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Mars Astrobiological Cave and Internal habitability Explorer (MACIE): A New Frontiers Mission Concept

Mars Astrobiological Cave and Internal habitability Explorer (MACIE):
A New Frontiers Mission Concept
By: C. Phillips-Lander (, A. Agha-mohamamdi2, J. J. Wynne3, T. N. Titus4,
N. Chanover5, C. Demirel-Floyd6, K. Uckert2, K. Williams4, D. Wyrick1, J.G. Blank7,8, P. Boston8, K.
Mitchell2, A. Kereszturi9, J. Martin-Torres10,11, S. Shkolyar12, N. Bardabelias13, S. Datta14, K.
Retherford1, Lydia Sam11, A. Bahardwaj11, A. Fairén15,16, D. Flannery17, R. Wiens17
1Southwest Research Institute
2 NASA Jet Propulsion Laboratory
3Northern Arizona University
4U.S. Geological Survey
5New Mexico State University
6University of Oklahoma
7Blue Marble Space Institute of Science
8NASA Ames Research Center
9Konkoly Thege Miklos Astronomical Institute, Budapest, Hungary
10Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Spain
11University of Aberdeen, United Kingdom
12USRA/NASA Goddard
13University of Arizona
14University of Texas-San Antonio
15Centro de Astrobiogía, Spain
16Cornell University
17Queensland University for Technology, Australia
18Los Alamos National Laboratory
Mission Concept for Mars Subsurface Life and Habitability
1. Martian lava tubes are one of the best places to search for evidence of life
The Mars Astrobiological Cave and Internal habitability Explorer (MACIE) mission concept is named
for Macie Roberts, one of NASA’s ‘human computers’ (Conway 2007). MACIE would access the
Martian subsurface via a lava tube. Lava tube caves are compelling subsurface astrobiological targets
because they have their own relatively stable microclimates, are shielded from radiation and harsh
surface conditions, and may contain water ice (Blank et al., 2020). They may also provide access to
materials vital to future human exploration and in situ resource utilization (ISRU) activities (Sam et
al., 2020). A cave mission represents a compelling next-step in Mars astrobiology and
habitability exploration, because it would examine the deeper subsurface (>20x deeper than
prior surface craft) without the cost and risk associated with a deep drilling payload.
Subsurface Mars among the best places to look for post-Noachian habitable environments
Post-Noachian Mars (<3.1 Ga) near-surface habitability rapidly degraded, making near-surface
environments inhospitable to life as we know it. Organics observed on Mars to date are oxidized due
to radiation making it challenging to search for unambiguous biosignatures in near-surface
environments (Eigenbrode et al., 2018). Additionally, transient liquid brines may form at the surface,
but may not persist long enough to be habitable (Rivera-Valentin et al., 2020). In contrast, modelling
of subsurface environments indicates metastable water ice (Williams et al., 2010) and brines (Burt and
Knauth, 2003) may be present over extended time periods and have chemical disequilibria necessary
to support life. Thus, subterranean Mars may be the best place to look for habitable
environments and evidence of life. NASEM’s Astrobiology Strategy (2019) recommends
targeting the Martian subsurface habitability, which has yet to be the focus of a planetary
Tharsis lava tubes may have been habitable in the Amazonian
Hundreds of lava tube entrances are located within Hesperian–Amazonian terranes in the Tharsis
region (Cushing et al., 2015) and are expected to host metastable water ice (Williams et al., 2010).
Mapping of the Tharsis region demonstrates both glacio-volcanism (Cassinelli and Head, 2019) and
hydrothermal fluvial activity (Hargitai and Guilick, 2018), which may have occurred into the late
Amazonian. This suggests hydrothermal fluid fluxes from the surface to the subsurface may have
occurred as they do in modern volcanic systems, as well as melting of glaciers associated with glacio-
volcanic activity, similar to Iceland. The Tharsis region also hosts vast fracture networks, which would
provide means to transport surface waters and nutrients into the subsurface (Bouley et al., 2018). Thus,
lava tube caves may represent a modern and/or recently habitable environment on Mars.
Detection of habitable conditions in the subsurface of Amazonian Mars would fundamentally
change our view of Mars’ habitability and astrobiological potential through geologic time.
