from being applied globally, especially in developing and least developed countries. Cave tourism is expected to increase, especially in countries where caves are abundant but not yet considered as tourist attractions, and where economic and political instability slow down the development of tourism. There are still a lot of possibilities for the opening of new show caves, especially in countries with low Gross Domestic Income (GDI), but their management needs to be sustainable, so that caves become a means of sustaining local economies, educating people on these fragile geo- and ecosystems, and protecting contemporarily their scientific and cultural heritage for future generations.
... Recently, there has been increasing interests in the exploration of Martian volcanic (lava tube) as compelling astrobiological targets (Léveillé and Datta, 2010;O'Connor et al., 2021;Popa et al., 2012;Sauro et al., 2020). One of the interesting questions for future missions (Phillips-Lander et al., 2021) is to find evidence of water-rock interactions to get insights on whether liquid water was present in the Martian caves over geologic time, as water is essential to the life that we know of. ...
Article
Volcanic (lava tube) caves at Lava Beds National Monument (N. CA, USA) provide a valuable terrestrial analog for volcanic caves on Mars and the Moon. Terrestrial volcanic caves host a diverse microbial life, liquid water, and a variety of secondary mineral deposits (speleothems) with diverse morphologies and chemical compositions. Speleothems may preserve records of past and present microbial life and signatures of paleoenvironmental changes in terrestrial volcanic caves. Distinguishing between speleothems via chemical processes and microbially-mediated processes in terrestrial volcanic caves will provide valuable insights for future exploration of martian volcanic caves. To elucidate the formation of speleothems, we studied the chemical makeup (inorganic and organic) of cave waters in seven volcanic caves of variable ages, temperature, moisture content, light intensity, and frequency of human visitation. Cave water was characterized by stable isotopic composition (δ¹⁸O and δ²H), concentrations of major and trace elements, cations, anions, and characteristics of dissolved organic matter (DOM). A forward reaction model (PHREEQC) was used to test possible pathways for secondary mineral precipitation that formed these speleothems. The source of cave water was primarily regional meteoric precipitation that entered the caves through cave openings or through the cave overburden and fractured basalt walls as indicated by cave floor puddle water line δ²H = 8.32*δ¹⁸O + 9.55 parallel to the global meteoric water line (GMWL, δ²H = 8.3*δ¹⁸O + 10). A line formed by cave ceiling drip water δ²H = 3.39*δ¹⁸O – 44.77 intersecting the GMWL indicated that the water may be undergoing evaporation within the caves. Silicate weathering was found to be a primary process resulting in cave water enriched in Si (22 ± 7 mg/L), and contained trace levels of Al, Fe, Zn, Li, Sr, Cu, B, V, Ba, Cr and Mn. Geochemical calculations indicated that cave waters were undersaturated with respect to both amorphous silica (SiO2am) and calcite (CaCO3) which were the major components of speleothems observed within the caves. Results of a forward reaction model showed that evaporation of cave waters could lower the solubility of SiO2am and CaCO3 by increasing their saturation and ultimately precipitate these two secondary minerals forming the speleothems. The cave water DOM was characterized by high concentrations of dissolved organic carbon (DOC, 12 ± 8 mg/L) with a molar C/N ratio ranging from 2 to 22. The DOM was found to be aromatic (SUVA254, 1.2–2.9 L/mg.m), terrestrially derived and humic-like (humification index, 7–26) and contained molecules of 100 Da and 5000 Da approximate molecular weight (AMU). Our results indicated that the terrestrially derived carbonaceous organic matter transported into the caves was not utilized for heterotrophic microbial metabolisms as DOC was accumulated over dissolved inorganic carbon (DIC). Both findings suggest that with minimal heterotrophy, chemo-litho-autotrophy may be important pathways that cycle the elements within these volcanic caves with low light conditions. Together, this study proposes a potential pathway of speleothem precipitation through the interaction of water, dissolved mineral constituents, and microbial life where dissolved ions are concentrated in cave drip water through cyclic condensation-vaporization processes. This work is part of a multi-disciplinary project Biologic Resource Analog in Low Light Environments (BRAILLE) funded by the NASA PSTAR Program (NNH16ZDA001N), which focuses on studying volcanic caves as terrestrial analogs for the Moon and Mars.
... These caves have been studied by remote sensing and have not been explored by dedicated missions, although some were proposed and developed, such as Moon Diver [53] and rock climber Lemur [54]. Lava tubes have been morphologically related to ones formed on Earth in volcanic rock by a volcanic eruption [55]. SISPO could be utilised for synthesising versatile sets of lavacaves images for (i) developing navigation algorithms and sampling spots detection by image processing (e.g., biological mats or their preserved remains on the geological substrate) or (ii) mapping the caves by photogrammetry for potential human settlements. ...
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This paper describes the architecture and demonstrates the capabilities of a newly developed, physically-based imaging simulator environment called SISPO, developed for small solar system body fly-by and terrestrial planet surface mission simulations. The image simulator utilises the open-source 3-D visualisation system Blender and its Cycles rendering engine, which supports physically based rendering capabilities and procedural micropolygon displacement texture generation. The simulator concentrates on realistic surface rendering and has supplementary models to produce realistic dust- and gas-environment optical models for comets and active asteroids. The framework also includes tools to simulate the most common image aberrations, such as tangential and sagittal astigmatism, internal and external comatic aberration, and simple geometric distortions. The model framework’s primary objective is to support small-body space mission design by allowing better simulations for characterisation of imaging instrument performance, assisting mission planning, and developing computer-vision algorithms. SISPO allows the simulation of trajectories, light parameters and camera’s intrinsic parameters.
