Aircraftused for thermal imagery acquisition missions, April 2011. Taking off from Edwards Air Force Base, Mojave Desert, California. Courtesy NASA Armstrong Flight Research Center.
Background
Planetary caves have been found on nearly every planetary body in our Solar System. More than 200 cave-like features are known from the Moon and over 1000 have been identified on Mars. Features that may lead to deep subterranean interiors have also been recorded on Titan, Triton, Europa, Enceladus, Ganymede, Io, Vesta, Venus, Ceres, Pluto, and even on comets.
On the Moon and Mars, caves will be vitally important for future robotic exploration and human habitation. Lunar caves not only offer among the best places to establish astronaut shelters, but could also serve as a test bed for advancing robotic techniques for planetary applications. For Mars, if life existed or exists, one of the best locations to search for evidence will be underground. Caves offer protection from low surface temperatures, unfiltered ultraviolet radiation, and violent windstorms, which may degrade and decompose organic materials. Importantly, Martian caves may also contain stable water ice. A manned mission to Mars will require water for human consumption, as well as conversion to oxygen for human consumption and liquid hydrogen for fuel. If water ice deposits exist and we can access to them, this would reduce some of the risk associated with a human mission to the red planet. Finally, because the harsh surface conditions, NASA may desire to build temporary or permanent astronaut (or speleonaut) bases underground. By their nature, caves contain a natural protective rock cover that can provide a level of protection not afforded by surface habitation pods.
Global Mars. Map overlay of the 1,032 identified cave locations (red and yellow dots; from Cushing 2016) with a geospatial model predicting regions of subterraneanstable water ice (highestaccumulationvalues in red; Williams et al. 2010).From Wynne et al. (2020).
The Search for Caves on Mars
Courtesy NASA Armstrong Flight Research Center and NASA TV.
With Dr. Murzy Jhabvala, NASA Goddard, examining thermal imagery captured during field experiments in the Mojave Desert, California. Courtesy Glen Cushing.
Since 2005, Jut has been involved in several projects to advance detection capabilities of caves on Earth and other planetary bodies. Initially, this work was centered upon developing techniques to find terrestrial caves using thermal remote sensing imagery and then applying this approach to search for caves on Mars. This work resulted in finding the earliest evidence of cave-like features on Mars. By studying the salt caves in the Atacama Desert of northern Chile, the deep vertical volcanic pits on the Big Island, Hawaii, and lava tube caves in the Mojave Desert of Southern California, Jut and others improved the understanding of cave thermal behavior and the detection of caves. In the Atacama Desert, Jut and his fellow researchers examined how surface temperatures influence cave temperatures, while on the Big Island, they studied how the sun differentially warms the interior walls of deep volcanic pits. In Mojave Desert, several experiments were conducted to advance the capabilities of the QWIP thermal imaging instrument developed by NASA Goddard engineers. Part of this work included an airborne imagery acquisition mission conducted in 2011.
Since these studies, their work has been evolved into developing strategies to help usher in an era of planetary caves’ exploration including the development of a mission concepts for robotic exploration of a Martian cave.
Contributions
On the pre-dawn thermal imagery collectionmission over the Mojave Desert, California.Courtesy NASA Armstrong Flight Research Center.
To date, Jut and colleagues have published over two dozen papers related to planetary caves. Recently, they provided recommendations to the National Academy of Sciences for the 2023 Decadal Survey for Planetary Science and Astrobiology. They submitted two white papers — one paper identified robotic and human exploration needs for planetary caves (that should be addressed over the next ten years), while the second proposed a mission concept for a robotic mission to a Martian cave.
Additional contributions to planetary caves science includes the following.
Demonstrated the viability of using terrain analysis algorithms on thermal imagery: By analyzing the 2011 thermal imagery collected in the Mojave Desert, Jut and colleagues applied a statistical framework to evaluate the utility of algorithms routinely used for the study of elevation models. Using these terrain layers, they found a number of unrecorded cave entrances.
Validated the importance of capturing and analyzing multiple thermal images for terrestrial cave detection: A luxury rarely afforded from planetary mission data, the use of multiple images acquired at the hottest time of day (early afternoon) and the coldest time of day (dawn) captures the variability of thermal behaviors of the entrance and surface. These data can be used in a statistical framework to best differentiate cave entrances from non-cave anomalies.
Planetary caves architecture recommendations for the next ten years. From Titus et al. (2020).
Estimated cave roof thickness using thermal conduction modeling: Using a series of ground-based temperature placed on the surface and within a cave, the team accurately calculated the thickness of a cave roof (overburden) by analyzing hourly temperature data collected from the surface temperature and cave deep zone.
Developed a novel technique to manually 3D map caves: Jut and others pioneered this technique in the Atacama Desert and later applied it for mapping caves in the Mojave Desert.
Identified the first cave-like features on Mars: Led by Glen Cushing, Jut and others published a paper describing seven deep vertical pits (aka the ‘Seven Sisters’) on the northern flank of Arsia Mons, Mars.
Characterized thermal behavior and identified detection times: Using ground-based measurements and statistical modeling, the best times to detect two Atacama Desert caves were identified. Pre-dawn and high noon conditions were optimal in the Atacama, and were also optimal detection times for Mojave Desert caves.
While not a scientific contribution per se, Jut’s involvement with field testing LEMUR (the world’s first rock climbing robot) in the Mojave Desert earned him a footnote — he’s the first human to belay a robot. For the most up to date information on LEMUR, go here.
Colonizing the Caves of Mars
Courtesy Chicago Ideas Week.
Further Reading
The 2010 expedition team, from left to right, Tim Titus, Dan Loewen, Peter Shu, Murzy Jhabvala, and Jut, Mojave Desert, California.