2. MACIE will determine the Habitability and Astrobiological Potential of a lava tube cave
MACIE focuses on two key questions: (1) how long were habitable conditions maintained within a
Martian cave? and 2) did life ever colonize a Martian cave? These questions are translated into two
primary goals: 1) assess the present and past habitability of a Martian lava tube and (2) search for
evidence of past or present life in a Martian lava tube. MACIE would address multiple goals of
Summary of Key Points
1. Martian subsurface habitability and astrobiology can be evaluated via a lava tube cave, without drilling.
2. MACIE addresses two key goals of the Decadal Survey (2013-2022) and three MEPAG goals.
3. New advances in robotic architectures, autonomous navigation, target sample selection, and analysis will
enable MACIE to explore the Martian subsurface.
Mission Concept for Mars Subsurface Life and Habitability
NASA’s Strategic Plan (2020), Planetary Decadal Survey (2013-2022), NASEM’s Astrobiology
Strategy (2019), and MEPAG goals (Bandfield et al., 2020) (Table 1: Science Traceability
Matrix; STM). MACIE may yield bonus science including insight into future human exploration
(MEPAG Goal 4).
Goal 1: Assess the present and past habitability of a Martian lava tube
Understanding the present and past habitability of a lava tube will be essential in providing the context
for evidence of life and/or life-related processes if they are observed. If no evidence of present or past
life is detected, the habitability assessment would help explain why evidence of life was not observed.
MACIE’s habitability assessment addresses the Planetary Decadal Survey Goals 4 and 5, NASEM’s
Astrobiology Strategy (2019), and multiple MEPAG Goals.
Objective 1A Determine whether brines or water ice are present: Water is essential to habitability of
environments as we know them. MACIE would quantify and characterize the distribution of liquid
brines and water ice that may be present in the cave using Raman and visible and infrared reflectance
(VISIR) spectroscopy and a camera with appropriate lighting. MACIE would also assess the thickness
of the overburden, temperature, and relative humidity along a transect within the cave using a
meteorological suite, which can aid in determining why brines or ice are or are not detected during
MACIE’s mission. Such an endeavor would also help to ascertain the structural integrity and
approachability of a particular lava tube or cave for sustained future human exploration. These
measurements address MEPAG Goal 2 “Assess the processes and climate of Mars” and Goal 4
“Prepare for human exploration.
Objective 1B Determine whether aqueous alteration occurred now or in the past: Evidence of water:rock
interaction will determine whether liquid water was present in the cave over geologic time. Using a
multispectral instrument, we would determine the presence of alteration minerals, including clays, Fe-
oxyhydroxides, sulfates, and other minerals indicative of aqueous alteration of the primary igneous
rock substrate. Using Raman and VISIR spectroscopy, MACIE is designed to assess the mineralogy
and chemistry of the cave ceilings, walls, and floors and enable MACIE to determine whether oxidant
rich dust has been transported from the surface. Martian dust, which contains salts (i.e. chlorides,
perchlorate, and sulfates), may influence the sublimation of ice and the development of brines, which
would influence the development of redox gradients and long-term maintenance of ice that could
support or sustain life. MACIE addresses “the spatial and temporal distribution of potentially
habitable environments…in the subsurface,” (NASEM, 2019) and MEPAG Goals 2 and 3).
Objective 1C Determine the presence of nutrients and chemical disequilibria necessary to support life: The
distribution and availability of CHNOPS+Fe elements in the solid phase has been shown to influence
microbial colonization in terrestrial lava tubes (Popa et al., 2012; Phillips-Lander et al., 2020). Nutrients
required for life are accessible from both the aqueous (condensation, liquid water) and solid phases
(rocks, minerals, and water ice). A camer paired with Raman and laser-induced breakdown
spectroscopy (LIBS) will identify and quantify the chemistry of ices, primary rock substrates, and
alteration phases to determine the availability of nutrients and energy, in the form of chemical
disequilibria, available within the cave to promote and sustain life in the absence of light (NASEM,
2019; MEPAG Goal 3).
Objective 1D Radiation Flux in the Subsurface: While some microorganisms survive exposure to high
radiation levels (Battista, 1997), many microorganisms cannot. Cave roof thickness determines
whether the radiation environment is within the cave. We anticipate cosmic rays and neutrons will
penetrate a Martian cave with an overburden up to 500 g cm2 (~3 m; Turner and Kunkel, 2017).
