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On developing thermal cave detection techniques for Earth, the Moon and Mars
Abstract
The purpose of this study is to (1) demonstrate the viability of detecting terrestrial caves at thermal-infrared wavelengths, (2) improve our understanding of terrestrial cave thermal behavior, (3) identify times of day when cave openings have the maximum thermal contrast with the surrounding surface regolith, and (4) further our understanding of how to detect caves on Earth, the Moon and Mars. We monitored the thermal behavior of two caves in the Atacama Desert of northern Chile. Through this work, we identified times when temperature contrasts between entrance and surface were greatest, thus enabling us to suggest optimal overflight times. The largest thermal contrast for both caves occurred during mid-day. One cave demonstrated thermal behavior at the entrance suggestive of cold-trapping, while the second cave demonstrated temperature shifts suggestive of airflow. We also collected thermograms without knowing optimal detection times; these images suggest both caves may also be detectable during off-peak times. We suggest cave detection using thermal remote sensing on Earth and other planetary objects will be limited by (1) capturing imagery in the appropriate thermal wavelength, (2) the size of cave entrance vs. the sensor's spatial resolution, (3) the viewing angle of the platform in relation to the slope trajectory of the cave entrance, (4) the strength of the thermal signal associated with the cave entrance, and (5) the time of day and season of thermal image capture. Through this and other studies, we will begin to identify the range of conditions under which caves are detectable in the thermal infrared and thus improve our detection capabilities of these features on Earth, the Moon and Mars.
... Cave entrances typically appear as warm features in thermal imagery acquired at night and cool features in midday imagery (e.g., [1,36,47,48]) because cave entrances are generally characterized by smaller diurnal temperature changes than the surrounding surface rock. Deep interior cave temperatures are typically stable (e.g., [49,50]) due to diurnal surface temperatures, which are dampened via thermal conduction of the geologic substrate [51,52]. ...
... This hypothesis went untested for over 30 years. Over the last decade, researchers have re-examined cave detection in the thermal infrared and have made significant advances (e.g., [1,47,[57][58][59][60]). ...
... Contemporary work involved collecting and analyzing ground-based temperature measurements and thermal imagery [1,47,[57][58][59]. The leap in our ability to detect caves was largely attributed to higher instrument sensitivity, modern computing systems that make processor-intensive analytical techniques possible, and the availability of high accuracy and affordable ground-based meteorological instruments. ...
Since the initial experiments nearly 50 years ago, techniques for detecting caves using airborne and spacecraft acquired thermal imagery have improved markedly. These advances are largely due to a combination of higher instrument sensitivity, modern computing systems, and processor intensive analytical techniques. Through applying these advancements, our goals were to: (1) Determine the efficacy of methods designed for terrain analysis and applied to thermal imagery; (2) evaluate the usefulness of predawn and midday imagery for detecting caves; and (3) ascertain which imagery type (predawn, midday, or the difference between those two times) was most informative. Using forward stepwise logistic (FSL) and Least Absolute Shrinkage and Selection Operator (LASSO) regression analyses for model selection, and a thermal imagery dataset acquired from the Mojave Desert, California, we examined the efficacy of three well-known terrain descriptors (i.e., slope, topographic position index (TPI), and curvature) on thermal imagery for cave detection. We also included the actual, untransformed thermal DN values (hereafter "unenhanced thermal") as a fourth dataset. Thereafter, we compared the thermal signatures of known cave entrances to all non-cave surface locations. We determined these terrain-based analytical methods, which described the "shape" of the thermal landscape hold significant promise for cave detection. All imagery types produced similar results. Down-selected covariates per imagery type, based upon the FSL models, were: Predawn-slope, TPI, curvature at 0 m from cave entrance, as well as slope at 1 m from cave entrance; midday-slope, TPI, and unenhanced thermal at 0 m from cave entrance; and difference-TPI and slope at 0 m from cave entrance, as well as unenhanced thermal and TPI at 3.5 m from cave entrance. Finally, we provide recommendations for future research directions in terrestrial and planetary cave detection using thermal imagery.
... Caves with large volume and greatest subterranean extent will be the highest priority targets for NASA. Researchers are actively developing techniques to understand how to detect caves on Earth and Mars, and searching for caves and cave‐like features on Mars using remote sensing analytical techniques.Rinker (1975, 2008a, 2008b) have improved the ability to detect caves on Earth.Cushing et al. (2007)has analyzed thermal and visible imagery to examine cave‐ like features on Arsia Mons, Mars.Keszthelyi et al. (2007)has identified lava tube remnants,Cushing et al. (2007)and Cushing and Titus (2010) have identified pit craters, andCabrol et al. (2009)has identified at least 677 features likely associated with speleogenesis including possible lava tubes, deep cavities associated with pit chains morphology, cracks associated with faulting, sink holes, and volcanic vents. Importance ofMartian Caves: (A)Caves may be important in the search for evidence of extraterrestrial life (Mazur 1978;Boston et al., 1992;Grin et al. 1998;Klein 1998;Boston 2000;Léveillé and Datta 2009) because caves offer protection from inhospitable surface conditions (Mazur 1978;Klein 1998;Cabrol et al. 2009). ...
... Terrestrial Cave Detection:Rinker (1975)provided a baseline for detecting caves in the thermal infrared, and suggested caves could be detected by identifying the thermal signal associated with the mass of air at the entrance contrasted against the surrounding ground surface. While air temperatures in cave entrances will be different from ambient temperatures,Wynne et al. (2008aWynne et al. ( , 2008b) suggest the basis for cave detection temperature will be the contrast between the rock walls within the cave entrance and external surface rock. Since Rinker's (1975) seminal work, advances have been made in terrestrial cave detection.Wynne et al. (2009)have shown it is possible to differentiate caves from cave‐like anomalies. ...
... Much larger amplitudes of diurnal and seasonal temperature shifts are expected on Mars. Because these shifts would occur widely and internal cave temperature is expected to be relatively constant, Martian cave detection is feasible using instrumentation to capture imagery at the appropriate wavelength and spatial resolution (Wynne et al. 2008a). We anticipate Mars atmospheric conditions will influence signal strength of Martian cave entrances resulting in a stronger thermal signal than their terrestrial counterparts. ...
... Lava-tube caves, by their nature, can protect inhabitants from all of the hazards that humans would encounter on the surface. Dust storms and micrometeoroids cannot reach cave interiors, temperature variations are minimized in cave environments (e.g., Boston et al., 2001;Wynne et al., 2008), and roof thicknesses of only 1 to 2 m can effectively shield against all types of incoming radiation (NCRP, 2001;De Angeles, 2002). ...
... Future thermal-infrared observations can provide important additional information about these caves that is not available at visible wavelengths. Diurnal and annual temperature variations inside a cave can be influenced by its depth and overall subsurface extent (e.g., Ingham et al., 2008;Wynne et al., 2008), and cave internal surface temperatures tend to represent the mean annual temperature at the surface (Cropley, 1965;Pflitsch and Piasecki, 2003;Wynne et al., 2008) unless complex heat-transport mechanisms, such as seasonal ventilation due to multiple entrances, exist. For example, deep caves that trap cold air should have mean internal surface temperatures that are lower than average, while short, shallow caves can be influenced by solar insolation at their entrances and have mean temperatures that are higher than average. ...
... Future thermal-infrared observations can provide important additional information about these caves that is not available at visible wavelengths. Diurnal and annual temperature variations inside a cave can be influenced by its depth and overall subsurface extent (e.g., Ingham et al., 2008;Wynne et al., 2008), and cave internal surface temperatures tend to represent the mean annual temperature at the surface (Cropley, 1965;Pflitsch and Piasecki, 2003;Wynne et al., 2008) unless complex heat-transport mechanisms, such as seasonal ventilation due to multiple entrances, exist. For example, deep caves that trap cold air should have mean internal surface temperatures that are lower than average, while short, shallow caves can be influenced by solar insolation at their entrances and have mean temperatures that are higher than average. ...
This paper presents newly discovered candidate cave entrances into
Martian near-surface lava tubes, volcano-tectonic fracture systems, and
pit craters and describes their characteristics and exploration
possibilities. These candidates are all collapse features that occur
either intermittently along laterally continuous trench-like depressions
or in the floors of sheer-walled atypical pit craters. As viewed from
orbit, locations of most candidates are visibly consistent with known
terrestrial features such as tube-fed lava flows, volcano-tectonic
fractures, and pit craters, each of which forms by mechanisms that can
produce caves. Although we cannot determine subsurface extents of the
Martian features discussed here, some may continue unimpeded for many
kilometers if terrestrial examples are indeed analogous. The features
presented here were identified in images acquired by the Mars Odyssey's
Thermal Emission Imaging System visiblewavelength camera, and by the Mars
Reconnaissance Orbiter's Context Camera. Select candidates have since
been targeted by the High-Resolution Imaging Science Experiment. Martian
caves are promising potential sites for future human habitation and
astrobiology investigations; understanding their characteristics is
critical for long-term mission planning and for developing the necessary
exploration technologies.
... En este sentido, el método preferible es la detección térmica de cuevas. Dicha detección se basa en el uso de imágenes del infrarrojo térmico que capturen el contraste de temperatura entre la cueva y el terreno circundante (Wynne et al., 2008). En la Tierra, y se supone que también en Marte, las cuevas presentan estabilidad termo-higrométrica en contraposición con el exterior que sufre mayores variaciones. ...
... En el trabajo experimental de Wynne et al. (2008) se estableció la viabilidad de la detección de cuevas utilizando el infrarrojo térmico, se mejoró nuestra comprensión del comportamiento térmico de las cuevas, se identificaron los tiempos de máximo contraste térmico, se establecieron protocolos de monitorización de temperatura, se identificaron los principales problemas relacionados con la longitud de onda óptima, con el ángulo óptimo de visión y con la resolución espacial de las imágenes térmicas. Sin embargo, Wynne et al. (2008) utilizaron una cámara térmica infrarroja manual en el desierto de Atacama, por lo que es necesaria más investigación en un método aerotransportado para la detección térmica de cuevas. Particularmente, utilizando este fundamento y las imágenes proporcionadas por el Mars Odyssey Thermal Emission Imaging System (THEMIS) se han detectado pozos verticales que parecen ser entradas a cuevas en una región volcánica de Marte (Cushing et al., 2007). ...
In this work we deal with an interesting paradox: caves, which were the habitat of man in prehistoric times and which are so important on Earth for many reasons, are also relevant in Planetary Geology and in space research, as they could provide shelter for future manned missions to Mars. Additionally, caves will be good candidates to search for life (present or past) on the Red Planet. In this work we review the types of caves that one can find on Earth according to their origin and lithology. This allows us to infer, by analogy, the kind of caves that one can expect to find on other celestial bodies of the Solar System, that is, extraterrestrial caves. We conclude this work with the current state of the art of our knowledge on extraterrestrial caves
... Although rarely used on Earth, in some cases these techniques have been useful for rapidly identifying possible cave entrances in densely forested areas using Lidarderived DEMs (Weishampel et al., 2011;Moyes and Montgomery, 2019). Especially thermal cave detection techniques are promising for identifying thermal contrasts between cave entrances or shelters and the areas more exposed to direct sunlight (Rinker, 1975;Wynne et al., 2008). These techniques have especially been used to identify CCEs in volcanic terrains on Mars, probably related to possible lava tubes: on Arsia Mons (Cushing et al., 2007), Ascraeus Montes, Pavonis, and Hadriaca Patera and many other areas on Mars (Léveillé and Datta, 2010;Cushing, 2012). ...