... It has a length (L t ) of ∼7.6 km (of which ∼6.0 km are subaerial and ∼1.6 km submerged), with a total extension to ∼9.7 km when side branches and upper levels are considered. The conduit has a mean width (W t ) of ∼13.7 m and average height of ∼10 m and a total difference in topographical elevation of ∼374 m (∼310 m above current sea level and ∼64 m below it) (Sauro et al., 2020). ...
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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.
... The search for lava tubes and underground cavities on the Moon has been one of the core activities of lunar missions. In such lunar investigations, the presence of semi-collapsed lava tubes and intact lava tubes, which are substantially larger than the lava tubes found on Earth, was unfolded (Daga et al., 2009;Sauro et al., 2020). ...
Conference Paper
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In this paper, the seismic response of lava tubes was estimated. Several dimensionless numerical analyses were carried out for various dimensionless geometries. The effects of key influencing factors such as the depth of the lava tubes, the gravitational effect of the Moon, and the frequency content of the incident motion on the dynamic response of lava tubes were studied. The findings can be useful in geotechnical moonquake engineering and lunar seismology and provide some practical insights into the design of future moonquake-resilient human habitats on the Moon.
... Though their scales of interest differ vastly, these two examples have sought the same comfort from caves: a stable and sheltered environment, protected from the woes of the surface world. Since the discovery of lava caves on Mars (see (Sauro et al., 2020) for a review), they have become of renewed interest as targets for human shelter in future missions, as well as areas of astrobiological interest, with the potential of harboring traces of extant or extinct extraterrestrial life. ...
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Lava tubes on Mars hold exciting potential for the preservation of biosignatures, which may survive on geological timescales in these isolated, stable environments. To support the development of future astrobiological mission concepts, we turn to terrestrial lava tubes, host to a variety of microbial communities and secondary minerals. Following a multidisciplinary sampling protocol, we retrieved biological, molecular, and mineralogical data from several lava tubes in Iceland. We report on blue‐colored copper‐rich secondary minerals and their associated bacterial communities using a multi‐method approach, and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy data sets. We found numerous bacterial genera known for their high metal resistance and ability to survive in low‐nutrient environments. Both are characteristics to be expected for any potential life in Martian lava tubes, and should be considered when checking for contaminants in Mars mission preparations. Associated with the microbial mats, we identified several types of copper‐rich secondary minerals, indicating localized copper enrichments in the groundwater, possibly stemming from overlying ash deposits and nearby hyaloclastite formations. Molecular analysis revealed carotenoid signals preserved within the copper speleothems. If found in Martian lava tubes, blue copper‐rich mineral precipitates would be deserving of astrobiological investigation, as they have potential to preserve biosignatures and harbor life.
Chapter
Volcanic centers are complex, dynamic landforms. The stunning morphological variety of volcanic landforms is due to a combination of tectonic setting, eruption style, magma composition and volume, surface environment, and age, i.e., the time the landform has existed and evolved. The considerable variety of volcanic landforms reflects the large variability of these parameters. In turn, volcanoes affect their surrounding landscapes. The influence that volcanism exerts on a regional landscape is the result of many different factors. These include the nature and pattern of various fissures and vents, the length of time that volcanism is active, the relative age of volcanism, the composition and physical characteristics of extruded materials, the volume of erupted material, and the amount and extent of subsequent erosion. In some cases, voluminous lava flows and thick blanket tephras that accumulate over large areas may partially or entirely bury the preexisting landscape, whereas, in others, a focused distribution of lavas and tephras may produce a distinctive assemblage of lava-capped hills and mesas.
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Mars contains a large number of yet unexplained collapse features, sometimes spatially linked to large outflow channels. These pits and cavi are often taken as evidence for collapse due to the release of large volumes of pressurized groundwater. One such feature, Ganges Cavus, is an extremely deep (~ 6 km) collapse structure nested on the southern rim of Morella Crater, a 78-km-diameter impact structure breached on its east side by the Elaver Vallis outflow channel. Previous workers have concluded that Ganges Cavus, and other similar collapse features in the Valles Mariners area formed due to catastrophic release of pressurized groundwater that ponded and ultimately flowed over the surface. However, in the case of Ganges Cavus and Morella Crater, I show that the groundwater hypothesis cannot adequately explain the geology. The geology of Morella Crater, Ganges Cavus and the surrounding plains including Elaver Vallis is dominantly volcanic. Morella Crater contained a large picritic to komatiitic lava lake (> 3400 km ³ ), which may have spilled through the eastern wall of the basin. Ganges Cavus is a voluminous (> 2100 km ³ ) collapsed caldera. Morella Crater, Ganges Cavus and Elaver Vallis illustrate a volcanic link between structural collapse, formation and potential spillover of a large lake, and erosion and transport, but in this case, the geology is volcanic from source to sink. The geologic puzzle of Morella Crater and Ganges Cavus has important implications for the origins of other collapse structures on Mars and challenges the idea of pressurized groundwater release on Mars.
Chapter
We show how a GIS‐based approach on 3D morphologies can be used to analyze volume variations from the microscopic scale on rock samples to large collapse pits on Earth and Mars. The microscale analyses were performed on scans acquired by a confocal laser scanning microscope from carbonate rock plates dissolved by immersion in slightly acidic solutions. Each studied sample underwent an increasing number of immersions aiming to calculate the recession rate of such stones commonly used in cultural heritage when exposed to acidic rain. We achieved this by creating a synthetic reference surface and calculating the difference in height with the scanned sample surface. The same approach was applied in planetary remote sensing to evaluate the actual volume of collapsed conduit sections of Earth and Martian lava tubes from DEMs. Lava tubes can be up to tens of kilometers long on Earth and up to hundreds of kilometers on Mars but a numerical estimate of the collapse volumes (and thus of the voids) was never attempted. The creation of a synthetic surface on top of collapses best approximating the pristine topography and calculation of the volumes in between allows comparing the total volume of the collapsed sections in distinct planetary bodies.