Quantifying radiation levels using a radiation sensor would serve to explain microbial habitat suitability
(MEPAG Goal 1).
Table 1: MACIE Science Traceability Matrix
Goal Science Objective Physical Parameters Observables with Uncertainty Instrument Closure/Benefit
1A.1 Determine whether the destination
cave atmosphere is consistent with the
metastability of water ice (e.g. Williams
et al., 2010)
1A.2 Determine whether evidence is
consistent with the presence of brine or
water ice in the destination cave (Hargitai
and Guilick, 2018; Williams et al., 2010)
1A. Determine whether
habitable conditions have
ever existed within the
candidate Martian lava tube
as quantified by the
presence of water.
1. Assess the present and past habitability of the destination lava tube cave.
1B.1 Determine whether evidence
indicative of past liquid water or water ice
exists in the destination cave as evidenced
by aqueous alteration
1C.1 Determine whether evidence
indicative of nutrients and energy
necessary to support life are present in the
destination cave.
2A.1 Determine whether the destination
cave contains biomolecular compounds,
consistent with the presence of
carbon-based life.
2A.2 Determine whether the destination
cave contains mineral chemistry consistent
with bioalteration
2B.1 Determine whether the destination
cave contains morphological features
consistent with biosignatures of life
1B. Determine whether
habitable conditions have
ever existed within the
candidate Martian lava tube
as quantified by evidence of
aqueous alteration
2A. Determine whether the
candidate lava tube
contains evidence
consistent with the
presence and activity of
extant or past life
2.Search for evidence of
present or past life in the
desitnation lava tube cave
Decadal Survey (2013-2022) Planetary Habitats Priority QuestionsMEPAG GOALS National Academies Astrobiology
Strategy (NASEM, 2019) “4. Did Mars [...] host ancient aqueous environments conducive to early life, and
is there evidence that life emerged?
5. Are there contemporary habitats with the necessary conditions, organic matter,
water, energy, and nutrients to sustain life, and do organisms live there now?”
“What is the spatial and temporal distribution of
potentially habitable environments on Mars,
especially in the subsurface?”
1. Determine if Mars ever supported life;
2.Understand the processes and climate of
Mars; 3. Understand Mars as a geologic
system; and 4. Prepare for human explora-
Measure air and wall temperature (+/- 2oC); relative humidity
(+/- 5%); atmospheric pressure to (+/- 1 Pa) Environmental station
Raman, Microimaging
camera & Camera
Build climate models to understand the
factors (climate, environmental, and
geologic) influencing the metastability of
water ice (MEPAG Goal 2, 3). Bonus:
MEPAG Goal 4
Measure radiation levels (0.05 mSV/h) at different depths
within the cave to estimate overburden thickness to (+/-1 cm)
Quantify alteration minerals (+/- 5 wt% on a 10 cm scale) e.g.
clays, Fe-oxides, sulfates, etc. indicative of aqueous alteration
of the primary geologic substrate
Quantify mineral hydration states (+/- 5 wt% on a 10 cm scale)
e.g. clays, Fe-oxides, sulfates, perchlorate, etc.
Raman & VISIR
Quantify the spatial distribution of H2O (brines or solid phase
water) in the subsurface on cm-m scale.
Detect morphological biosignatures in the
subsurface (Decadal Survey Theme 1;
NASEM 2019; MEPAG Goal 1)
Map composition of primary substrate of the cave interior to
determine mineralogy (+/- 5 wt%) and elemental (+/-0.1 wt%)
Determine the distribution of nutrients (CHNOPS+Fe) (+/-0.1
Raman & VISIR
1D.1 Determine whether the destination
cave is significantly deep to attenuate
radiation flux to a level compatible with
terrestrial extreomphiles
Measure radiation levels (0.05 mSV/h) at different depths within
the cave to constrain the atmospheric exchange rate with the
1D. Determine whether
habitable conditions exist
within the candidate Martian
lava tube as quantified by
radiation attenuation
Determine the presence and identity of organic molecules (i.e.