... RRIM maps eliminate the dependency of shaded relief images on incident light direction and emphasizes topographic convexity and concavity at the same time, facilitating the identification of karst features by shading the side slopes and lightening the divides of enclosed depressions. Furthermore, the use of LiDAR-derived DEMs and thermal-infrared sensors combined with UAV (unmanned aerial vehicle) acquisitions at high to very-high resolution (Rinker, 1975;Wynne et al., 2008;Melis et al., 2020), may improve the chance to identify sub-horizontal cave entrances difficult to detect from the vertical views of satellite images. ...
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.
... Finding a habitable environment depends on identifying these niches. In fact, excavation missions have yet to explore a large majority of planetary craters or dig underground and as such, suggesting the possibility an ecosystem for habitable living underneath Martian and lunar regolith [1]. ...
... Currently however, infrared thermal remotesensing methods can miss subsurface and subregolith regions. Wynne and Titus suggest cave detection using thermal remote sensing on Earth and other planetary objects are limited by (1) capturing imagery in the appropriate thermal wavelength, (2) the size of cave opening vs. the sensor's spatial resolution, (3) the viewing angle of the platform in relation to the slope trajectory of the surface, (4) the strength of the thermal signal associated with the surface opening, and (5) the time of day and season of thermal image capture. This may well be extended to search for crater niches that support life. ...
The search for life on the surface of Mars may focus on the detection of waste byproducts and thermal biomarkers associated with the conversion/consumption of energy required by all known lifeforms. In this paper, the authors examine the potential and limitations of using thermal biomarkers in the search for extraterrestrial life forms.
... Judson et al. [10] and Wynne et al. [11] demonstrated the viability of detecting terrestrial caves at thermal-infrared wavelengths and identified times of the day when cave openings have the maximum thermal contrast with the surrounding surface regolith and gave some ideas on how to detect caves on the Earth, the Moon and Mars. They monitored the thermal behaviour of two caves in the Atacama Desert and identified times when temperature contrasts between entrance and surface were greatest, thus suggesting optimal overflight times. ...
... This can be seen at the following pictures ( figure 10). 10 From a human point of view, this is acceptable and helps to distinguish even objects with small temperature differences but in the case of orthophoto generation, this is not usable. ...
This work aims to create new scientific knowledge by developing new innovative technology for remote detection of unknown underground cavities and deep-seated rockslides. To achieve the goal, we intend to develop new innovative technology for remote localization of unknown underground cavities and deep-seated rockslides using a thermal camera mounted on a unmanned aerial vehicle (UAV).
Technology is a defined sequence of operations and procedures under optimal conditions, varying within certain allowable limits, resulting in obtaining a particular result or product that meets certain requirements. Therefore, the development of new technology involves determining the allowable limits of deviation of the optimal conditions of operations and procedures for producing a good result that meets the established requirements. The development of new technology also involves determining the limits of its applicability under different external conditions. This paper includes determination of the allowable limits and the limits of applicability of the new technology being developed.
Until now, no technology has been developed for remote detection of unknown underground cavities or deep-seated rockslides. The goal of this work is the development of such innovative technology with numerous applications in construction, environmental studies and protection, security, defence and infrastructure.
... We identified several mud mounds that seemed to have cavities; one of them was chosen by the MARS2013 Mission Support Center Remote Science Support team to be observed by the field crew. Because a divergence of thermal inertias between ambient surfaces and cave entries is well known (e.g., Wynne et al., 2008), this particular cavity was selected due to its small size to test under unfavorable conditions, since larger caves exhibit a larger thermal inertia and maintain their temperature difference throughout longer periods. ...
... Hence, using thermal inertia measurements for identifying cave entry candidates should be applied with at least a basic understanding of the diurnal cycle of ground temperatures related to energy fluxes due to surface solar radiation fluxes, wind-driven heat exchanges, thermal emission behavior of the atmosphere, heat dissipation into the soil, and surface properties. Additionally, the detection efficiency also depends on the choice of the wavelength, cave entry size versus instrument footprint, viewing geometry, strength of the actual thermal signal, and the choice of the timing for obtaining the data (Wynne et al., 2008). ...
Martian caves are regarded as one of the most interesting locations in which to search for life on the planet. Data obtained during the MARS2013 expedition at Hamar Laghdad Ridge in the Tafilalt region of Morocco indicate that even small cavities can display thermal behavior that is characteristic for caves. For example, temperature in a cavity equaled 14°C±0.1°C before sunrise, which was higher than the temperature of the ambient air (10°C±0.1°C) and proximate rocks (9°C±0.1°C) at the same time. Within 30 min after sunrise, when the temperature of surrounding rocks corresponded to 15°C, this thermal relationship reversed. Measurements were conducted under simulated spaceflight conditions, including near-real-time interpretation of data that were acquired in a complex flight planning environment. We conclude that using ground-based thermal contrast measurements, in 7–14 μm band before and after sunset, is an effective method for Mars astronauts to identify caves, possibly superior to usage of space-based or ground-penetrating data.
Key Words: Mars—Caves—Thermal inertia—Detection—Human exploration.
Astrobiology 14, 431–437.
... Caves have also been identified mainly by the presence of ''skylights'', which can originate as openings in partially collapsed ceilings of lava tubes (e.g., Cushing et al., 2007). In addition to orbital imagery, thermal remote-sensing data can be used to distinguish thermal anomalies created by cave openings (Cushing et al., 2007;Wynne et al., 2008). Much of the interest in locating and studying Martian lava tubes and related flow features is in part due to the usefulness of such features in understanding the history and evolution of volcanism and global heat flux on Mars. ...
... More detailed efforts to identify lava tubes on Mars by orbiter data should be undertaken in conjunction with Earth-based remote-sensing of basaltic areas where caves are known to exist. For example, the thermal behavior of caves can be an ideal signature for remote detection (Cushing et al., 2007;Wynne et al., 2008). Radar instruments have already been used to probe the Martian subsurface from orbit on Mars Express and Mars Reconnaissance Orbiter, though at a resolution that is too low for detection of individual caves or lava tubes. ...
Cave minerals on Earth provide a record of aqueous processes and microbial activity. Caves, especially lava tubes, likely occur on Mars as well, and the minerals they contain may provide useful information on past aqueous activity and perhaps even martian
... Thus, much larger amplitudes of diurnal and seasonal temperature shifts are expected on Mars. Because these shifts would occur widely and internal cave temperature is expected to be relatively constant, Martian cave detection is feasible using imagery at the appropriate wavelength and spatial resolution [Wynne et al., 2008a]. We anticipate this will influence signal strength of Martian cave entrances resulting in a stronger thermal signal than their terrestrial counterparts. ...
... This will enable us to: (a) conduct best-fit regression analysis to identify optimal temperature contrasts between surface and the cave entrance. The latter approach is a time series technique equivalent to a Fast Fourier Transform [Wynne et al., , 2008a. Using this approach, we will model hourly temperature data by fitting temperature series as a function of local time of day. ...
... Aside from several researchers suggesting that caves exist on Mars (Boston, 2004b;Carr et al., 1977;Wynne et al., 2008), there is now some direct evidence of martian caves as well (Cushing et al., 2007a,b). Frederick et al. (2000) and Leveille and Datta (2010) hypothesized that martian lava tubes may harbor ice. ...
... During the daytime, the air in the cave, the cave walls, and the ice warm slightly due to the surrounding cave wall material. During most of the day atmospheric air cannot enter the cave because it is not dense enough, a phenomenon also observed by Wynne et al. (2008) for the non-ice caves of the Atacama desert on Earth. ...
We have developed a numerical model for assessing the lifetime of ice deposits in martian caves that are open to the atmosphere. Our model results and sensitivity tests indicate that cave ice would be stable over significant portions of the surface of Mars. Ice caves on Earth commonly occur in lava tubes, and Mars has been significantly resurfaced by volcanic activity during its history, including the two main volcanic provinces, the Tharsis and Elysium rises. These areas, known or suspected of having subsurface caves and related voids are among the most favorable regions for the occurrence of ice stability. The martian ice cave model predicts regions which, if caves occur, would potentially be areas of astrobiological importance as well as possible water sources for future human missions to Mars.
... In addition, TLS technology can be utilised for lunar cave measurements and data collection for creating digital terrain models. It should be noted that the utilisation of natural caves and lava tubes on the Moon could provide a natural shelter for future colonists [27,28]. Such solutions may provide living quarters with some protection against solar and gamma radiation, meteoroid impacts, and large temperature fluctuations (from −183 • C to +106 • C). ...
In the near future, permanent human settlements on the Moon will become increasingly realistic. It is very likely that the Moon will serve as a transit point for deep space exploration (e.g., to Mars). The key to human presence on the Moon is the ability to erect the necessary structures and habitats using locally available materials, such as lunar soil. This study explores the feasibility of using terrestrial laser scanning technology as a measurement method for civil engineering applications on the Moon. Three lunar soil simulants representing highland regions (LHS-1, AGK-2010, CHENOBI) and three lunar soil simulants representing mare regions (LMS-1, JSC-1A, OPRL2N) were used in this study. Measurements were performed using three terrestrial laser scanners (Z+F IMAGER 5016, FARO Focus3D, and Leica ScanStation C10). The research programme focused on the radiometric analysis of datasets from the measurement of lunar soil simulants. The advantages and limitations of terrestrial laser scanning technology for possible lunar applications are discussed. Modifications of terrestrial laser scanners that are necessary to enable their use on the Moon are suggested.
... • examine microbial life of tellurian caves as Mars analogs (e.g., Boston, 2004;Boston et al., 2006;Léveillé & Datta, 2010;Röling et al., 2015;Selensky et al., 2021;Westall et al., 2015); • model environments of terrestrial and potential martian cave systems (e.g., Schörghofer et al., 2018;Titus et al., 2010;Williams & McKay, 2015;Williams et al., 2010); • improve cave detection capabilities (e.g., Cushing et al., 2015;Hong et al., 2015;Pisani & De Waele, 2021;Wynne et al., 2008Wynne et al., , 2021); • develop and expand upon life detection instrumentation and techniques (e.g., Patrick et al., 2012;Preston et al., 2014;Storrie-Lombardi et al., 2011;Uckert et al., 2020); • expand the number of cave explorer robotic platforms under development (Green & Oh, 2005;Kesner et al., 2007;Morad et al., 2019;Nesnas et al., 2012;Parness et al., 2017;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021); • advance robotic sensing and navigational capabilities (e.g., Agha-Mohammadi et al., 2021;Kalita et al., 2017;Kim et al., 2021;Thakker et al., 2021); and, • propose mission concepts (e.g., Kerber et al., 2019;Phillips-Lander et al., 2020;Whittaker et al., 2021;Ximenes et al., 2012) and strategies to optimize future planetary cave exploration efforts (e.g., Rummel et al., 2014;Titus, Wynne, Boston, et al., 2021;Titus, Wynne, Malaska, et al., 2021;Wynne et al., 2014;Wynne, Titus, et al., 2022). values. ...
We provide the first solar system wide compendium of speleogenic processes and products. An examination of 15 solar system bodies revealed that six cave‐forming processes occur beyond Earth including volcanic (cryo and magmatic), fracturing (tectonic and impact melt), dissolution, sublimation, suffusion, and landslides. Although no caves (i.e., confirmed entrances with associated linear passages) have been confirmed, 3,545 SAPs (subsurface access points) have been identified on 11 planetary bodies and the potential for speleogenic processes (and thus SAPs) was observed on an additional four planetary bodies. The bulk of our knowledge on extraterrestrial SAPs is based on global databases for the Moon and Mars, which are bodies for which high‐resolution imagery and other data are available. To further characterize most of the features beyond the Moon and Mars, acquisition (preferably global coverage) and subsequent analysis of high‐resolution imagery will be required. The next few decades hold considerable promise for further identifying and characterizing caves across the solar system.