Article
Caves and their entrances have been proposed as habitable environments and regions that could have preserved evidence of life, mostly due to their natural shielding from the damaging ionizing and non-ionizing radiation present on the surface. However, no studies to date have quantitatively determined the shielding offered by these voids on Mars. This paper describes the ultraviolet (UV) radiation environment in such environments by means of extensive radiative transfer (RT) model simulations applied to representative void geometries on Mars. The spatial and temporal characterization of the radiation field inside each void geometry is also performed. The RT model was previously tested against in situ Mars Science Laboratory UV observations on the Martian surface; the model showed excellent performance in terms of predicting the UV irradiances. The results presented here strongly suggest that pit craters and cave skylights are effectively shielded from the damaging UV radiation found on the Martian surface. In particular, locations on the floors of pit craters and skylights without cavernous spaces strongly attenuate UV irradiance at latitudes higher than ~45°; observing in several cases irradiances of the order of ~2% of those values found on the surface. Numerical simulations of cave entrances show a reduction even more than two orders of magnitude in UV radiation, both in the maximum instantaneous and cumulative doses, throughout the year and at any location of the planet. The attenuated UV irradiance in cavernous spaces remains stable in a 10 Myr timescale, while at the same time the photosynthetically active radiation is higher than the minimum required for Earth-like phototrophs. The intermediate radiation environment between the damaging radiation on the surface and the permanent darkness of a hypothetical cave offered by voids on Mars may represent favorable environments for habitability without constraining the type of energy source for potential as-yet unknown Martian organisms.
Chapter
Collecting quantitative data to support geological analysis and modelling is nowadays a fundamental requirement in all geology disciplines, including structural geology, stratigraphy, and geomorphology, on the Earth and on planetary bodies of the Solar System. In many cases the answer to this need is a Digital Outcrop Model (DOM), a Digital Elevation Model (DEM), or a Shape Model (SM): this can be a digital representation of an outcrop or topographic surface, or of a whole small body (asteroid or comet nucleus) for an SM, generally combined with imagery, that can be quantitatively visualized and studied in 3D, with the goal of obtaining quantitative measurements. 3D datasets and models for geological purposes include different complementary products: DEMs, DOMs, SMs, and subsurface models. The main differences among these different products are: (i) their nature, since DEMs, DOMs, and SMs represent relief surfaces showing outcropping geological structures that are completely accessible to characterization (up to some precision/resolution), while subsurface models reproduce inaccessible subsurface geological structures with some unavoidable level of uncertainty (hence they are models ); and (ii) their topology/dimensionality, as DEMs are actually 2.5D surfaces, generally covering large areas, DOMs are truly 3D surfaces, including multivalued reliefs (e.g. complex or overhanging reliefs, cliffs, caves, etc.), but are generally limited to smaller‐scale outcrops, and SMs are closed surfaces covering a whole small body, where subsurface models are essentially volumetric. In this volume we collect various examples of methods and techniques used to collect, analyze, and model 3D datasets, based on one or more supports (DEM, DOM, SM, subsurface model), and on different software tools, remote sensing, and modelling techniques. Reading the chapters authored by experts in different fields, it will become apparent that (i) the fundamental techniques allowing the production of DEMs, DOMs, and SMs through photogrammetry, laser scanning devices, and radar interferometry are well consolidated, and are almost seamlessly shared between the community of scientists working on the Earth and on planetary bodies of the Solar System; (ii) the particular way these techniques are applied in specific geological environments may change and, for instance, acquisition schemes in photogrammetry still represent a potentially critical issue; (iii) DOM, DEM, and SM processing, elaboration and analysis, including the analysis of image data associated with these surfaces, are active fields of research that are subject to continuous improvements; and (iv) the production of subsurface geological models based (also) on surface data is still not very common, particularly in planetary geology contexts. One of the aims of this volume is to disclose the numerous points that geological disciplines have in common in applications on the Earth and on planetary bodies of the Solar System, and to favor the communication and collaboration between different scientific communities.
Article
The next step for the exploration of space seems to require the human participation by means of a long-lasting lunar outpost. Therefore, this paper attempts to review the up-to-date knowledge regarding prominent issues surrounding the construction stage of a permanent base on the Moon in the light of the 3D printing process. In this context, a number of significant and specific issues are presented and discussed in a detailed manner to determine both the state-of-the-art position of the related literature and the relevant fields for improvement and implications. As a result, the use of heterogeneous and collective swarms of ground robots through a decentralized approach seems reasonable for the 3D printing tasks. However, as it is an emerging technology, it has to be improved further and tested in a terrestrial context as well as on the Moon. In this regard, it is a must to investigate precisely if the solar energy will be adequate for the operation of robots during preparation, transportation, and printing processes of local and Earth-based construction materials. In terms of structural needs, a composite shelter, including (i) an inner inflatable shell with a three-layer membrane, (ii) an outer concrete layer with regolith, polymer, and reinforcing fibers, and (iii) an outermost shield with raw regolith, will likely be viable. However, sieving and binding issues during the preparation phase of concrete under vacuum and microgravity conditions must be solved efficiently.