amino acids, lipids, exopolymeric substances, etc) to 1 ppbv of
rock, dust, ice and/or water present in the candidate cave
Larger structures can be
resolved by a microimag-
ing camera (e.g > 60 μm)
Textural evidence including biovermiculations (spatial patterns
of organics and minerals), mineral size and shape (10 μm to
2.5 cm)
Map composition of alteration minerals within the cave,
particularly those spatially co-located with organics to
determine mineralogy (+/- 5 wt%) and elemental (+/-0.1 wt%)
Detect mineralogical biosignatures in the
subsurface (Decadal Survey Theme 1;
NASEM 2019; MEPAG Goal 1)
Detect organic biosignatures in the
subsurface (Decadal Survey Theme 1;
NASEM 2019; MEPAG Goal 1)
Understand the impact the radiation
environment has on habitability (Decadal
Theme 2; NASEM 2019; MEPAG Goal 3).
Bonus: MEPAG Goal 4
Understand nutrients, energy (redox)
available to support life (Decadal Theme
2; NASEM 2019; MEPAG Goal 3)
Understand the alteration history
(Decadal Theme 2; NASEM 2019;
MEPAG Goal 3)
Determine whether the subsurface
environment contains brines or water ice
(Decadal Theme 2; NASEM 2019;
MEPAG Goal 3). Bonus: MEPAG Goal 4
1C. Determine whether
habitable conditions ever
existed within the candidate
Martian lava tube evidence
of nutrients and chemical
Radiation sensor
Radiation sensor
fluorescence spectroscopy
Mineralogy: Raman &
VISIR spectroscopy;
Composition: LIBs
Mineralogy: Raman, VISIR
spectroscopy microimager;
Composition: LIBs
Map the cave in 3D to build a model of its volume and extent Camera
Mission Concept for Mars Subsurface Life and Habitability
Goal 2: Search for evidence of extant or past life in a Martian lava tube
MACIE is designed to target multiple objectives to determine whether life may have existed in a lava
tube now or in the past, including biomolecule components, minerals formed as byproducts of
metabolic activity, and biofabrics (Neveu et al., 2018). These biosignatures would indicate whether life
may have colonized a Martian cave and represent a major advance in our understanding of the
astrobiological potential of Mars’ deep subsurface. These measurements directly address Planetary
Decadal Survey Goals 4 and 5 and MEPAG Goal 1 “Determine if Mars ever supported life.”
Objective 2A Detection of biomolecular compounds consistent with carbon-based life: MACIE is designed
to measure the abundances of amino acids, carboxylic acids, lipids, proteins, DNA and RNA, and
other organic molecules which may be of biomolecular origin to assess the astrobiological potential
of the cave (Neveu et al., 2018) using time-resolved fluorescence spectroscopy.
Objective 2B Detection of textural evidence indicative of microbial activity: Microbial mat growth in
terrestrial caves can produce biovermiculation patterns, which are micro- to macroscopic deposits
resulting from the geochemical interactions of rich microbial colonies with their host rocks
environments (Jones et al., 2008). MACIE is designed to determine whether biofabrics exist in the
lava tube using a microimaging camera.
Objective 2C Presence of alteration products consistent with bioalteration: Oxide-hydroxide iron and
manganese mineral deposits, which are quickly precipitated through microbial redox reactions, can
also give rise to distinctive morphologies (Posth et al., 2014). Additionally, Si-rich iron hydroxides,
silicate-carbonate assemblages (Mg-rich clays with calcite and aragonite), and amorphous silica
layers/films on basalts in terrestrial lava caves are associated with microbial biofilms. These
compounds represent the types of chemical and mineralogical biosignatures that may have formed in
Martian caves (Léveillé et al., 2007; Miller et al., 2014). Presence of biominerals would be determined
with Raman, VISIR, and time resolved fluorescence spectroscopy.
3. MACIE Leverages Heritage Instrumentation to Achieve Science Goals
Recent in situ investigations of Mars, including
Mars Science Laboratory and Insight, include a
suite of instruments to characterize the
habitability, composition, and interior structure of
Access to samples may be limited; many
scientifically interesting samples may reside on
overhangs or walls. Therefore, MACIE’s instrument suite would conduct stand-off in situ
experiments, allowing the mission to pursue the most interesting habitability and
astrobiological targets. The baseline payload includes three instruments: a meteorological suite (e.g.