... Our collective knowledge has progressed from musing to confirming the presence of SAPs beyond Earth-not only on the Moon, but on at least 10 other planetary bodies . To date, detection capabilities have been developed and refined (e.g., Chappaz et al., 2017;Cushing, 2017;Pisani & De Waele, 2021;Wynne et al., 2008Wynne et al., , 2021, and astrobiological sampling techniques and associated instrumentation suites have been advanced by several key research projects (e.g., Agha-Mohammadi et al., 2021;Blank, 2020;Uckert et al., 2020). Moreover, a bevy of robotic platforms are slowly moving toward flight-qualified status (see Robotics section above), while astronauts are now being trained to conduct subsurface missions . ...
Nearly half a century ago, two papers postulated the likelihood of lunar lava tube caves using mathematical models. Today, armed with an array of orbiting and fly-by satellites and survey instrumentation, we have now acquired cave data across our solar system—including the identification of potential cave entrances on the Moon, Mars, and at least nine other planetary bodies. These discoveries gave rise to the study of planetary caves. To help advance this field, we leveraged the expertise of an interdisciplinary group to identify a strategy to explore caves beyond Earth. Focusing primarily on astrobiology, the cave environment, geology, robotics, instrumentation, and human exploration, our goal was to produce a framework to guide this subdiscipline through at least the next decade. To do this, we first assembled a list of 198 science and engineering questions. Then, through a series of social surveys, 114 scientists and engineers winnowed down the list to the top 53 highest priority questions. This exercise resulted in identifying emerging and crucial research areas that require robust development to ultimately support a robotic mission to a planetary cave—principally the Moon and/or Mars. With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable. Subsequently, we will be positioned to robotically examine lunar caves and search for evidence of life within martian caves; in turn, this will set the stage for human exploration and potential habitation of both the lunar and martian subsurface.
... Volcanic (lava tube) caves are common features on Earth found in large igneous provinces, shield volcanos and basaltic islands. The presence of igneous rocks and similar volcanic caves on Mars has been confirmed using remotely sensed images obtained from previous robotic exploratory missions (Hodges and Moore, 1994;Bandfield et al., 2000;Riedel and Sakimoto, 2002;Wyrick et al., 2004;Parcheta, 2005;Bleacher et al., 2021;Cushing et al., 2007;Keszthelyi and McEwen, 2007;Edwards et al., 2008;Wynne et al., 2008;Léveillé and Datta, 2010). Terrestrial volcanic caves provide a unique habitat for microbial life to flourish in the presence of liquid water Northup et al., 2001;Northup et al., 2011;Riquelme et al., 2015;Tomczyk-Żak and Zielenkiewicz, 2016;O'Connor et al., 2021), where harmful processes such as extreme weather (temperature, wind), desiccation, predation, UV radiation are reduced Barton, 2006). ...
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.
... Finally, other caves have also been investigated at the eastern edge of the hyperarid core (Wynne et al., 2008), a region much wetter due to its proximity to the foothills of the Andes. Here, infrared thermal imaging was confirmed as a tool to detect caves entrances on Mars (Cushing et al., 2007). ...
The Atacama Desert is by far the driest and oldest desert on Earth, showing a unique combination of environmental extremes (extreme dryness, the highest UV radiation levels on Earth, and highly saline and oxidizing soils), explaining why the Atacama has been largely investigated as a Mars analog model for almost 20 years. Based on the source and the amount of water available for life and its analogy with Mars, two ecosystems are of interest in the Atacama: its Coastal Range and the much drier hyperarid core, which we here review in detail. Members of the three domains of life have been found across these ecosystems living at the limit of habitability, suggesting the potential dry limits for each domain and also unveiling the highly patchy distribution of microbial life in its most extreme regions. The thorough study of the Atacama has allowed us to understand how life has adapted to its extreme conditions, the specific habitats that life occupies in each case (thus suggesting the most likely places in which to search for evidence for life on Mars), and the number of biosignatures detected across this desert. Also, the characterization of west-to-east transects across this desert has shown to be of significant value to understand the potential adaptations that Martian microorganisms may have followed in an ever-drying planet. All of this explains why the Atacama is actively used as the testing ground of the technologies (detection instruments, rovers, etc.) that were sent and will be sent to Mars. We also highlight the need to better inform the exact locations of the sites studied to understand general trends, the need to identify the true native microbial species of the Atacama, and the impact of climate change on the most arid and most Martian desert of Earth.
... Almost all previous studies of the possibilities of remote location of caves with thermal infrared cameras are made on previously known caves and are aimed on https://doi.org/10.52215/rev.bgs.2021.82.3.225 demonstration of the potential to locate caves (Rinker, 1975;Judson et al., 2008;Wynne et al., 2008;Muhlestein, 2012;Baroň, et al., 2013), rather than to make thermal infrared survey for location of new caves. The aim of our study is to develop a technology for remote location of new caves by thermal infrared camera mounted on a UAS and to make survey for location of new unknown caves by this technique (Shopov, 2013(Shopov, , 2017. ...
Here, for the first time in Bulgaria, we demonstrate that aerial survey of the terrain with a coaxial thermal and visible camera mounted on an UAS can detect much larger number of entrances to underground cavities and deep seated faults than a detailed systematic ground survey by experienced personnel. Thus geophysical problems are solved with these remote sensing methods. It is extremely promising and reveals great opportunities for improving techniques for location of unknown caves and deep seated faults to a much higher level. Obtained results are a significant step forward in the state-of-the art.
... Thus, much larger amplitudes of diurnal and seasonal temperature shifts are expected on Mars. Because these shifts would occur widely and internal cave temperature is expected to be relatively constant, Martian cave detection is feasible using imagery at the appropriate wavelength and spatial resolution (Wynne et al. 2008a). We anticipate this will influence signal strength of Martian cave entrances resulting in a stronger thermal signal than their terrestrial counterparts. ...
... Indeed, it may be possible to use the basalt walls of the tube as a heat sink to avoid the difficulty designing thermal radiators to face away from the Sun, and to keep them free of dust. [3] The intrusion of dust is problematic for its effects on health, and the damaging effects on technology. It forces crew to divert time to working to keep the habitat/lab clean rather than on mission objectives. ...
NASA's new lunar exploration program is the Artemis Program. As human space exploration evolves toward a permanent presence on the lunar surface, In-situ Resource Utilization will become increasingly important. The CLPS program supports the Artemis Program through the development and deployment of small robotic landers and rovers. These new lunar micro-rovers will be launching over the next several years to gather information about and conduct scientific research on the lunar surface. With the goal of expanding human presence beyond Earth, buried empty lava tubes on other worlds form ideal candidates for creating a permanent habitation environment. The lunar surface, unprotected by an atmosphere, is vulnerable to both direct and secondary meteoroid impacts and is exposed to cosmic and solar particle radiation that pose severe challenges to a lunar base on the surface. With multiple layers of lava basalt forming a meters thick roof, buried empty lava tubes can supply a safe zone away from life-threatening conditions. This paper will be dealing with design of LUnar LAva tube Discoverer (LULAD) instrument, which will help to further explore the regions of interest and potentially validate the existence of candidate lava tubes on lunar's surface.
... The importance of having thermal infrared observations in confirming caves is well-established [85,88] but the presently operational thermal sensors around Mars do not have sufficient spatial resolutions to confirm the meter-scale cave openings. Future orbiter, rover, and even UAV missions for Mars should try accommodating high-resolution thermal sensors as payloads. ...
Volcanic-aeolian interactions and processes have played a vital role in landscape evolution on Mars. Martian lava fields and associated caves have extensive geomorphological, astrobiological, and in-situ resource utilization (ISRU) implications for future Mars missions which might be focused on subsurface exploration. Although several possible cave “skylights” of tens to >100 m diameter have been spotted in lava fields of Mars, there is a possibility of prevalence of meter-scale features which are an order of magnitude smaller and difficult to identify but could have vital significance from the scientific and future exploration perspectives. The Icelandic volcanic-aeolian environment and fissure volcanoes can serve as analogs to study lava flow-related small caves such as surface tubes, inflationary caves, liftup caves, and conduits. In the present work, we have tried to explore the usability of unmanned aerial vehicle (UAV)-derived images for characterizing a solidified lava flow and designing a sequential methodology to identify small caves in the lava flow. In the mapped area of ~0.33 km2, we were able to identify 81 small cave openings, five lava flow morphologies, and five small cave types using 2 cm/pixel high-resolution images. The results display the usefulness of UAV imaging for such analogous research, and also highlight the possibility of the widespread presence of similar small cave openings in Martian lava fields. Such small openings can facilitate optimal air circulation within the caves while sheltering the insides from physical weathering and harmful radiations. Using the available best resolution remote sensing images, we extend the analogy through the contextual and geomorphological analysis of several possible pit craters in the Tharsis region of Mars, in a region of extremely vesicular and fragile lava crust with pahoehoe-type morphology. We report two possible pit craters in this region, with diameters as small as ~20 m. The possibility that such small cave openings can lead to vast subterranean hollow spaces on Mars cannot be ruled out considering its low gravity.
... Gunn et al. (2008) detected abandoned mineshafts in former mining areas after a TIR survey in Great Britain. To our knowledge, although several studies have assessed the potentiality of the TIR method for the characterization of subsurface cavities (Rinker, 1975;Wynne et al., 2008;Lee et al., 2016), few is known about the origin of the observed thermal anomalies, especially when slight subsidence is observed. As a consequence, the methodology to adopt to detect these objects before a collapse event remains unclear. ...
This work presents for the first time associated thermal anomalies and deformations over subsurface cavities/voids located within two harbour quays in Le Havre Harbourg, Normandy, France. An U.A.V. (Unmanned Aerial Vehicle) was used to acquire visible and thermal images over a diurnal cycle (from 7 a.m. to 5 p.m.). The visible images were processed to realize an altimetric model of the platforms by mean of the photogrammetric method, while the thermal infrared (TIR) images were used to study the evolution of their surface temperatures. The obtained 3D model shows the location of five topographic depressions on both quays. The analysis of the evolution of the surface thermal field leads to the detection of cold thermal anomalies that are 1) not correlated to surface properties, and 2) spatially associated to the flanks of the five topographic depressions. Using a 2D conductive-radiative model, we show that these anomalies are not directly due to the thermally insulating effect of an air-filled area. Finally, we conclude that preferential infiltration and subsequent evaporation in the micro-fracturation present within the flanks of the depressions may be responsible for the strong cooling of these zones.
... Hills and valleys in the Atacama desert are covered with extensive saline crusts of diverse types (Stoertz and Ericksen, 1974). Because it is the driest non-polar desert on Earth, the Atacama desert has been used as an analog for martian and lunar environments over the past two decades (e.g., Wettergreen et al., 1999;Navarro-Gonzales et al, 2003;Piatek et al., 2007;Wynne et al., 2008). ...