Chapter
Lava tubes exists as volcanic features not only on Earth, but even on other worlds. Lava tubes are the most practical and effective places where to install the first human bases on Mars. We review the human to Mars architectures currently being developed, subsequently we describe a context for the use of lava tubes for human habitation. The architecture for the use of in-situ resources as fuel for a return rocket, the use of a landing vehicle as the initial habitat are discussed. Also, the core landing site selection criteria are discussed, including how the access to a lava tube might change the landing approach. Additionally, the challenges to constructing a larger scale habitat for a growing population necessary to achieve a permanent base and the possible solutions are proposed. Whether lava tubes are present on the Martian surface, the shielding effect that they can provide is exceptionally advantageous in both logistical and economical terms for a planetary mission, since they do not require a huge mass load to be brought on a space mission and minimize considerably the work to be done on the dangerous Martian surface after landing—however, habitats on the surface still need to be considered where lava tubes are absent. Lava tubes can naturally protect from deadly radiations, extreme temperature variations, dust storms, and micrometeorite impacts. Thermal mining inside lava tubes is proposed as a realistic way to extract water ice from below the surface and use it for living purposes. Robots and humans should work together in order to detect and access the best lava tube close to the selected landing site. Lava tubes on Earth or the Moon can result in a great opportunity for conducting analog Martian missions.
Thesis
Los tubos de lava pueden ser considerados como potenciales refugios para las primeras colonizaciones en Marte y la Luna, pues brindan la posibilidad de salvaguardarse ante los mayores desafíos a los cuales se enfrentarían los primeros colonizadores. Los túneles de lava son conductos subterráneos formados durante erupciones volcánicas efusivas, con presencia de lava basáltica muy caliente y fluida, en pendientes suaves. Su formación es el resultado de uno de los siguientes mecanismos: (1) Formación de un techo solido sobre el flujo de lava; (2) Acreción progresiva de porciones marginales de lava solidificada que permite el desarrollo de techos arqueados sobre el flujo de lava; (3) Agregación de fragmentos móviles (usualmente placas o laminas arqueadas) de corteza ya solidificada que favorecen la formación de un techo sobre el flujo de lava; y (4) Extensión progresiva de los lóbulos producto de la lava pahoehoe. Un aspecto importante es que estas estructuras no son exclusivas de la tierra, por el contrario, se ha determinado a través de las distintas misiones espaciales, que pueden originarse en otros cuerpos del sistema solar, evidencias de ello se han registrado en algunas zonas volcánicas lunares como el Marius Hills, Mare Ingenii y Mare Tranquillitais; y en provincias volcánicas marcianas como los montes Olympus,Arsia,Pavonis y Ascraeus, además de Hardiaca Patera. A pesar de su potencialidad como refugios, su estudio y caracterización en términos de estabilidad y, por tanto, seguridad para ser habitados, es una tarea compleja debido a que aún no es posible realizar trabajo de campo en estas zonas. Por lo anterior, se propone la utilización de un análogo terrestre, a menor escala, que permita realizar una aproximación a los posibles escenarios de estabilidad a la cual se enfrentarían los primeros habitantes de la Luna y Marte. Se propone la utilización de los volcanes tipo escudo del archipiélago de las Galápagos como análogos de la Región de Tharsis, a una escala inferior. Esta analogía se propuso mediante la comparación conceptual entre estas dos zonas, a partir de la bibliografía consultada. Se concluyó que estas dos áreas tienen orígenes potencialmente similares, además de su similitud en términos de geomorfología y composición.
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Future permanent habitats on the Moon may facilitate space exploration by serving as an outpost for manned missions to other planets. Safety and resilience of those habitats are the main concerns, especially given the existing dangerous conditions and hazards such as temperature fluctuation, radiation, seismic activity, and meteorite impacts. Underground habitats in the form of “lava tubes” are good candidates for permanent human shelters because they provide immediate protection from such hazards. Evidence for their existence under the surface of the Moon is provided by GRAIL, SELENE spacecraft, and the LRO. Data from GRAIL suggests that the width of the lava tubes can be as large as 1–2 km. However, the size and geometry configurations under which the lava tubes are stable are not well-defined and there are no well-established criteria for their stability. The paper provides analytical and numerical …
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We report on evidence for fluid circulation in the upper crust of Mars, which could create environments favorable for life and its development. We investigate the nature of the thumbprint terrains covering part of Arcadia Planitia in the Martian northern hemisphere. Our analytic procedure allowed us to (i) hypothesise a potential relationship between these thumbprint terrains and an inferred underground fracture network that extends to where the clathrate-rich cryosphere contacts with the underlying hydrosphere; (ii) support the hypothesis that these thumbprint terrains are made of fine grained loosely packed materials erupted from deep beneath the subsurface mobilized by water; and (iii) date the thumbprint terrains of Arcadia Planitia to ~370 Ma. We conclude that the study area is an area worthy of astrobiological investigation, bringing water and fine grained sediment from depth to the surface for investigation.
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Lunar lava tubes have attracted special interest as they would be suitable shelters for future human outposts on the Moon. Recent experimental results from optical images and gravitational anomalies have brought strong evidence of their existence, but such investigative means have very limited potential for global mapping of lava tubes. In this paper, we investigate the design requirement and feasibility of a radar sounder system specifically conceived for detecting subsurface Moon lava tubes from orbit. This is done by conducting a complete performance assessment and by simulating the electromagnetic signatures of lava tubes using a coherent 3D simulator.The results show that radar sounding of lava tubes is feasible with good performance margins in terms of signal-to-noise and signal-to-clutter ratio, and that a dual-frequency radar sounder would be able to detect the majority of lunar lava tubes based on their potential dimension with some limitations for very small lava tubes having width smaller than 250 m. The electromagnetic simulations show that lava tubes display an unique signature characterized by a signal phase inversion on the roof echo. The analysis is provided for different acquisition geometries with respect to the position of the sounded lava tube. This analysis confirms that orbiting multi-frequency radar sounder can detect and map in a reliable and unambiguous way the majority of Moon lava tubes.