ExoMars 2022 HABIT), a multi-spectral instrument to assess chemistry and mineralogy and provide
hand lens quality microscopy (e.g. Mars2020 SuperCam), and a high-resolution context camera (e.g.
Mars2020 Mastcam-Z). Estimates for mass, power, and data are based on these heritage instruments
listed in Table 2. These instruments would address all science experiments in the STM (Table 1).
These instruments operate at high stand-off distances from science targets, and represent
recently flown, technically mature payloads for a Mars environment that would require limited
modifications for a planetary caves mission.
Meteorological suite
HAbitability: Brines, Irradiation and Temperature (HABIT) (Martín-Torres et al., 2020) measures
temperature, relative humidity, barometric pressure, wind, dust, and radiation; these data would be
Table 2: Proposed MACIE Instrument Suite
Mission Concept for Mars Subsurface Life and Habitability
incorporated into 2D and 3D cave climate models, explain the presence or absence of predicted water
ice, and determine the radiation environment (Science Objectives 1A and 1C; Table 1).
Multi-spectral Instrument
A multi-spectral instrument similar to the Mars2020 SuperCam suite (with stand-off LIBS, Raman,
VISIR, and fluorescence spectroscopies, and color context imaging) would provide multiple probes
to assess the habitability and astrobiological potential of interesting targets (Rees et al., 2019). Primary
and alteration mineralogy could be characterized using Raman spectroscopy and VISIR. LIBS
provides elemental abundances of target material, with potential to yield direct measure of
CHNOPS+Fe elements (Rees et al., 2019). These analyses would provide data required to address
Science Objective 1B. SuperCam’s remote microimaging (RMI) camera has a resolution of 60 µm at
1.5 m stand-off distance, which would allow the detection of ice (Objective 1A) and biofabrics
(Objective 2C; Table 1). The camera would require active illumination; we baseline a tungsten halogen
light with an optical system that projects a flat illumination of 10o for both RMI and the camera
(below). Organics could be determined with time-resolved fluorescence spectroscopy as organics
fluoresce when excited by the 532 nm laser (Objective 2A; Table 1). Fluorescence from organics
decays over very short timeframes (<1 ns to 200 ns), significantly shorter than fluorescence from
minerals (µs-ms), allowing detection and differentiation of organic and mineral components in the
Context imaging would be conducted via a camera like Mastcam-Z, which would allow for high
definition and 3D cave images when paired with an illumination source. Image resolutions vary
between 150 µm and 750 mm per pixel depending on distance. The camera would be able to capture
a range of images to map the extent of brines or ice in the cave and provide high resolution imaging
of the cave itself, which would determine cave size and extent (Objective 1A). The 3D information
extracted could further be used to characterize the geomorphometric parameters such as orientation,
slope, and surface roughness to enable safe rover maneuvering.
Technological Development
Key technological developments for instrumentation would further aid Mars cave exploration
including autonomous sample selection and data processing. Communication between the robotic
platform and Earth may be limited due to bandwidth restrictions between the rover and relay points
(e.g. deployable relays or orbiting assets); therefore, mission operations may require autonomous
sample selection to vet targets before measurement with resource-intensive instruments. Additionally,
science data collected throughout the mission may need to be processed or interpreted onboard to
prioritize downlinking the most valuable science data in cases of bandwidth-restricted mission
architectures. MACIE would benefit from advances in autonomous sample selection using machine-
learning algorithms currently being advanced for the Europa Lander and through DoD projects.
MACIE Mission Architecture and Concept of Operations (ConOps)
Site Selection
Cave site selection would be based on expected habitability and astrobiological potential, as
defined by smaller entrance opening, longer subsurface cavity lateral extent (Howarth, 1980),
and persistence of water ice (Williams et al., 2010).
Determining subsurface lava tube expression (entrance angle, size, shape, and lateral extent) remains
challenging. Roughly 60% of the Mars Global Cave Candidate Catalog remains unimaged by high-
resolution instruments. The low roll angle of Mars Reconnaissance Orbiter (MRO 30°), which
hinders the ability of High-Resolution Imaging Science Experiment (HiRISE) to image as obliquely
as Lunar Reconnaissance Orbiter Camera (LROC 40°), combined with the current lack of coverage
Mission Concept for Mars Subsurface Life and Habitability
over candidate cave sites may have led to a bias in
the available dataset toward vertical entrances.