Over the past 50 years, our knowledge of the Moon has grown immensely. Progress in lunar science occurred through several phases. The first phase happened in the 1960s and 70s, during the Apollo and Luna missions, with the study of samples returned from the lunar surface. Petrological characterisation of lunar samples sparked the Lunar Magma Ocean concept, from which ensued the traditional view of the lunar crust and mantle organisation: the crust is plagioclase-rich, and its mafic content increases with increasing depth. The lunar mantle is commonly thought to be olivine-rich, like that of the Earth. The second lunar exploration phase happened in the 1990s, when satellites were launched into lunar orbit, collecting the first global remote sensing datasets. Owing to their wide to global coverage, remote sensing brought new insight into lunar science that is complementary to that provided by lunar samples. During the third, current phase of lunar exploration, new datasets were collected by spacecrafts orbiting the Moon between the 2000s and today. The remote sensing datasets acquired during the second and third phases of lunar exploration progressively complicated the initially simple picture that scientists drew from earlier studies. Indeed, high resolution remote sensing images and radar data led to the identification of volcanic features (domes, irregular mare patches), and the unambiguous discovery of volatiles in permanently shadowed regions and in lunar samples originating at depth in the Moon, demonstrating the Moon’s complex geological history. During this PhD, impact craters were used as natural drill holes through the lunar crust to sample material located underneath the surface. During impact, rocks from depth are emplaced in crater central peaks through elastic rebound, making it possible to investigate the composition of the crust at depth. Spectroscopic data from Chandrayaan-1’s Moon Mineralogy Mapper instrument were exploited to gather information on the composition of the crust in those central peaks. This work illustrates the use of remote sensing data on crater central peaks in order to constrain the shallow interior of the Moon. Remote sensing data can also be used to help locate which type of samples would need to be returned in the future from the lunar surface, in order to contribute to further elucidating the organisation of the lunar crust and upper mantle
... This creates a challenge because the openings come in many shapes and sizes, can be horizontal or vertically aligned, and may be occluded by rock outcroppings [29]. Attempts to locate these sites have employed airborne infrared thermal scanners to identify thermal variation around potential openings [30,31], while other endeavors used multispectral scans and electromagnetic sensors to distinguish possible anomalies associated with karstic features [32,33]. These techniques were hindered by coarse resolution or issues arising from variables such as vegetation cover or atmospheric processes. ...
Lidar (Light detection and ranging) scanning has revolutionized our ability to locate geographic features on the earth’s surface, but there have been few studies that have addressed discovering caves using this technology. Almost all attempts to find caves using lidar imagery have focused on locating sinkholes that lead to underground cave systems. As archaeologists, our work in the Chiquibul Forest Reserve, a heavily forested area in western Belize, focuses on locating potential caves for investigation. Caves are an important part of Maya cultural heritage utilized by the ancient Maya people as ritual spaces. These sites contain large numbers of artifacts, architecture, and human remains, but are being looted at a rapid rate; therefore, our goal is to locate and investigate as many sites as possible during our field seasons. While some caves are entered via sinkholes, most are accessed via vertical cliff faces or are entered by dropping into small shafts. Using lidar-derived data, our goal was to locate and investigate not only sinkholes but other types of cave entrances using point cloud modeling. In this article, we describe our method for locating potential cave openings using local relief models that require only a working knowledge of relief visualization techniques. By using two pedestrian survey techniques, we confirmed a high rate of accuracy in locating cave entrances that varied in both size and morphology. Although 100% pedestrian survey coverage delivered the highest rate accuracy in cave detection, lidar image analyses proved to be expedient for meeting project goals when considering time and resource constraints.
... Terrestrial caves are common on every continent and have multiple viable formation mechanisms. On Mars, caves have been hypothesized to exist as well (Carr et al., 1977;Boston, 2004;Wynne et al., 2008;Williams et al., 2010;Cushing, 2012). Martian cave formation processes are hypothesized to include mass-wasting (e.g., undercutting of scarps), soluble rock dissolution, tectonism and volcanic processes (e.g., lava tubes). ...
Infrasonic resonance has previously been measured in terrestrial caves by other researchers, where Helmholtz resonance has been suggested as the plausible mechanism resulting in periodic wind reversals within cave entrances. We extend this reasoning to possible Martian caves, where we examine the characteristics of four atypical pit craters (APCs) on Tharsis, suggested as candidate cave entrance locations. The results show that, for several possible cave air movement periods, we are able to infer the approximate cave volumes. The utility of inferring cave volumes for planetary cave exploration is discussed.
... Hills and valleys in the Atacama desert are covered with extensive saline crusts of diverse types ( Stoertz and Ericksen, 1974 ). Because it is the driest non-polar desert on Earth, the Atacama desert has been used as an analog for martian and lunar environments over the past two decades (e.g., Wettergreen et al., 1999;Navarro-Gonzales et al, 2003;Piatek et al., 2007;Wynne et al., 2008 ). ...
The identification and characterization of hydrated minerals within ancient aqueous environments on Mars are high priorities for determining the past habitability of the planet. Few studies, however, have focused on characterizing the entire mineral assemblage, even though it could aide our understanding of past environments. In this study we use both spaceborne and field (VNIR spectroscopy) analyses to study the mineralogy of various salt flats (salars) of the northern region of Chile as an analog for Martian evaporites. These data are then compared to laboratory based Raman and XRD analyses for a complete overview on mineral assemblages. Central (core) and marginal zones within the salars are easily distinguished on the Landsat 8 band color composites. These areas host different mineral assemblages that often result in different landscapes. The lower elevation Salar de Atacama, located in the Andean pre-depression, is characterized by a unique thick halite crust at its center, whereas various assemblages of calcium sulfates (gypsum, bassanite, anhydrite) and sodium sulfates (mirabilite, thenardite, blodite, glauberite), borates (ulexite, pinnoite), Al/Fe- clays and carbonates (calcite, aragonite) were found at its margin. Sulfates form the main crust of the Andean salars to the east, although various compositions are observed. These compositions appear controlled by the type of feeder brine (Ca, SO4 or mixed), a result of the local geology among other factors. Sulfate crusts were found to be generally thin (<5 cm) with a sharp transition to the underlying clay, silt, or sand-rich alluvial deposits. Coupled with morphologic analyses, VNIR spectroscopy provides a powerful tool to distinguish different salt crusts. XRD analysis allowed us to quantify the mineral assemblages and assess the limitations of VNIR techniques in the presence of hydrated sulfates, which tend to mask the signatures of other minerals such as clays, chlorides, and carbonates. We found that the Atacama's unique arid and volcanic environment, coupled with the transition recorded in some of the salars has a strong Mars analog potential. Characterizing the outcrop mineralogy at a variety of environments from alkaline, lake waters to more acidic salar brines may help in constraining geochemical environments on Mars.
... Beyond the obvious " cool factor " of extraterrestrial caves, the answer is simple. These features represent high-priority targets for future robotic [14, 15] and human missions [16, 17]. Martian and lunar caves can provide pre-existing sheltered environments for the construction of astronaut bases and/or storage facilities. ...
... Beyond the obvious "cool factor" of extraterrestrial caves, the answer is simple. These features represent high-priority targets for future robotic [14,15] and human missions [16,17]. Martian and lunar caves can provide pre-existing sheltered environments for the construction of astronaut bases and/or storage facilities. ...
... Thermal gradients between deep rock and colder ground surface often help cavers identify unexplored caves by searching for melted snow cover in the winter season (Rinker 1975;Lešinský 1999;Baroň 2002). The Infrared Thermography method (IRT) has been proposed as a useful tool for detecting karst cave openings (Rinker 1975, Wynne et al. 2008, Baroň et al. 2012) and hydrological features in karst watersheads (Campbell et al. 1996). ...
... For primary thermal surveying and for identifying sites with different temperature conditions, methods of infrared (IR) camera or IR thermometer temperature measurement are ideal because they do not involve contact and are environmentally friendly with no interior cave destruction. IR camera and IR thermometer were used in the research of cave thermal regimes by Marwin and Thompson (2005), Wynne et al. (2008) and Curtis and Kyle (2011). Clawson et al. (1980) used IR thermometers for monitoring ceiling rock and bat cluster temperatures in a cave environment. ...
The aim of this study was to evaluate the rock surface temperature (RST) regime in Kateřinská Cave in the Moravian Karst (Czech Republic, South Moravia) using nondestructive infrared methods. Air temperature monitoring was also included to quantify the dominant factors affecting the RST. Measurements were taken during the period covering January, 2010 to March, 2012. HOBO air temperature sensors with data loggers were placed in front of the cave entrance, in the entrance corridor and on selected sites in the cave interior. An infrared (IR) thermometer was used to measure the surface temperature of the solid rock. The RST in the cave interior during each season was also recorded by IR camera. The average temperature of the rock surface over the two year period was 6.95 °C. The longterm average of the RST was always 0.01 to 0.79 °C lower than the air temperature. The dynamics of the RST are most obvious at the entrance corridor to the cave, with temperature variability up to 17.34 °C. The dynamism of both the RST and air temperature decrease as the distance from the entrance increases. The lowest RST variability (1.19 °C) was detected at a distance of 271–280 meters from the entrance. The differences in the maximum RST in the monitored profile were relative small, ranging from 7.30 to 8.70 °C. Minimum temperatures in the cold season showed a significant difference among themselves. Changes in rock surface and air temperatures are dominantly influenced by air exchange with the external environment, although the RST may be locally influenced on a short-term basis by other factors, such as attendance and biota. Temperature heterogeneous zones over space in Kateřinská Cave with no air flow were located by thermal imaging. It is therefore an area where unknown spaces or exterior access can be expected.
... Other applications include the thermal mapping of rivers [13] and for agricultural applications including the identification of frost damage during cold nights [6]. Another application where small UAS are not currently utilized but would benefit is cave detection and identification [31]. ...
As Unmanned Aerial System (UAS) technology matures, the list of potential civilian applications continues to grow substantially. Currently, the majority of applications are centered around providing optical imagery, either in real-time video or high resolution mapping. But as more sophisticated applications are desired, the limitations of simple imagery are becoming more evident, especially for precision agricultural applications. However, recent advancements in UAS based precision agriculture have demonstrated the effectiveness of including thermal infrared (TIR) cameras. In many situations, decision support indicators are evident in the TIR spectrum, whereas they are undetectable in the visible light and near-infrared spectrum. In this paper, a survey of some of the applications under development utilizing TIR imagery is presented along with implementation strategies to provide guidance for researchers wishing to add TIR imagery into their applications.
... Such features appear to be a by-product of lava flows or dikes as they are here on Earth, and these can be made by a variety of mechanisms (Kempe et al., 2006;Kempe, 2009). Methods to refine remote detection of such features are being undertaken (e.g., Cushing et al., 2007;Wynne et al., 2008;Cushing, 2012). ...
A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR
Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn
from both the biological science and Mars exploration communities, focused on understanding when and where
Special Regions could occur. The study applied recently available data about martian environments and about
terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar
team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth—including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as ‘‘Uncertain’’ or ‘‘Special’’ as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.
... For broad-scale prospecting, airborne-or satellite-based remote sensing is necessary. Because caves have a more stable temperature than the surface environment, there has been an effort to use thermal remote sensing on earth (Griffith, 2000) and on other planets (Cushing et al., 2007;Wynne et al., 2008) to detect cave openings. Though a temperature gradient of 7.2 uC was detected on the ground 50 to 100 m away from cave openings in Belize (Griffith, 2001), this method is challenging, given the coarse resolution of most satellite thermal sensors. ...
Locating caves can be difficult, as their entranceways are often obscured below vegetation. Recently, active remote-sensing technologies, in particular laser-based sensor systems (LiDARs), have demonstrated the ability to penetrate dense forest canopies to reveal the underlying ground topography. An airborne LiDAR system was used to generate a 1 m resolution, bare-earth digital elevation model (DEM) from an archaeologically-and speleologically-rich area of western Belize near the ancient Maya site of Caracol. Using a simple index to detect elevation gradients in the DEM, we identified depressions with at least a 10 m change within a circular area of no more than 25 m radius. Across 200 km 2 of the karst landscape, we located 61 depressions. Sixty of these had not been previously documented; the other was a cave opening known from a previous expedition. The morphologies of the depressions were characterized based on the LiDAR-derived DEM parameters, e.g., depth, opening area, and perimeter. We also investigated how the measurements change as a function of spatial resolution. Though there was a range of morphologies, most depressions were clustered around an average maximum depth of 21 m and average opening diameter of 15 m. Five depression sites in the general vicinity of the Caracol epicenter were visited; two of these were massive, with opening diameters of ,50 m, two could not be explored for lack of climbing gear, and one site was a cave opening into several chambers with speleothems and Maya artifacts. Though further investigation is warranted to determine the archaeological and geological significance of the remaining depressions, the general methodology represents an important advancement in cave detection.