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Few traces of Earth’s geologic record are preserved from the time of life’s emergence, over 3,800 million years ago. Consequently, what little we understand about abiogenesis — the origin of life on Earth — is based primarily on laboratory experiments and theory. The best geological lens for understanding early Earth might actually come from Mars, a planet with a crust that’s overall far more ancient than our own. On Earth, surface sedimentary environments are thought to best preserve evidence of ancient life, but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last ~2,500 million years or more. By the time oxygenic photosynthesis evolved on Earth, Mars had been a hyperarid, frozen desert with a surface bombarded by high-energy solar and cosmic radiation for more than a billion years, and as a result, photosynthetic surface life may never have occurred on Mars. Therefore, one must question whether searching for evidence of life in Martian surface sediments is the best strategy. This Perspective explores the possibility that the abundant hydrothermal environments on Mars might provide more valuable insights into life’s origins.
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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.
Conference Paper
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With the goal of expanding human presence beyond Earth, sub-surface empty lava tubes on other worlds form ideal candidates for creating a permanent habitation environment safe from cosmic radiation, microm-eteorite impacts and temperature extremes. In a step towards Mars exploration , the Moon offers the most favorable pathway for lava tube exploration. In-depth analysis of GRAIL gravity data has revealed several candidate empty lava tubes within the lunar maria. The goal of this investigation is a proposed subsurface radar sounding mission to explore the regions of interest and potentially confirm the presence and size of buried empty lava tubes under the lunar surface.
Article
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We present an improved lunar digital elevation model (DEM) covering latitudes within ±60°, at a horizontal resolution of 512pixels per degree (∼60m at the equator) and a typical vertical accuracy ∼3 to 4m. This DEM is constructed from ∼4.5×109 geodetically-accurate topographic heights from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter, to which we co-registered 43,200 stereo-derived DEMs (each 1°×1°) from the SELENE Terrain Camera (TC) (∼1010pixels total). After co-registration, approximately 90% of the TC DEMs show root-mean-square vertical residuals with the LOLA data of <5m compared to ∼50% prior to co-registration. We use the co-registered TC data to estimate and correct orbital and pointing geolocation errors from the LOLA altimetric profiles (typically amounting to <10m horizontally and <1m vertically). By combining both co-registered datasets, we obtain a near-global DEM with high geodetic accuracy, and without the need for surface interpolation. We evaluate the resulting LOLA+TC merged DEM (designated as “SLDEM2015”) with particular attention to quantifying seams and crossover errors.
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The McBride Basalt Province covers approximately 5500 km 2 and is one of 11 discontinuous regions of Cenozoic volcanic rocks in north Queensland. These provinces are the northernmost part of a chain of volcanics that extend down the entire eastern coast of Australia, from the Torres Strait to southern Tasmania. These volcanics can be subdivided into central volcano provinces, lava field provinces and lesser leucitite provinces. The central volcano and leucitite provinces contain some felsic volcanics and form hotspot trails, whereas the lava field provinces are entirely mafic and do not have a well defined age-latitude relationship. All of the north Queensland provinces are of the lava field type and are centred around the Great Divide, suggesting a genetic relationship between the divide and the volcanic provinces. 164 eruption centres have been identified within the McBride Basalt Province. The majority of flows are less than 3 Ma, with the youngest volcano (Kinrara) being less than 50,000 y. Remnants of older flows of around 8 Ma occur in the southwest. A hiatus in eruptions is evident from 8 Ma to 3 Ma. Lavas from the 190,000 year old Undara volcano, cover about 1550 km 2. Undara crater is nearly circular with a diameter of around 330 m and is about 60 m deep. It forms the highest point of the McBride Basalt Province, at 1020 m a.s.l., although its low rim rises only 20 m above the surrounding lava field. Unusually for the McBride Province, the Undara vent does not have associated pyroclastic material. The longest of the Undara flows is some 160 km, with an average gradient of just 0.3°. Thermal insulation provided by the solidification of the crust above the actively flowing lava is required to produce flows of such length. In the distal regions, the confinement of the initial flows within pre-existing drainage channels also assists the development of such long flows. Lava tube caves occur up to 30 km from Undara crater, where the gradient is > 0.6°. Up to five successive flow units, demarcated by pahoehoe surfaces, can be seen in the walls of some caves. The caves developed by erosion through the lower units. Entrance to the caves is by steep collapse structures. Lava inflation features, such as lava-rise ridges and lava-rise pits, are common in the Undara flows. A particularly long lava-rise ridge, known as " The Wall " , extends for some 40 km. It is up to 20 high, and around 200 m wide. Formation was due to the inflation of a flow in a confined channel. Where a section of a flow solidifies, it is not underlain by actively flowing lava, so can not inflate. Where the surrounding region may undergo inflation, a depression is left at the level of the pre-inflation surface. Such lava inflation pits have more gently sloping sides than lava tube collapses and may contain pahoehoe floors that continue up their flanks. A series of lava-rise pits occur in close alignment to the main lava tube lines at Undara. In places, lava tubes head towards a depression, then are deflected around the solidified obstruction.
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The formation of lava tubes is a common phenomenon on some basaltic volcanoes, such as Etna. A model for tube formation by roofing of a channel is proposed and involves first describing lava as a Bingham liquid flowing down a slope. It is further assumed that lava flows in a channel with rectangular cross section: as a result of heat loss into the atmosphere, a crust is gradually formed on the upper surface of the flow and this crust eventually welds to the channel levées. We assume that a lava tube is formed when such a crust is sufficiently thick to resist the drag of the underlying flow and to sustain itself under its own weight. The minimum thickness of the crust satisfying such conditions depends on the tensile strength and shear strength of the crust itself. Assuming that the growth of the crust produces a downflow linear increase of the shear stress at the interface between flowing lava and the crust, the distance is evaluated between the eruption vent and the point where the tube is formed. The model predicts that if the flow rate is constant, the thickness of the flow increases as the crust fragments grow and weld to each other, and the velocity of the crust decreases to zero. Once the lava tube is formed, the initial flow rate can be achieved by a flow thickness smaller than the vertical size of the tube, with the same viscous dissipation: this may explain why under steady state conditions, the lava level inside a tube is frequently lower than the roof of the tube itself.