Some horizontal entrances have been identified,
which would allow lateral entrance to a cave
(Cushing written comm., 2020)
Geophysical methods such as radar, gravity, and
magnetic field analyses could help link candidate
cave entrances with subsurface void spaces of lateral
extent. These methods are sensitive to changes in
subsurface structure. Shallow Radar (SHARAD)
and Mars Advanced Radar for Subsurface and
Ionosphere Sounding (MARSIS) orbital sounders
are long-lived experiments with a high combined
surface coverage. Preliminary SHARAD results
suggest this sounder can detect subsurface
interfaces at tube ceilings 5-7 m below the surface and with diameters of 2-12 m (Perry et al., 2019).
Context camera (CTX) visual and THermal Emission Imaging System (THEMIS) infrared imaging at
Alba Mons, just north of the Tharsis region, mapped candidate cave entrances and possible lava tube
extents and indicated volcanogenic flanks where lava tubes were observed and had shallow slopes <1o,
which suggests cave traverse difficulty would be insignificant, not accounting for the rockiness of the
floor material (Perry et al., 2019; Figure 1). Ongoing radar reconnaissance is essential in
characterizing lava tube morphologies and extents and would inform MACIE’s site selection
and design constraints.
MACIE Mission Architecture
MACIE’s configuration builds on knowledge of subsurface void spaces on Earth, the Moon, and
Mars. Several existing mission architecture options could be adapted to target the Martian subsurface
(Figure 2). Axel, featured in the MoonDiver Discovery Class Mission proposal targeting lunar pits,
is a mature technology (technology readiness level; TRL 6) developed to explore vertical entrances
known to exist on the Moon and Mars (Nesnas et al., 2020). The ambulatory Spot rover (TRL 5)
deployed in a current DARPA SubT competition (Bouman et al., 2020) could be tethered for a vertical
entrance. Lateral entrances would not necessitate tethering, reducing risk. Precision landing (>150 m
from an entrance) could be used to minimize surface travel prior to exploring the cave.
Remotely operated aerial systems (UAS), like the Mars2020 helicopter, could be used in either a
precursor scouting mission (Bapst et al., 2020) or as part of a mission where it is paired with a rover.
UAS would survey the area and assess the best cave to explore from risk and science perspectives (Fan
et al., 2019; Kanellakis et al., 2020; Sasaki et al., 2020;). In addition, such UAS could be equipped with
(1) thermal cameras for detection and comparative analysis of caves and (2) hyperspectral cameras for
providing geological/mineralogical information of the surface. UAS, which provide high-resolution
oblique images, can also enable 3D terrain modelling with high precision, accuracy, and resolutions
(Sam et al., 2020) to enable safe and efficient rover approach to the entrance.
Robotic and Autonomy Technology Development
Robotic and artificial intelligence technologies targeting mapping, target selection, and chemical
analysis have matured sufficiently to prepare us to explore a Martian cave. The DoD’s DARPA
Subterranean (SubT) Challenge has fueled autonomous technology demonstration for cave
exploration (Agha-mohammadi et al., 2019) including (1) mobility in unknown, rugged terrains,
narrow passages, and vertical shafts (Bouman et al., 2020), (2) perception (GPS-denied navigation and
autonomous motion for >100 m) (Ebadi et al., 2020, Santamaria-Navarro et al., 2019), (3) autonomy
Figure 1: Mapped candidate cave entrances and possible
lava tube extents at Alba Mons (40.5oN 250.4oE), just
north of the Tharsis region indicate lava tubes had shallow
slopes <1o (from Perry et al., 2019). This suggests lava
tubes will have relatively minimal slopes, enhancing
Mission Concept for Mars Subsurface Life and Habitability
(adapting to terrain and assessing risk without ground
communication) (Kim et al., 2019; Otsu et al., 2020),
and (4) communication for exploring subsurface
voids. Additional technological developments in these
areas would enhance MACIE’s operations and reduce
mission cost and risk.