... Since caves are characterized as nutrient poor and aphotic, and often exhibit low climatic variability at depth, caves are indeed an extreme biome. Wynne et al. (2007Wynne et al. ( , 2008b have established that cave thermal behavior is influenced by surface temperatures. However, it is uncertain to what extent cave deep zones may be buffered from global climate change (Wynne et al. 2008a). ...
Four new species of presumed troglobitic polydesmidan millipeds in two new genera are described from caves in the states of Arizona, Nevada and California. Pratherodesmus, n. gen., is comprised of the type species, P. voylesi, n. sp., P. ecclesia, n. sp., and P. despaini, n. sp. The genus is found in Arizona and California. Nevadesmus ophimontis, n. gen., n. sp., is from White Pine Co., Nevada; the new genus also includes N. hubbsi (Chamberlin) 1943, new combination. All four species were collected in or near United States National Parks, Bureau of Land Management lands, and in a private preserve. All new taxa are authored by W. A. Shear only.
... Consequently, the dry hills of the Pacific Coastal Range have more benign sites for the development of microbial life, differing from the typical desert conditions associated to the Atacama. Only recently, caves in the arid areas of the Atacama have begun to be explored, and to date no microorganisms of any type have been described living inside them [51]. Here, we describe the presence of biofilms growing at mesophilic conditions at the dimmest lighted zone of a coastal cave of the Atacama Desert. ...
Caves offer a stable and protected environment from harsh and changing outside prevailing conditions. Hence, they represent an interesting habitat for studying life in extreme environments. Here, we report the presence of a member of the ancient eukaryote red algae Cyanidium group in a coastal cave of the hyperarid Atacama Desert. This microorganism was found to form a seemingly monospecific biofilm growing under extremely low photon flux levels. Our work suggests that this species, Cyanidium sp. Atacama, is a new member of a recently proposed novel monophyletic lineage of mesophilic “cave” Cyanidium sp., distinct from the remaining three other lineages which are all thermo-acidophilic. The cave described in this work may represent an evolutionary island for life in the midst of the Atacama Desert.
... Consequently, the dry hills of the Pacific Coastal Range have more benign sites for the development of microbial life, differing from the typical desert conditions associated to the Atacama. Only recently, caves in the arid areas of the Atacama have begun to be explored, and to date no microorganisms of any type have been described living inside them [51]. Here, we describe the presence of biofilms growing at mesophilic conditions at the dimmest lighted zone of a coastal cave of the Atacama Desert. ...
... Lava caves in Earthly volcanic terrains make an especially attractive extraterrestrial analog environment due to the presence of large amounts of basaltic terrain on Mars and the identification of lava caves on the surface in a number of Martian localities and on other Solar System bodies (Boston, 2004;Cushing et al., 2007;Wynne et al., 2008;Haruyama et al., 2009). The potential for such cavities on Mars to harbor substantial amounts of ice over geologically significant periods of time has been suggested (frederick et al., 2000) and strongly argued in a modeling study (Williams et al., 2010). ...
Lava caves represent a scientifically untapped habitat in which to study Earth’s microbial life and provide an outstanding environment in which to identify biosignatures for detecting life on other planets. Our studies of microbial mats and mineral deposits in lava caves in the Azores (Portugal), New Mexico, and Hawai‘i (USA) have revealed a wealth of bacterial diversity through molecular genetic analyses and scanning electron microscopy. Much of this bacterial diversity represents novel species, as well as novel higher taxonomic units, such as genera and families. Geochemical analyses of infiltrating water, soils, and rock walls suggest the presence of organic carbon that may fuel heterotrophy and reduce inorganic energy sources, such as iron, manganese, and sulfur to fuel chemolithotrophy. Scanning electron microscopy studies of mineral deposits, accompanied by molecular studies, reveals the presence of extensive biological morphologies in a variety of mineral deposits decorating lava cave walls. These studies provide a rationale for examining mineral deposits in lava caves on extraterrestrial bodies in the search for life or its remnants.
... Consequently, the dry hills of the Pacific Coastal Range have more benign sites for the development of microbial life, differing from the typical desert conditions associated to the Atacama. Only recently, caves in the arid areas of the Atacama have begun to be explored, and to date no microorganisms of any type have been described living inside them[51]. Here, we describe the presence of biofilms growing at mesophilic conditions at the dimmest lighted zone of a coastal cave of the Atacama Desert. ...
Caves offer a stable and protected environment from harsh and changing outside prevailing conditions. Hence, they represent an interesting habitat for studying life in extreme environments. Here, we report the presence of a member of the ancient eukaryote red algae Cyanidium group in a coastal cave of the hyperarid Atacama Desert. This microorganism was found to form a seemingly monospecific biofilm growing under extremely low photon flux levels. Our work suggests that this species, Cyanidium sp. Atacama, is a new member of a recently proposed novel monophyletic lineage of mesophilic "cave" Cyanidium sp., distinct from the remaining three other lineages which are all thermo-acidophilic. The cave described in this work may represent an evolutionary island for life in the midst of the Atacama Desert.
Thermal response of the surface to solar insolation is a function of the topography and the thermal physical characteristics of the landscape, which include bulk density, heat capacity, thermal conductivity and surface albedo and emissivity. Thermal imaging is routinely used to constrain thermal physical properties by characterizing or modeling changes in the diurnal temperature profiles. Images need to be acquired throughout the diurnal cycle – typically this is done twice during a diurnal cycle, but we suggest multiple times. Comparison of images acquired over 24 hours requires that either the data be calibrated to surface temperature, or the response of the thermal camera is linear and stable over the image acquisition period. Depending on the type and age of the thermal instrument, imagery may be self-calibrated in radiance, corrected for atmospheric effects, and pixels converted to surface temperature. We used an experimental instrumentation where the calibration should be stable, but calibration coefficients are unknown. Cases may occur where one wishes to validate the camera's calibration. We present a method to validate and calibrate the instrument and characterize the thermal physical properties for areas of interest. Finally, in situ high-temporal-resolution oblique thermal imaging can be invaluable in preparation for conducting overflight missions. We present the following:
•The use of oblique thermal high temporal resolution thermal imaging over diurnal or multiday periods for the characterization of landscapes has not been widespread but poses great potential.
•A method of collecting and analyzing thermal data that can be used to either determine or validate thermal camera calibration coefficients.
•An approach to characterize thermophysical properties of the landscape using oblique temporally high-resolution thermal imaging, combined with in situ ground measurements.
###### FULL TEXT ###### https://www.sciencedirect.com/science/article/pii/S0926580521004301?dgcid=coauthor ##### The exploration and conquest of the Moon and Mars is very likely in the near future. Therefore the erection of lunar and Martian structures, suitable for permanent human presence is increasingly discussed by the scientific community. Various concepts have been proposed for creation of lunar and Martian permanent bases. Techniques ranging from 3D printing of concrete, through utilization of natural caves to inflatable pressurized tensile structures are considered. In authors' opinion a fast, accurate and remote measuring technique will be necessary for successful completion of majority of extra-terrestrial construction tasks. The terrestrial laser scanning technique should be used for the lunar and Martian construction projects. To assess the suitability of terrestrial laser scanning techniques which are going to be used on the Moon and Mars, initial measurements should be conducted on Earth. Unfortunately extra-terrestrial soils are not available for general research. The only feasible solution is to use lunar and Martian soil simulants to practice construction technologies, techniques and strategies. The main aim of this research programme is radiometric and geometric analysis of TLS point clouds collected during the measurement of lunar and Martian soil simulants targets. The conducted research programme was focused on the analysis of a laser beam dispersion and absorption in soil simulants. It should be noted that the dispersion and absorption of a laser beam for the scanned surface is a key factor in TLS remote measurements. The advantages and limitations of TLS technique for possible lunar and Martian applications was discussed. Areas of subsequent research were pointed out. In the first section the brief state-of-the-art was given in context of the conducted research programme. Subsequently, in section two used specimens and equipment was described. The third section of the paper was dedicated to present the conducted research programme. The achieved results were shown in section four in the form of tables and graphs. Finally, in section five the discussion was carried out and followed by a list of drawn conclusions. It was proved that TLS technique can be used to effectively scan LSS and MSS, thus scanning on the Moon and Mars is enabled.
Speleology, Speleoarchaeology, Heritage Management, Algarve, Portugal
Humans have looked for extraterrestrial biosignatures on the surfaces of other planets and moons. These surfaces are often exposed to conditions and processes that exceed the physical limits of life, e.g., intense cosmic radiation, impact events, and large thermal extremes, that would render difficult the preservation of biosignatures over geologic time. Planetary caves provide protection from cosmic radiation, small-scale impact events, and have relatively stable thermal environments. These characteristics may well permit preservation of biosignatures over long periods of time and make them a prospective astrobiology target for biosignatures beyond Earth (Boston et al., 2001; Léveillé & Datta, 2010; Martins et al., 2017). A cave with natural openings offers direct access to the subsurface without drilling and deeper penetration into subsurface materials than could be obtained from a rover, landed platform, or penetrator launched from orbit. However, current technological and mechanical limitations associated with ingress and navigation make their exploration challenging. Caves form through a number of processes, but those on the moon and Mars identified using satellite data are lava caves. On Earth, lava caves are associated with basaltic lava, a material predicted to be ubiquitous on all rocky planets. On the moon and Mars, hundreds of vertical collapse pits have been identified using a number of remote sensing approaches (Greeley, 1971; Cushing et al., 2007; Haruyama et al., 2009; 2017); many of these may be skylights providing direct access to intact caves that should be substantially larger than those found on Earth due to the combination of lower gravity and higher eruption rates on these smaller planetary bodies (e.g., Blair et al., 2017). Future planetary astrobiology missions would be well-served to include lava caves as a high-priority target for investigation. The purpose of this white paper is to urge support for development of technology needed to enter a planetary cave with a scientific payload for deployment. In the next pages, we review the main challenges associated with: 1) identification of planetary lava caves, 2) subsurface exploration vehicles with advanced subsurface communications/operations techniques, and 3) sensor systems developed for biosignature identification. NASA's SMD currently supports several Earth-based planetary cave analog investigations through its PSTAR (Planetary Science and Technology through Astrobiology Research) program; a table summary of these efforts is also included. We conclude with mention of current and ongoing technology developments both internal and external to NASA that could advance planetary cave identification, access, and exploration.