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Based on theoretical grounds, explosive basaltic volcanism should be common on Mars, yet the available morphological evidence is sparse. We test this hypothesis by investigating a unique unnamed volcanic field north of the shield volcanoes Biblis Patera and Ulysses Patera on Mars, where we observe several small conical edifices and associated lava flows. Twenty-nine volcanic cones are identified and the morphometry of many of these edifices is determined using established morphometric parameters such as basal width, crater width, height, slope, and their respective ratios. Their morphology, morphometry, and a comparison to terrestrial analogues suggest that they are martian equivalents of terrestrial pyroclastic cones, the most common volcanoes on Earth. The cones are tentatively interpreted as monogenetic volcanoes. According to absolute model age determinations, they formed in the Amazonian period. Our results indicate that these pyroclastic cones were formed by explosive activity. The cone field is superposed on an old, elevated window of fractured crust which survived flooding by younger lava flows. It seems possible that a more explosive eruption style was common in the past, and that wide-spread effusive plain-style volcanism in the Late Amazonian has buried much of its morphological evidence in Tharsis.
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Inflated pahoehoe sheet flows have a distinctive horizontal upper surface, which can be several hundred meters across, and are bounded to steep monoclinal uplifts. The inflated sheet flows studied ranged from 1 to 5 m in thickness, but initially propagated as thin sheets of fluid pahoehoe lava, generally 20-30 cm thick. The morphology of the lava as flow advanced is described. Inflated sheet flows from Kilauea and Mauna Loa are morphologically similar to some thick Icelandic and submarine sheet flows, suggesting a similar mechanism of emplacement. -from Authors
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Lunar sinuous rilles are large (kilometers long; tens of meters wide) channels commonly found on the lunar maria. Although there is broad consensus that sinuous rilles were generated during lava-flow emplacement, disagreement remains regarding the relative contributions of erosional and constructional processes during rille formation. Careful mapping of portions of Rima Marius (centered at 16.37°N, 49.54°W) using Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images with resolutions as high as 0.5 m/pixel reveal morphologic evidence for the origin of sinuous rilles. Specifically, shallow (<10 s of meters), narrow (< 500 m wide) rilles (herein called “rillettes”) are observed to anastamose around, and be cross-cut by, the main rille of Rima Marius. We interpret these rillettes to represent the early phases of emplacement of a sheet-like lava flow with a continuous surface crust (similar to terrestrial compound pahoehoe lava flows), in which flowing lava became concentrated into preferred pathways: the rillettes represent those early, and subsequently abandoned, preferred lava pathways. As the eruption continued, lava flow concentrated into a single lava tube (Rima Marius). Observations of active lava tubes at Kilauea volcano, Hawaii, indicate that basaltic lava flowing through an established lava tube can erode the underlying surface, even while the lava is advancing in a laminar fashion, and we infer similar processes occurred at Rima Marius. Thus, the rillettes represent an early, constructional phase of sinuous rille formation, and Rima Marius formed by subsequent downcutting caused by thermal and mechanical erosion.
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Intact lunar lava tubes offer a pristine environment to conduct scientific examination of the Moon's composition and potentially serve as secure shelters for humans and instruments. We investigated the SELENE Lunar Radar Sounder (LRS) data at locations close to the Marius Hills Hole (MHH), a skylight potentially leading to an intact lava tube, and found a distinctive echo pattern exhibiting a precipitous decrease in echo power, subsequently followed by a large second echo peak that may be evidence for the existence of a lava tube. The search area was further expanded to 13.00–15.005°N, 301.85–304.01°E around the MHH and similar LRS echo patterns were observed at several locations. Most of the locations are in regions of underground mass deficit suggested by GRAIL gravity data analysis. Some of the observed echo patterns are along rille A, where the MHH was discovered, or on the southwest underground extension of the rille.
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The 6-month long eruption at Holuhraun (August 2014–February 2015) in the Bárðarbunga-Veiðivötn volcanic system was the largest effusive eruption in Iceland since the 1783–1784 CE Laki eruption. The lava flow field covered ~ 84 km² and has an estimated bulk (i.e., including vesicles) volume of ~ 1.44 km³. The eruption had an average discharge rate of ~ 90 m³/s making it the longest effusive eruption in modern times to sustain such high average flux. The first phase of the eruption (August 31, 2014 to mid-October 2014) had a discharge rate of ~ 350 to 100 m³/s and was typified by lava transport via open channels and the formation of four lava flows, no. 1–4, which were emplaced side by side. The eruption began on a 1.8 km long fissure, feeding partly incandescent sheets of slabby pāhoehoe up to 500 m wide. By the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly pāhoehoe and ‘a’ā. The latter became the dominating morphology of lava flows no. 1–8. The second phase of the eruption (Mid-October to end November) had a discharge of ~ 100–50 m³/s. During this time the lava transport system changed, via the formation of a < 1 km² lava pond ~ 1 km east of the vent. The pond most likely formed in a topographical low created by a the pre-existing Holuhraun and the new Holuhraun lava flow fields. This pond became the main point of lava distribution, controlling the emplacement of subsequent flows (i.e. no. 5–8). Towards the end of this phase inflation plateaus developed in lava flow no. 1. These inflation plateaus were the surface manifestation of a growing lava tube system, which formed as lava ponded in the open lava channels creating sufficient lavastatic pressure in the fluid lava to lift the roof of the lava channels. This allowed new lava into the previously active lava channel lifting the channel roof via inflation. The final (third) phase, lasting from December to end-February 2015 had a mean discharge rate of ~ 50 m³/s. In this phase the lava transport was mainly confined to lava tubes within lava flows no. 1–2, which fed breakouts that resurfaced > 19 km² of the flow field. The primary lava morphology from this phase was spiny pāhoehoe, which superimposed on the ‘a’ā lava flows no. 1–3 and extended the entire length of the flow field (i.e. 17 km). This made the 2014–2015 Holuhraun a paired flow field, where both lava morphologies had similar length. We suggest that the similar length is a consequence of the pāhoehoe is fed from the tube system utilizing the existing ‘a’ā lava channels, and thereby are controlled by the initial length of the ‘a’ā flows.
