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

Abstract

MACIE, a potential New Frontiers class mission concept named after Macie Roberts one of NASA’s human computers, will address two science goals: 1) Have habitable conditions ever existed within Martian lava tubes? And 2) did life emerge or seek refuge in Martian lava tubes? We are currently evaluating the instrument and architecture trade space using mission concept development tools and subject matter experts at NASA JPL and will emerge with a viable CML2- 3 concept that will address MEPAG goals (2020): 1) Determine whether life ever existed on Mars and 2) Characterize the climate of Mars. Importantly, if MACIE does not detect evidence of past or present life, it would still provide significant habitability and geology science returns, and enable future use as a human astronaut shelter or base. To participate in a co-signer to help improve the possibility of robotic exploration of a Martin cave, go to: https://docs.google.com/forms/d/e/1FAIpQLSfDRpCJ7SlmTWcT0WYbBOiE6ePaNe20V9FfBFUPbvDSn27tLw/viewform
Mars Astrobiological Cave and Internal habitability Explorer (MACIE):
A New Frontiers Mission Concept
A white paper planned for the upcoming Decadal Survey on Planetary Science and Astrobiology
Submitted to MEPAG meeting 38 for advertisement to the Mars community
By: C. M. Phillips-Lander (charity.lander@swri.edu), J. J. Wynne, N. Chanover, C. Demirel-
Floyd, K. Uckert, K. Williams, T. N. Titus, J. Blank, P. Boston, K. Mitchell, A. Kereszturi, J.
Martin-Torres, D. Wyrick, S. Shkolyar, K. Retherford
Caves represent one of the best localities for finding evidence of life beyond Earth. These
features offer subsurface access without the costs of a deep drilling payload. There have been
more than a thousand cave-like features identified on Mars. They formed from volcanic processes
(e.g. lava tubes), tectonic processes (e.g. atypical pit crater chains), or both. Numerical heat and
mass transfer modeling of the Martian subsurface indicates that equatorial Martian lava tube
caves may not only be shielded from cosmic radiation but also host favorable conditions to
maintain stable water-ice deposits. Therefore, these features represent significant astrobiological
targets on Mars.
MACIE, a New Frontiers class mission concept named after Macie Roberts one of NASA’s
human computers, will address two science goals: 1) Have habitable conditions ever existed
within Martian lava tubes? And 2) did life emerge or seek refuge in Martian lava tubes? We will
specifically focus on lava tubes in the Tharsis Region of Mars, which may have been glaciated
through most of the Amazonian (to ~300 Mya; Parsons et al., 2020), and some lava tubes in the
region are thought to host stable water ice (Williams et al., 2010). We are examining mobility
platforms that will allow us to traverse a Martian cave to determine whether there is water and/or
water ice present, evidence of present or past aqueous alteration, a radiation environment
conducive to life, and nutrients and energy available to support life. MACIE will also determine
whether the candidate lava tube contains evidence consistent with past or present life, including
molecular complexity of organics, biominerals, biovermiculations, and the presence of biogenic
gases. Therefore, this mission concept will address a key recommendation of the 2019 National
Academies’ Astrobiology Strategy, “NASA’s programs and missions should reflect a dedicated
focus on research and exploration of subsurface habitability in light of recent advances... [in our
understanding of] the history and nature of subsurface fluids on Mars...”
We are currently evaluating the instrument and architecture trade space using mission concept
development tools and subject matter experts at NASA JPL and will emerge with a viable CML2-
3 concept that will address MEPAG goals (2020): 1) Determine whether life ever existed on Mars
and 2) Characterize the climate of Mars. Importantly, if MACIE does not detect evidence of past
or present life, it would still provide significant habitability and geology science returns, and enable
future use as a human astronaut shelter or base.
We expect to have a full draft of our white paper advocating for MACIE as a New Frontiers
mission concept for the next decade by late April 2020. Additional co-authors who focus on lava
tube science, Amazonian Mars, habitability and astrobiology, instrumentation, and robotics are
welcome, as are co-signers who are interested in supporting the mission concept.
You can co-sign MACIE here. If interested in co-authoring, please contact: clander@swri.org
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Potential Instruments
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Article
Volcanic (lava tube) caves at Lava Beds National Monument (N. CA, USA) provide a valuable terrestrial analog for volcanic caves on Mars and the Moon. Terrestrial volcanic caves host a diverse microbial life, liquid water, and a variety of secondary mineral deposits (speleothems) with diverse morphologies and chemical compositions. Speleothems may preserve records of past and present microbial life and signatures of paleoenvironmental changes in terrestrial volcanic caves. Distinguishing between speleothems via chemical processes and microbially-mediated processes in terrestrial volcanic caves will provide valuable insights for future exploration of martian volcanic caves. To elucidate the formation of speleothems, we studied the chemical makeup (inorganic and organic) of cave waters in seven volcanic caves of variable ages, temperature, moisture content, light intensity, and frequency of human visitation. Cave water was characterized by stable isotopic composition (δ¹⁸O and δ²H), concentrations of major and trace elements, cations, anions, and characteristics of dissolved organic matter (DOM). A forward reaction model (PHREEQC) was used to test possible pathways for secondary mineral precipitation that formed these speleothems. The source of cave water was primarily regional meteoric precipitation that entered the caves through cave openings or through the cave overburden and fractured basalt walls as indicated by cave floor puddle water line δ²H = 8.32*δ¹⁸O + 9.55 parallel to the global meteoric water line (GMWL, δ²H = 8.3*δ¹⁸O + 10). A line formed by cave ceiling drip water δ²H = 3.39*δ¹⁸O – 44.77 intersecting the GMWL indicated that the water may be undergoing evaporation within the caves. Silicate weathering was found to be a primary process resulting in cave water enriched in Si (22 ± 7 mg/L), and contained trace levels of Al, Fe, Zn, Li, Sr, Cu, B, V, Ba, Cr and Mn. Geochemical calculations indicated that cave waters were undersaturated with respect to both amorphous silica (SiO2am) and calcite (CaCO3) which were the major components of speleothems observed within the caves. Results of a forward reaction model showed that evaporation of cave waters could lower the solubility of SiO2am and CaCO3 by increasing their saturation and ultimately precipitate these two secondary minerals forming the speleothems. The cave water DOM was characterized by high concentrations of dissolved organic carbon (DOC, 12 ± 8 mg/L) with a molar C/N ratio ranging from 2 to 22. The DOM was found to be aromatic (SUVA254, 1.2–2.9 L/mg.m), terrestrially derived and humic-like (humification index, 7–26) and contained molecules of 100 Da and 5000 Da approximate molecular weight (AMU). Our results indicated that the terrestrially derived carbonaceous organic matter transported into the caves was not utilized for heterotrophic microbial metabolisms as DOC was accumulated over dissolved inorganic carbon (DIC). Both findings suggest that with minimal heterotrophy, chemo-litho-autotrophy may be important pathways that cycle the elements within these volcanic caves with low light conditions. Together, this study proposes a potential pathway of speleothem precipitation through the interaction of water, dissolved mineral constituents, and microbial life where dissolved ions are concentrated in cave drip water through cyclic condensation-vaporization processes. This work is part of a multi-disciplinary project Biologic Resource Analog in Low Light Environments (BRAILLE) funded by the NASA PSTAR Program (NNH16ZDA001N), which focuses on studying volcanic caves as terrestrial analogs for the Moon and Mars.
Chapter
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.
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