Choosing optimal dam sites is a very complicated task due to the nature of karst and the insecurity of water storage often resulting in leakage from reservoirs. An appropriate project concept prior to exploration can significantly reduce the risks of water losses or at least minimize them to acceptable levels, while the absence or reduction of exploratory works can increase them. Many analyses show that once the reservoir is filled up, groundwater flow currently oriented toward the future reservoir would saturate the upper part of the karstified rocks, reactivate currently unsaturated (fossilized conduits) pathways, and form a reverse discharge outside of the reservoir area. The geological, hydrogeological, speleological, and other special investigation procedures should be permanent activities during the design stage, during the construction of the dam site and filling of the reservoir, as well as during exploitation. Having a good map, database, models, and geological, hydrogeological, and other 2D and 3D layers increases the chances of choosing a successful dam site and minimizes the possibilities of further leakage from reservoirs below the dam site and through the reservoir and dam site embankment. This chapter summarizes the necessary procedures for the acquisition of some of the basic information for choosing an optimal dam site and preventing leakage from reservoirs in karst formations through chosen characteristic examples. Several case studies involving mineral ore extraction and mine drainage in a karst aquifer environment are presented in this section. Mining operations often entail extremely high rates of groundwater inflow, which is a threat to safe mining. Insufficient knowledge about the hydrogeological setting and a lack of preventative drainage often lead to sudden inrushes. In the past, this has caused rapid mine flooding, material losses, and even human casualties. In the case of evaporite karst, ground subsidence resulting from rather fast dissolution of evaporite rocks is a special problem. The practical experience discussed in the section shows that various measures are undertaken to drain mining operations (including drainage wells on the ground surface, underground dewatering boreholes, drainage galleries, drainage shafts, and the like), as well as that grouting of karst conduits and caverns has not always been effective. The quality of karst groundwater, before it enters the zone of mining operations, is generally good. However, after the groundwater comes into contact with ore deposits, this quality frequently deteriorates. Numerous examples show that karst groundwater, when abstracted before it reaches mining operations, can be used for drinking water supply, irrigation water supply, and other similar purposes. The majority of karst terrains are characterized by a high degree of heterogeneity. The results obtained by applying methods for the assessment of local karstification (e.g., borehole tests) often cannot be reliable to extrapolate to a wider area. The use of remote sensing provides the opportunity to assess the spatial distribution of karstification in the subregional scale. Analysis of satellite and aerial images allows the identification of geomorphological and tectonic forms that may indicate the highly karstified zones. From the factors that indicate the karstification, and which can be mapped by remote sensing, two factors are selected: surface karstification (K
sf) and density of faults (T
f). By overlapping maps of these two factors using geographical information systems (GIS) techniques, the final map expressed through a KARST (karstification assessed by remote sensing techniques) index is obtained. For the first time, the mapping approach has been applied to the catchment area of Karuč springs (Montenegro). By surveying the catchment area after the preparation of the map of the KARST index, it was noted that the assessed degree of karstification by using remote sensing mainly matches to the field assessment of shallow karstification. The application of this approach provides an image of the spatial distribution of karstification, even for areas that are inaccessible for direct field research. The obtained map can be used as a basis for solving some of engineering problems in karst that are related to the regulation of water, extraction of groundwater, and protection of karst aquifers from contamination. The mixture of fresh groundwater and surface water is a frequent problem in karst, and most problematic for the sustainable use of fresh groundwater. This is mostly a result of a high permeability and low attenuation capacity of karst aquifers, particularly those formed in open (unconfined) structures. The problem becomes more complicated when karst aquifer is in contact with seawater and tapping coastal aquifers and distinguishing fresh from seawaters is regularly a very difficult task. For this purpose, the Phoenicians constructed special intake structures and still today, many attempts to address this problem are made and similar devices constructed. The regions in which a large number of submarine springs exist are the Mediterranean basin, Florida, the Caribbean basin, the Black Sea, the Persian Gulf, and the Pacific islands. The section includes an explanation of the classical Ghyben-Herzberg formula, which defines the relationship and interface between fresh and salty water, but also states that its application, as in the case of Darcy law, should be used with caution in the case of karst aquifers. Several chosen case studies from different locations (Yucatan Mexico, Libya, France, and Montenegro) provide an overview of problematic and very difficult management of littoral karstic aquifers. It is often the case that even implementation of sophisticated engineering works and controlled pumping of fresh groundwater cannot completely diminish salt water intrusion.
Atmosphere temperature propagates to under- ground in relation to thermal proprieties of rocks during the seasons. Although geological composition is the dominant factor on thermal exchange between underground and at- mosphere, the first meters of the surface are influenced by thermal phenomena in short temporal scale because of the low thermal conductivity of rocks. In this way, seasonal vari- ation of temperature weakly influences karst cavities, so that the inner temperature remains constant during the year (~ 14°-15°C).
During the winter, warmer air from the cavity produces a heat flux to the terrestrial surface where the atmosphere air is colder. These thermal fluxes are continuous while thermal gradient exists between underground and ground condition. The objective of this work is to test the infrared thermogra- phy as a method to reveal sinkholes, measuring the positive thermal anomaly that is produced at the surface point where heat flux from cavity goes up to the atmosphere. In particu- lar, field survey with an infrared thermocamera on six known and preset sinkholes in Salento Peninsula (in particular, in Avetrana, Leverano, Nardò and Salice Salentino town) are conducted for verifying the existence and the quantity of positive thermal anomaly during winter and clear-sky nights. The taken thermal images confirm that higher temperatures are measurable at the sinkholes if they join with the ground and they are not obstructed. These temperatures correspond to upward thermal fluxes that could originate between inner and outer of a cavity. In this way, we use infrared images for showing that it is possible to recognize cavities from the in- duced heat flux in.
This work shows the first data about the method for cavity access identification, but future research will be oriented to characterize the atmospheric and sinkholes condition (i.e. lithology, geometry, etc.) that induce the upward heat fluxes.
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.
The detection of underground structures, both natural and man-made, continues to be an important
requirement in both the military/intelligence and civil communities. There are estimates that as many as
70,000 abandoned mines/caves exist across the nation. These mines represent significant hazards to
public health and safety, and they are of concern to Government agencies at the local, state, and federal
levels. NASA is interested in the detection of caves on Mars and the Moon in anticipation of future
manned space missions. And, the military/ intelligence community is interested in detecting caves, mines,
and other underground structures that may be used to conceal the production of weapons of mass
destruction or to harbor insurgents or other persons of interest by the terrorists. Locating these
mines/caves scattered over millions of square miles is an enormous task, and limited resources necessitate
the development of an efficient and effective broad area search strategy using remote sensing
technologies. This paper describes an internally-funded research project of The Aerospace Corporation
(Aerospace) to assess the feasibility of using airborne hyperspectral data to detect abandoned cave/mine
entrances in a broad-area search application. In this research, we have demonstrated the potential utility of
using thermal contrast between the cave/mine entrance and the ambient environment as a discriminatory
signature. We have also demonstrated the use of a water vapor absorption line at12.55 μm and a quartz
absorption feature at 9.25 μm as discriminatory signatures. Further work is required to assess the broader
applicability of these signatures.
Habitat in lava tubes recently discovered on the Moon and Mars, should
become a unifying concept for occupancy. The first step is to obtain a
consensus from Agencies on the validity of the concept. Afterwards, two
types of research programs should be implemented: (1) Search for lava
tubes by dedicated polar orbiters carrying low frequency radar, thermal
IR imagers, and high resolution optics in the visible. Mapping,
classification and choice of site should be achieved before 2020. (2)
Development of specific technology to begin by the end of the 2020's: -
bulldozers, elevators, and cranes for access - inflatable cylindrical
structures of large dimension for housing.
Monitoring cave environments is important for several reasons. For instance, through the studies of cave environments, we can better protect cave ecology. Past experiments have monitored cave environments, although most of those were based on individual sensor nodes such as data loggers. In this paper we introduce and discuss a ZigBee wireless sensor network-based platform used for cave environment monitoring. The platform is based on a Freescale ZigBee evaluation kit. We carried out a proof-of-concept experiment in Junction Cave, a lava tube, at El Malpais National Monument in New Mexico. That experiment monitored temperature, humidity, and air turbulence inside the cave. The instrumentation consisted of a turbulence tower with five thermocouple-based sensors, reaching from the floor to the ceiling of the cave, temperature/humidity sensors distributed throughout the cave, and a low-power embedded Linux computer for data collection and storage. The experiment measured interesting air turbulence variations at different heights, which we related to to weather changes outside the cave and human activities inside the cave. The experiment also observed variations of air temperature at different locations inside the cave. In this presentation we will discuss the instrumentation as well as interpretations of the observations. The experiment demonstrated that a ZigBee wireless sensor network-based monitoring system is a potentially feasible platform for a cave environment monitoring system. We also found that network reliability, node cost, and power consumption need to be improved for future systems.
CratersoftheMoonNationalMonument(COM)basaltsofferareasonableanalogtomartianbasalts,asthey
haveelevatedironconcentrationscomparedtotraditional terrestrialanalogs.Althoughsecondarysulfate
mineralsontheevaporiticregionsofMarsconsistprimarilyofMg-,Ca-,andFe-bearingsulfateminerals,
recentorbiterspectroscopicdatahavesuggestedNa-sulfatemineralsmaybepresent.Secondarymineralsin
thebasalticcavesofCOMinsouthernIdahoarewhite,efflorescentdepositsinsmallcavitiesalongthecave
wallsandceilingsandlocalizedmoundsonthecave floors. ThesedepositswereexaminedusingX-ray
powderdiffraction(XRD),X-rayfluorescencespectrometry(XRF),Fouriertransforminfraredspectrometry
(FTIR),andlaserdesorptionFouriertransformioncyclotron massspectrometry(LD-FTICRMS).Thesecondary
mineralassemblagesweredominatedbyNa-sulfateminerals (thenardite,mirabilite)withasmallfractionof
thedepositscontainingminorconcentrationsofNa-carbonateminerals.Basedonthermodynamicmodeling
results,formationofthedepositswasattributedtoleachingofbasaltmineralsbymeteoriticwaterfollowed
by evaporationofsolutions.Suchdepositscouldform under similarconditionsinbasalticcavesonMars,
making cavesanexcellenttargetforastrobiologicalinvestigations.
The matched filter can be used to identify the location of a specific signal embedded in background correlated noise. The
maximum filter output indicates the likely location and, with appropriate statistical assumptions on the noise, it also serves
as a test statistic in the probabilistic evaluation of the filter’s performance. Different setups of the Neyman-Pearson statistical
hypothesis test yield predictions of either the probability of a miss or that of a false alarm. The needed statistics of the
maximum filter output are properly obtained using the distribution of order statistics. Through Monte Carlo simulations, we
analyzed the ability of the matched filter to identify a sub-surface anomaly in typically correlated gravity fields using
observations of elements of the gravity gradient tensor. We also evaluated the reliability of the hypothesis testing and the
associated predicted probabilities of misses and false alarms. Our simulations and statistical analyses confirm that the power
of the tests increases as the signal strength increases and as more gradient tensor components per observation point are included.
We also found that the hypothesis test that is designed to predict the probability of a miss is more robust and powerful than
the one for predicting a false alarm. Moreover, the probability of a miss is somewhat smaller than the probability of a false
alarm under otherwise equal circumstances.
Keywordsmatched filter–gravity gradients–hypothesis tests–probability of miss–probability of false alarm–power of test
Lava tubes and basaltic caves are common features in volcanic terrains on Earth. Lava tubes and cave-like features have also been identified on Mars based on orbital imagery and remote-sensing data. Caves are unique environments where both secondary mineral precipitation and microbial growth are enhanced by stable physico-chemical conditions. Thus, they represent excellent locations where traces of microbial life, or biosignatures, are formed and preserved in minerals. By analogy with terrestrial caves, caves on Mars may contain a record of secondary mineralization that would inform us on past aqueous activity. They may also represent the best locations to search for biosignatures. The study of caves on Earth can be used to test hypotheses and better understand biogeochemical processes, and the signatures that these processes leave in mineral deposits. Caves may also serve as test beds for the development of exploration strategies and novel technologies for future missions to Mars. Here we review recent evidence for the presence of caves or lava tubes on Mars, as well as the geomicrobiology of lava tubes and basaltic caves on Earth. We also propose future lines of investigation, including exploration strategies and relevant technologies.