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Mounting evidence from the SELENE, LRO, and GRAIL spacecraft suggests the presence of vacant lava tubes under the surface of the Moon. GRAIL evidence, in particular, suggests that some may be more than a kilometer in width. Such large sublunarean structures would be of great benefit to future human exploration of the Moon, providing shelter from the harsh environment at the surface—but could empty lava tubes of this size be stable under lunar conditions? And what is the largest size at which they could remain structurally sound? We address these questions by creating elasto-plastic finite element models of lava tubes using the Abaqus modeling software and examining where there is local material failure in the tube's roof. We assess the strength of the rock body using the Geological Strength Index method with values appropriate to the Moon, assign it a basaltic density derived from a modern re-analysis of lunar samples, and assume a 3:1 width-to-height ratio for the lava tube. Our results show that the stability of a lava tube depends on its width, its roof thickness, and whether the rock comprising the structure begins in a lithostatic or Poisson stress state. With a roof 2 m thick, lava tubes a kilometer or more in width can remain stable, supporting inferences from GRAIL observations. The theoretical maximum size of a lunar lava tube depends on a variety of factors, but given sufficient burial depth (500 m) and an initial lithostatic stress state, our results show that lava tubes up to 5 km wide may be able to remain structurally stable.
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Introduction: The Moon is the nearest celestial body to the Earth. As such, it has long been investigated to understand its formation and evolution, as a paradigm for better understanding the terrestrial planets, as well as all airless bodies in our solar system (e.g., Vesta, Phobos). The Moon's proximity to the Earth--more than one hundred times closer than any planet -- makes it a convenient target for exploration by spacecraft. Since the dawn of the space age in the previous century, we have explored the Moon with several spacecraft and even succeeded in sending astronauts there. One of the lessons of those explorations that hinders any future lunar expeditions is the severe conditions on the lunar surface. The lack of an atmosphere (10-12 torr) means that cosmic/galactic/solar rays, as well as the many micrometeorites directly striking the surface; in addition, surface temperatures vary widely, over a day-night range of more than 300 K. © 2012 Springer-Verlag Berlin Heidelberg. All rights are reserved.
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Pit crater chains are common topographic features on Mars and several other planetary bodies, and a wide range of mechanisms has been proposed for their origin. Two rifting-related seismic events in 1975-1976 and 1978 along the Mid-Atlantic Ridge near the northern coast of Iceland, associated with the Krafla volcanic eruptions to the south, produced an array of pit chains in unconsolidated sediments overlying Holocene basalt flows. Fault scarps and extension fractures in basaltic lava flows are traceable laterally into overlying unconsolidated fluvial deposits, revealing contrasting deformation styles in the two mechanical layers. Map-scale structures in basalt with little or no sedimentary cover include (1) fault scarps, (2) extension fractures and fracture swarms, (3) faulted monoclines, (4) widened fractures with caverns, and (5) localized circular or elongate collapse pits. Where unconsolidated fluvial sand and gravel deposits >3 m thick cover the basaltic lava flows, structural geomorphic features are dominated by (1) grabens bounded by normal faults with similar to 1 m displacement, (2) cone-to bowl-shaped pit craters with depths up to 2.8 m, and (3) elongate troughs. Formation of these structures in fluvial sediment was triggered by reactivation of faults and extension fractures in the underlying basalt. Pit craters are readily explained by downward "draining" of poorly consolidated material into subterranean cavities produced by fault and extension fracture dilation in underlying cohesive material (basalt). High-resolution imagery on Mars shows geomorphic patterns that are directly analogous to these Icelandic pit chains, suggesting similar processes have occurred on Mars.
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More than 100 pit craters in the Tharsis region of Mars exhibit morphologies, diameters, and thermal behaviors that diverge from the much larger bowl-shaped pit craters that occur in most regions across Mars. These Atypical Pit Craters (APCs) generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50–350 m, and high depth to diameter (d/D) ratios that are usually greater than 0.3 (which is an upper range value for impacts and bowl-shaped pit craters) and can exceed values of 1.8. Observations by the Mars Odyssey Thermal Emission Imaging System (THEMIS) show that APC floor temperatures are warmer at night and fluctuate with much lower diurnal amplitudes than nearby surfaces or adjacent bowl-shaped pit craters. Kīlauea volcano, Hawai'i, hosts pit craters that formed through subsurface collapse into active volcanic dikes, resulting in pits that can appear morphologically analogous to either APCs or bowl-shaped pit craters. Partially drained dikes are sometimes exposed within the lower walls and floors of these terrestrial APC analogs and can form extensive cave systems with unique microclimates. Similar caves in Martian pit craters are of great interest for astrobiology. This study uses new observations by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) and Context Camera to refine previous work where seven APCs were described from lower resolution THEMIS visible wavelength observations. Here we identify locations of 115 APCs, map their distribution across the Tharsis region, characterize their internal morphologies with high-resolution observations, and discuss possible formation mechanisms.