5. Cost Justification
Leveraging the precision-landing heritage from
Mars2020 and Mars Sample Return, we anticipate
judicious site selection, continuing
advancements in robotics, and autonomous
sampling and robotic operations would allow
MACIE to fit New Frontiers class mission within
this decade. However, on the basis of a preliminary
concept study we conducted this year, a true-life
detection mission to a Martian cave would exceed a
New Frontiers cost cap and bump up to Flagship
Mission cost.
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... Planetary exploration has benefited from advancements in robotics through automation of data collection for planetary science and robotic precursor missions for human space exploration [1]. To date, robotic precursor missions have engaged in surface exploration of Mars [2] but have not explored subsurface environments despite the potential geological and astrobiological significance of these domains [3,4]. As a result, robotic subsurface exploration has been identified as a key technology for future missions to these planets [5]. ...
... Exploration frameworks cannot assume a priori knowledge about the structure of the environment so the exploration system must operate with unknown locomotion constraints. Aerial robots have recently been leveraged to mitigate these constraints in the subterranean domain [8] and considered for subsurface mapping on Mars [3]. In this work, we consider aerial robots operating in a cave on Earth (Fig. 1) as an analog scenario for subsurface exploration on Mars. ...
This paper develops a communication-efficient distributed mapping approach for rapid exploration of a cave by a multi-robot team. Subsurface planetary exploration is an unsolved problem challenged by communication, power, and compute constraints. Prior works have addressed the problems of rapid exploration and leveraging multiple systems to increase exploration rate; however, communication considerations have been left largely unaddressed. This paper bridges this gap in the state of the art by developing distributed perceptual modeling that enables high-fidelity mapping while remaining amenable to low-bandwidth communication channels. The approach yields significant gains in exploration rate for multi-robot teams as compared to state-of-the-art approaches. The work is evaluated through simulation studies and hardware experiments in a wild cave in West Virginia.
... Before sending a robotic mission [15] or astronauts to a specific lava tube, it would be desirable to scout and map several locations. Mars helicopters are candidate platforms to scout multiple lava tubes throughout a single mission. ...
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Due to their resilience to motion blur and high robustness in low-light and high dynamic range conditions, event cameras are poised to become enabling sensors for vision-based exploration on future Mars helicopter missions. However, existing event-based visual-inertial odometry (VIO) algorithms either suffer from high tracking errors or are brittle, since they cannot cope with significant depth uncertainties caused by an unforeseen loss of tracking or other effects. In this work, we introduce EKLT-VIO, which addresses both limitations by combining a state-of-the-art event-based frontend with a filter-based backend. This makes it both accurate and robust to uncertainties, outperforming event- and frame-based VIO algorithms on challenging benchmarks by 32%. In addition, we demonstrate accurate performance in hover-like conditions (outperforming existing event-based methods) as well as high robustness in newly collected Mars-like and high-dynamic-range sequences, where existing frame-based methods fail. In doing so, we show that event-based VIO is the way forward for vision-based exploration on Mars.
... Recently, there has been increasing interests in the exploration of Martian volcanic (lava tube) as compelling astrobiological targets (Léveillé and Datta, 2010;O'Connor et al., 2021;Popa et al., 2012;Sauro et al., 2020). One of the interesting questions for future missions (Phillips-Lander et al., 2021) is to find evidence of water-rock interactions to get insights on whether liquid water was present in the Martian caves over geologic time, as water is essential to the life that we know of. Our results show that cave water chemistry is strongly controlled by the interactions between liquid water and host rock, and evaporative concentration was an important factor for precipitation of secondary SiO 2(am) -rich speleothems in the terrestrial volcanic caves at Lava Beds, as shown by the forward reaction model. ...
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.
... This feature would likely become a high priority target for groundtruthing. For Mars, a small number of aggregated pixels representing a potential cave may be a low priority target for further examination as a human shelter or storage depot, but potentially a higher priority target for robotic exploration-as it may be more buffered from the surface environment (e.g., [96,97]). Thus, the grouping of pixels with cave-like thermal signatures into clusters will enable workers to prioritize which potential cave localities require further examination (i.e., physical groundtruthing of terrestrial caves or additional imagery interpretation for planetary caves). ...
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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.
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  • Bouley
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