Cave ecosystems are among the most fragile ecosystems on Earth (Elliott 2000; Hamilton-Smith and Eberhard 2000) due, in part, to the sensitivity of cave-dwelling organisms to disturbance. Because many troglomorphic taxa (obligate cave-dwelling organisms) are endemic to a single cave or region (Reddell 1994; Culver et al. 2000; Christman et al. 2005), and are generally characterized by low population numbers (Mitchell 1970; Krajick 2001), many populations are consid-ered imperiled (Reddell 1994; Culver et al. 2000). Most studies of cave invertebrates have been simple inventories, with relatively little data collected on species and commu-nity ecology. For this study we have synthesized all known information on cave-dwelling inver-tebrates in Grand Canyon National Park (GRCA). There is a paucity of knowledge about caves in GRCA, as well as other areas on the southern Colorado Plateau. The avail-able information is limited to a few intensive studies (where invertebrates were collected and identified) and cave trip reports (where invertebrates were documented visually). Here we determine the extent of knowledge concerning cave-dwelling invertebrate fauna, identify the seemingly most common cave-dwelling invertebrates, and present our preliminary understanding of invertebrate diversity and endemism in Grand Canyon caves. METHODS We conducted a literature review that in-cludes all published literature, obtained primarily through Northern Arizona Uni-versity's Cline Library and Internet searches, and unpublished literature and cave trip re-ports on file at GRCA Museum Collections. We did not include reports supported by little or no documentation or those in which invertebrate observations are not well described (i.e., above the family taxonomic level). We divided Grand Canyon cave inverte-brates into five cavernicole (cave-dwelling organism) groups and one special case cate-gory: (1) Troglobites, which are obligatory terrestrial cave-adapted species occurring only in caves or similar subterranean habi-tats, (2) troglophiles, which are species occurring facultatively within caves and completing their life cycles there, but prob-ably also occurring in surface environments, (3) trogloxenes, which are taxa that live in caves for shelter and potentially favorable microclimate but that return to epigean habitats to forage (refer to Barr 1968), (4) stygobites, which are obligatory aquatic cave-adapted organisms (refer to Culver and White 2005), (5) unknown cavernicoles, which are organisms not categorized due to a lack of information, and (6) special cases, which include organisms brought into the cave by vertebrate species. Additionally, be-cause organisms known to feed in guano deposits are of interest to cave ecologists, we included the subgroup guanophiles. Troglo-bites, troglophiles, and trogloxenes are the groups generally known to contain guano-philes. Current taxonomy was verified for most invertebrates using the Integrated Tax-onomic Information System (http://www .itis.gov) and Triplehorn and Johnson (2005).
Cave ecosystems are considered one of the most poorly studied and fragile systems on Earth. Belize
caves are no exception. This paper represents the first effort to synthesize information on both invertebrate
and vertebrate observations from a Belize cave. Based on limited field research and a review of literature,
we identified two ecologically sensitive areas, and developed a species inventory list containing
41 vertebrate and invertebrate morphospecies in Actun Chapat, Vaca Plateau, west-central Belize. Actun
Chapat contains two ecologically sensitive areas: (1) a large multiple species bat roost, and (2) a subterranean
pool containing troglobites and stygobites. The inventory list is a product of sporadic research
conducted between 1973 and 2001. Ecological research in this cave system remains incomplete. An
intensive systematic ecological survey of Actun Chapat with data collection over multiple seasons using
a suite of survey techniques will provide a more complete inventory list. To minimize human disturbance
to the ecologically sensitive areas, associated with ecotourism, we recommend limited to no access in the
areas identified as “sensitive.”
We analyzed temperature data of nine SW U.S. caves using Fourier
analysis to characterize thermal behavior, and line graphs to identify
optimal times of detection in the thermal infrared. This work furthered
our understanding of cave thermal behavior.
This study aims to increase our understanding of cave thermal behavior and to identify optimal times for detecting caves using thermal remote sensing. Techniques developed for Earth caves will ultimately be applied to locating subterranean cavities on the
Algorithms exploiting hyperspectral imagery for target detection have continually evolved to provide improved detection results. Adaptive matched filters can be used to locate spectral targets by modeling scene background as either structured (geometric) with a set of endmembers (basis vectors) or as unstructured (stochastic) with a covariance or correlation matrix. These matrices are often calculated using all available pixels in a data set. In unstructured background research, various techniques for improving upon scene-wide methods have been developed, each involving either the removal of target signatures from the background model or the segmentation of image data into spatial or spectral subsets. Each of these methods increase the detection signal-to-background ratio (SBR) and the multivariate normality (MVN) of the data from which background statistics are calculated, thus increasing separation between target and non-target species in the detection statistic and ultimately improving thresholded target detection results. Such techniques for improved background characterization are widely practiced but not well documented or compared. This paper provides a review and comparison of methods in target exclusion, spatial subsetting and spectral pre-clustering, and introduces a new technique which combines these methods. The analysis provides insight into the merit of employing unstructured background characterization techniques, as well as limitations for their practical application.
Discussion of the thermal conductivity of particulate materials is dispersed over several decades and a wide range of disciplines. In addition, there is some disparity among the reported values. This paper presents a review of the methodology available for the study of thermal conductivity of particulate materials, with an emphasis on low atmospheric pressures, and an assessment of the dependability of the data previously reported. Both steady state and nonsteady state methods of thermal conductivity measurement are reviewed, delineating the advantages, disadvantages, and sources of error for each. Nonsteady state methods generally are simpler and more efficient. The transient hot wire and differentiated line-heat source are the preferred methods for the laboratory. These methods are better suited for small samples and short measurement times and are therefore the best methods to use for a series of comprehensive studies. Results of previous studies are presented, compared, and evaluated. A good way to assess the relative accuracy is to compare the values of thermal conductivity versus atmospheric pressure obtained from several experimenters. The lowest values of thermal conductivity at vacuum and very low atmospheric pressure, and the steepest slopes on the thermal conductivity versus atmospheric pressure curves, are indicative of the most accurate data. Previous thermal conductivity studies have shown that the thermal conductivity of particulate materials increases with increasing atmospheric pressure, with increasing particle size, and with increasing bulk density of the material. At vacuum, the thermal conductivity of particulate materials is proportional to the cube of the temperature. The temperature dependence of thermal conductivity is much less obvious at higher atmospheric pressures.
A line-heat source apparatus was assembled for the purpose of measuring
thermal conductivities of particulate samples under low pressures of a
carbon dioxide atmosphere. The primary result of this project is the
compilation of the first comprehensive suite of measurements of the
dependence of thermal conductivity on particle size. The thermal
conductivity increases with increasing particle size and atmospheric
pressure. In particular, over the range of Martian atmospheric
pressures, from 1 to 7 torr, the thermal conductivity was found to be
empirically related to approximately the square root of the particle
diameter and the square of the cubed root of the atmospheric pressure.
At the average pressure of the Martian surface (6 torr) the thermal
conductivity varies from 0.011 W/mK, for particles less than 11 μm in
diameter, to 0.11 W/mK, for particles 900 μm in diameter. These
results differ significantly from the particle size dependence estimated
for Mars from previous measurements, except for 200-μm particles,
whose thermal conductivity is 0.053 W/mK. The thermal conductivities of
larger particles are lower than the previous estimate, by 40% at 900
μm, and the thermal conductivities of smaller particles are higher
than the previous estimate, by 60% at 11 μm. These newer estimates
agree with other lines of evidence from Martian atmospheric and
surficial processes and lead to improved particle size estimates for
most of the planet's surface.
Stejneger's 1896 description of Typhlomolge rathbuni, the Texas blind salamander, from the artesian well in San Marcos, inspired several important studies of the cave and phreatic fauna of the San Marcos area. Additional random collections in Texas resulted in the discovery of several additional troglobites and troglophiles of interest. No systematic survey of the cave fauna of the state, however, existed prior to the formation of the Texas Speleological Survey (TSS) in 1961. The TSS began an active program of collection in all caves visited, with several trips specifically designed to sample cave fauna. The early results of these studies were published by Reddell (1965, 1966, 1967,
Analyses of radon gas tracer measurements and observation of the variability of thermal structures have long been thought to indicate the presence of weak air currents in Niedzwiedzia (Bear) Cave, Kletno, Poland. However, only after ultrasonic anemometers were installed could different circulation systems of varying origin and the expected air movements be observed by direct measurement. This paper presents: a) the different methods applied in order to determine the weakest air currents both directly and indirectly; b) a summary of hypotheses on the subject; and c) the first results that air indeed moves in so- called static areas and that visitors affect both cave airflow and temperature. First results show that even in so-called static caves or within corresponding parts of cave systems, the term "static" has to be regarded as wrong with respect to the air currents as no situation where no air movements took place could be proven so far within the caves. Moreover, the influence of passing tourist groups on the cave climate could unequivocally be identified and demonstrated.
From the perspective of energy expenditure, ice is the most economical water resource to target for exploration on Mars. Theoretical stability criteria indicate the planetary-scale potential for ground ice poleward of about 40° latitude. Geologic indicators can constrain the exploration. Particularly useful in this regard are fluidized ejecta blankets, periglacial features, and relict glacial landforms. The relationship of such geomorphological indicators to the modern water resources is dictated by the processes responsible for water cycling in the Martian past and the extension of those processes to the present. The geomorphological evidence indicates extensive water cycling in the geologic past. Exploration strategies can develop around the resource potential of hydrated minerals, hydrothermal systems, and ground ice based on an evolving practical experience as resources are discovered.
Karst is a specific type of terrain (or landscapes) with characteristic suites of well-known surface and subsurface dissolutional features. The latter result from integrated subsurface drainage. A variety of nondissolutional processes forms terrains analogous to certain types of karst; these are termed pseudokarst. Before 1906, these generally were believed to be karst somehow formed in poorly soluble rocks. They share a considerable range of features, resources and values with karst, commonly (but not invariably) including eaves, and the two are linked across a wide spectrum of processes and features (e.g., between dissolutional and piping caves). Unlike karst, integrated subsurface drainage may not be present. Isolated caves define neither karst nor pseudokarst. Multiprocess terrains and landscapes are not uncommon. Based largely on conclusions of a working session of the 1997 International Congress of Speleology, eight types of pseudokarst are identified, with notably different implications for extraterrestrial habitats: rheogenic pseudokarst, glacier pseudokarst, badlands and piping pseudokarst, permafrost pseudokarst, talus pseudokarst, crevice pseudokarst, compaction pseudokarst and consequent pseudokarst. Some appear to exist on Mars. Speleologists expert in their differentiation should serve as consultants to planetary geologists.
Recently, hundreds of specimens of Mississippian vertebrates, both fish and (mostly) tetrapods, have been collected from a sinkhole near the town of Delta, southeastern Iowa. The most significant fish material appears to be a nearly complete lungfish (Tranodis sp.), and numerous individual bones and partly articulated fragments of a rhizodont crossopterygian. Two groups of "labyrinthodont' amphibians are known from excellent material: a colosteid temnospondyl and a "protoanthracosaur'. Although preparation and study of the Delta fauna are still at an early stage, features of the protoanthracosaur have already supplied important new information about early tetrapods, and have raised unexpected questions regarding the evolution of the tetrapod vertebral centrum. -from Author
The importance of natural ventilation at Yucca mountains is discussed. The geohydrologic system of the mountain is favorable for a passive ventilation system similar to the naturally occuring one at Kartchner Caverns. The natural ventilation can enhance the effectiveness of a geologic repository in isolating radioactive waste. A cross drift was constructed through the proposed repository block. This drift has been bulkheaded at three places to simulate the final closure and sealing of the proposed repository.
Airborne infrared thermal scanners can be used to detect crevasses and cave openings, but only under certain conditions. First, the temperature inside the void must be significantly different from external conditions; and second, some mechanism must exist to bring this thermal difference to the surface where it can be detected by a scanner. It must be determined if other events influence this mechanism. In the case of crevasses, conduction and convection both play a role in altering the surface temperature of the snow bridge over a crevasse. For caves, convection is the mechanism that brings about the temperature alteration. Convection is linked to the breathing cycle which, in turn, is caused by changes in atmospheric pressure. From ground measurements of internal temperature, external temperature, and atmospheric pressure a flight time can be picked that will provide the most favorable circumstances. Results are given for a crevasse field in Greenland and for a cave system in Puerto Rico.