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Inflation of narrow tube-fed basaltic lava flows (tens of meters across), such as those confined by topography, can be focused predominantly along the roof of a lava tube. This can lead to the development of an unusually long tumulus, its shape matching the sinuosity of the underlying lava tube. Such a situation occurred during Kīlauea Volcano’s (Hawaiʻi, USA) ongoing East Rift Zone eruption on a lava tube active from July through November 2010. Short-lived breakouts from the tube buried the flanks of the sinuous, ridge-like tumulus, while the tumulus crest, its surface composed of lava formed very early in the flow’s emplacement history, remained poised above the surrounding younger flows. At least several of these breakouts resulted in irrecoverable uplift of the tube roof. Confined sections of the prehistoric Carrizozo and McCartys flows (New Mexico, USA) display similar sinuous, ridge-like features with comparable surface age relationships. We contend that these distinct features formed in a fashion equivalent to that of the sinuous tumulus that formed at Kīlauea in 2010. Moreover, these sinuous tumuli may be analogs for some sinuous ridges evident in orbital images of the Tharsis volcanic province on Mars. The short-lived breakouts from the sinuous tumulus at Kīlauea were caused by surges in discharge through the lava tube, in response to cycles of deflation and inflation (DI events) at Kīlauea’s summit. The correlation between DI events and subsequent breakouts aided in lava flow forecasting. Breakouts from the sinuous tumulus advanced repeatedly toward the sparsely populated Kalapana Gardens subdivision, destroying two homes and threatening others. Hazard assessments, including flow occurrence and advance forecasts, were relayed regularly to the Hawaiʻi County Civil Defense to aid their lava flow hazard mitigation efforts while this lava tube was active.
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Martian valley networks have been identified mainly in the Noachian heavily cratered uplands. Eight dense branching valley networks were studied in Noachian terrains of Huygens, Newcomb and Kepler craters, south Tyrrhena Terra, and Thaumasia, in Hesperian terrains of Echus Plateau and west Eberswalde craters, and in Amazonian terrains of Alba Patera, using images and digital elevation models from the Mars Express High Resolution Stereo Camera to determine 2D and 3D morphometric parameters. Extracted geomorphic parameters show similar geometry to terrestrial valleys: drainage densities, organization from bifurcation ratios and lengths ratios, Hack exponent consistent with terrestrial values of ~0.6, and progressive deepening of valleys with increasing Strahler order. In addition, statistics on valley depths indicate a deeper incision of Noachian valleys compared to younger post‐Noachian valleys (100 m for Noachian ones), showing a strong difference in fluvial erosion. These characteristics show that dense Martian valley networks formed by overland flows in relation to a global atmospheric water cycle in Noachian epoch and confirm that the later stages of activity may be related to shorter duration of activity, distinct climatic conditions, and/or regional processes, or conditions.
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Lunar Reconnaissance Orbiter Camera images reveal the presence of steep-walled pits in mare basalt (n = 8), impact melt deposits (n = 221), and highland terrain (n = 2). Pits represent evidence of subsurface voids of unknown extents. By analogy with terrestrial counterparts, the voids associated with mare pits may extend for hundreds of meters to kilometers in length, thereby providing extensive potential habitats and access to subsurface geology. Because of their small sizes relative to the local equilibrium crater diameters, the mare pits are likely to be post-flow features rather than volcanic skylights. The impact melt pits are indirect evidence both of extensive subsurface movement of impact melt and of exploitable sublunarean voids. Due to the small sizes of pits (mare, highland, and impact melt) and the absolute ages of their host materials, it is likely that most pits formed as secondary features.
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Skylights are openings on subsurface voids as lava tubes and caves. Recently deep hole structures, possibly skylights, were discovered on lunar photo images by the JAXA SELenological and ENgineering Explorer (SELENE)-Kaguya mission, and successively confirmed by the NASA Lunar Reconnaissance Orbiter (LRO) mission. Vertical hole structures and possibly underlying subsurface voids have high potential as resources for scientific study, and future unmanned and manned activities on the Moon. One mechanism proposed for their formation is impact cratering. The collapse of craters is due to the back spallation phenomena on the rear surface of the lava tube roofs. Previous analysis in this topic was based on small-scales laboratory experiments. These have pointed out that (i) the target thickness-to-crater diameter ratio is 0.7, and (ii) the projectile diameter-to-target thickness ratio is 0.16, at the ballistic limit once extrapolated to planetary conditions.
Article
Hydrovolcanism is a common natural phenomenon on Earth and should be common on Mars, too, since its surface shows widespread evidence for volcanism and near-surface water. We investigate fields of pitted cones in the Nephentes/Amenthes region at the southernmargin of the ancient impact basin, Utopia, which were previously interpreted as mud volcanoes. The cone fields contain pitted and breached cones with associated outgoing flow-like landforms. Based on stratigraphic relations,we determined aHesperian or youngermodel age.We test the hypothesis of a (hydro)volcanic origin. Based on a detailed morphological and morphometrical analysis and an analysis of the regional context, an igneous volcanic origin of these cones as hydrovolcanic edifices produced by phreatomagmatic eruptions is plausible. Several lines of evidence suggest the existence of subsurface water ice. The pitted cones display well-developed wide central craters with floor elevations below the preeruptive surface. Their morphometry and the overall appearance are analogous to terrestrial tuff cones and tuff rings. Mounds that are also observed in the same region resemble terrestrial lava domes. The hydrovolcanic interaction between ascending magma and subsurface water and/or water ice may explain the formation of the pitted cones, although other scenarios such as mud volcanism cannot be ruled out. Together with the mounds, the cones might represent effusive and explosive edifices of amonogenetic volcanic field composed of lava domes, tuff rings, tuff cones, and possibly maars.
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