Obligatory cavernicoles, or troglobites, have traditionally been of special interest to evolutionary biologists for several reasons. The existence of animal life in caves and other subterranean spaces at first attracted attention because of its novelty; intensive biological exploration of caves began little more than a century ago. Although the discovery and description of the cave faunas of the world is far from complete, especially in the Western Hemisphere, so much descriptive information has been compiled that we can safely assert that, at least in unglaciated, temperate parts of the world, the occurrence of numerous species of troglobites in any major limestone region is a common and highly probable phenomenon.
Karst is a specific type of terrain (or landscapes) with characteristic suites of well-known surface and subsurface dissolutional features. The latter result from integrated subsurface drainage. A variety of nondissolutional processes forms terrains analogous to certain types of karst; these are termed pseudokarst. Before 1906, these generally were believed to be karst somehow formed in poorly soluble rocks. They share a considerable range of features, resources and values with karst, commonly (but not invariably) including caves, and the two are linked across a wide spectrum of processes and features (e.g., between dissolutional and piping caves). Unlike karst, integrated subsurface drainage may not be present. Isolated caves define neither karst nor pseudokarst. Multiprocess terrains and landscapes are not uncommon. Based largely on conclusions of a working session of the 1997 International Congress of Speleology, eight types of pseudokarst are identified, with notably different implications for extraterrestrial habitats: rheogenic pseudokarst, glacier pseudokarst, badlands and piping pseudokarst, permafrost pseudokarst, talus pseudokarst, crevice pseudokarst, compaction pseudokarst and consequent pseudokarst. Some appear to exist on Mars. Speleologists expert in their differentiation should serve as consultants to planetary geologists.
Early in its history, Mars underwent fluvial erosion that has been interpreted as evidence for a warmer, wetter climate. However, no atmosphere composed of only CO2 and H2O appears capable of producing mean planetary temperatures even close to 0 degrees C. Rather than by precipitation, aquifer recharge and ground water seepage may have been enabled by hydrothermal convection driven by geothermal heat and heat associated with impacts. Some climatic warming was probably necessary to allow water to flow for long distances across the surface. Modest warming could be provided by even a low-pressure CO2 atmosphere if it was supplemented with small amounts of CH4, NH3, or SO2. Episodic excursions to high obliquities may also have raised temperatures over some portions of the planet's surface.
This impressive hard backed tome, built from 250-year-life paper ... brings to mind ... Bert Leston Taylor's poem, lauding the mighty dinosaur, which is 'Famous ... not only for his power and strength, But for his intellectual length.'
[This article is not currently on open access however page 237 appears to be freely available via this link: https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2451.2004.00480.x]
The deep cave zone, to which the obligatory species are restricted, is perpetually dark, nearly isothermal, has a nearly constantly saturated atmosphere possibly above the limits of most terrestrial arthropods, and usually an apparent food-limited ecosystem. I postulate that in adapting to exploit the rigorous cave environment, terrestrial troglobites have had to cope with a water surplus and have become more like aquatic organisms in their water balance mechanisms. This hypothesis is corroborated by the general observation that the drying power of the cave environment is an important parameter in understanding the distribution of terrestrial troglobites. Three main physical factors all tend to create a drier and less stable cave environment in the tropics and reduce the proportion of colonizable area in tropical caves for terrestrial troglobites. These factors are (1) tropical caves are warmer and the rate of evaporation rises almost exponentially with temperature; (2) in the tropical regions the night-time temperature usually falls below the average annual temperature, so that for tropical caves nearly every night is a winter in terms of water vapor exchange; and (3) the higher solution and erosion rates in tropical caves create more entrances, larger passages, and raised relief, allowing more air communication with the surface. These factors do not preclude the existence of terrestrial troglobites in the tropics, but caves in the tropics that meet the requirements of an adequate moisture supply and a stable environment are more difficult to find and to survey In fact, the bioclimatic model predicts that many more troglobites will be discovered as more tropical caves are surveyed and also predicts that they will be found only in cave passages that have a stable saturated or nearly saturated atmosphere.
After decades of speculation and fruitless searches by observers, the lunar atmosphere was first observed by Apollo surface and orbital instruments beginning in 1971. With the end of Apollo missions in 1972 and the termination of funding for Apollo lunar ground station observations in 1977 the field withered for many years, but it has recently enjoyed a renaissance. This renewal was initiated by the discovery of lunar atmospheric sodium and potassium by ground-based observers and was furthered by the in situ detection of metal ions derived from the Moon in interplanetary space, the possible discoveries of H2O ice at the poles of the Moon and Mercury, and the detection of tenuous atmospheres around other remote sites in the solar system, including Mercury and several Galilean satellites. In this review I attempt to summarize the present state of knowledge about the lunar atmosphere, describe the important physical processes taking place within it, and compare the lunar atmosphere with other tenuous atmospheres in the solar system.
A Radar Flashbulb on the Moon: Lava-tube caves under the lunar surface may be very useful as lunar base sites. They have left surface indicators that can be found in computerized searches of the Clementine data. Such a search is being put together by the Lunar Base Research Team (LBRT) of the Oregon L-5 Society, Portland's local chapter of the National Space Society. Lava-tube sites that are located will need to undergo further investigation before committment to a lunar base can be made. Ground-penetrating radar images of actual voids at particular sites would seem to be the next step, if images can be obtained cheaply. This paper describes what LBRT believes is the cheapest combination of technologies that can obtain such images of lava-tube voids on the Moon. As early as the Apollo Lunar Sounder Experiment, radar has penetrated the Moon to substantial depths. Only soundings were possible, given the combination of penetrating wavelengths (1-20 m) and the aperture of any antenna that could be carried by the Apollo Service Module. Now, operation of the Very Long Baseline Array (VLBA) by NRAO provides an aperture that, even from the Earth, could provide a resolution of 25-50 m at the lunar surface with wavelengths of 0.5-1 m. The Lunar Sourcebook notes that much of the lunar surface is rather transparent to radio waves, because of its low conductivity and lack of water. Lava-tube surface indicators have been found in Apollo photos for caves up to 1100 m across. But where is the radar energy reflecting off the walls of these lava-tube voids to come from?
Consideration of the effects of gravity on lithostatic stress on Mars indicates that dilational faulting found in the upper 2 km on Earth may extend to depths of 5 km on Mars.
The mid-Tertiary Pacencia Group comprises over 2km of continental sediments. It was deposited in a half-graben basin thought to have been active since early Tertiary times. Conglomerates along the western basin margin were deposited as longitudinal bars, rare transverse bars and channel fills. To the east, a succession was deposited in playa sub-environments. Lakes existed at various stages and were fed by permanent fluvial systems. The playa sediment were derived from crystalline source areas to the east. Proximal fan facies and sediment sources are now buried under the volcanic Andes.-from Author
The Salar de Atacama in northern Chile accumulated halite during the Pliocene and Quaternary under conditions that alternated between a saline lake and a dry salt flat. Hidden beneath its uninterrupted flat surface is the Salar fault system. The halite deposits provide a high-resolution history of deformation. Contours on the ca. 5 Ma base of the halite unit in the southern salar, defined in a deep oil-exploration borehole and traced through reflection seismic lines, reveal that net reverse offset across the Salar fault system is down-to-the-east by ∼900 m; of that total, 200 m occurred during the Quaternary and 700 m during the Pliocene. Distributions, thicknesses, and geometries of eight stratigraphic sequences within the halite unit reveal a history of episodic faulting and demonstrate that faulting during approximately half the 5 m.y. interval, including the Holocene, did not generate fault scarps. We suggest that deposition caused by evaporation of ground water brines in the salt flat, rather than either dissolution or deflation, has smoothed the topography of the dry lake bed across the active fault zone. For the case of west-directed groundwater flow, we propose that the east-facing Salar fault system focuses groundwater flux along the eastern flank of the fault, which enhances halite precipitation in the down-thrown block during desiccated stages and counteracts fault-driven topographic relief. The realization that a seismic risk may exist even though the Salar fault system is hidden leads to the appreciation that leads to the appreciaton that similar unrecognized seismic risk may exist in more populous aric basins.
We assembled a list of obligate cave-dwelling species and subspecies, their county distribution, and their provisional global conservation rank. A total of 927 species and 46 additional subspecies in 96 families exclusively from cave and associated subterranean habitats have been described in the 48 contiguous states of the United States. The terrestrial (troglobitic) species are concentrated in northeast Alabama (especially Jackson County), with other concentrations in Kentucky, Texas, Virginia, and West Virginia. Only 23 counties, comprising less than 1% of the land area of the 48 contiguous states, account for over 50% of the terrestrial species and subspecies. The aquatic (stygobitic) species are concentrated in Hays County, Texas, with other concentrations in Florida, Oklahoma, Texas, Virginia, and West Virginia. Only 18 counties, comprising less than 1% of the land area, account for over 50% of the aquatic species and subspecies. Endemism is high, with 54% of the species known from a single county. Approximately 95% of the species are listed by The Nature Conservancy as vulnerable or imperiled in the United States. These cave species comprise 50% of all vulnerable or imperiled species listed in databases of the Natural Heritage Program. Less than 4% of these subterranean species have federal status. Conservation can best be accomplished through habitat protection, which must include protection of the associated surface habitat.
Mixed pixels occur commonly in remotely-sensed imagery, especially those with a coarse spatial resolution. They are a problem in land-cover mapping applications since image classification routines assume ‘pure’ or homogeneous pixels. By unmixing a pixel into its component parts it is possible to enableinter alia more accurate estimation of the areal extent of different land cover classes. In this paper two approaches to estimating sub-pixel land cover composition are investigated. One is a linear mixture model the other is a regression model based on fuzzy membership functions. For both approaches significant correlation coefficients, all >0·7, between the actual and predicted proportion of a land cover type within a pixel were obtained. Additionally a case study is presented in which the accuracy of the estimation of tropical forest extent is increased significantly through the use of sub-pixel estimates of land-cover composition rather than a conventional image classification.
An artificial neural network based on the multilayer-perceptron model has been used to classify two-date multispectral SPOT High Resolution Visible (HRV) imagery on a test site in the Departement Ardeche, France. A large network consisting of 98 nodes was trained successfully to classify 20 land-cover classes. A ground dataset comprising 1881 pixels was used to verify the accuracy of the classifier. The average accuracy achieved over all classes in the verification dataset was 81 per cent, exceeding the performance of a maximum-likelihood classifier by 28 per cent.
The Viking mission has profoundly influenced scientific thinking about the question of life on Mars. Based on the restfits obtained from a number of Viking investigations, it is clear that the surface of the planet is too hostile to support a carbon-based biota. While the existence of biological "oases" elsewhere on the planet have been proposed, none have yet been found. Other information based on Viking data has focused on the possibility that life may have been present on Mars in the distant past, and Viking images have revealed sites on Mars where further exploratory studies for extinct biology are warranted. From the point of view of the search for life on Mars, there is little doubt that the Viking mission, while it did not completely settle the question of life on Mars, put to rest a number of predictions and speculations about this issue. At the same time, new insights derived as a consequence of this mission have resulted in radical revisions in scientific thinking about the possibility of life on Mars. For one thing, up until the Viking mission (and, indeed, also assumed in that undertaking) there was the implicit belief that, if there was life on Mars, it would be confined to the surface and near-surface regions of the planet. By analogy with biology on the Earth, it was reasonable to assume that photosynthetic orgardsms would play a prominent role in any Mars ecological system, and thus require access to solar energy. The data obtained by Viking are best interpreted as indicative of the fact that the surface on Mars is hostile to life and devoid of life.