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Influence of the Cave Environment on Habitability & Biosignatures: Implications for Finding Life on Mars

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Abstract for the 2019 Astrobiology Science Conference, 24-28 June 2019, Bellevue, WA.
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Influence of the Cave Environment on Habitability & Biosignatures: Implications for Finding Life on Mars
C. M. Phillips-Lander1, J. J. Wynne2, A. Stockton3
1Space Sci. and Eng., Southwest Research Institute, San Antonio, TX (; 2Dept of Bio. Sci.,
Merriam-Powell Center, Northern Arizona University; 3Dept. of Chemistry and Biochemistry, Georgia Tech.
Introduction: Subterranean environments, particularly
caves that may be easily accessed without expensive
drilling payloads, have been identified by the National
Academies Astrobiology Strategy [1] as high priority
astrobiological targets. Lava tubes are quite common on
Earth and have been observed in Hesperian to
Amazonian terrains on Mars [2-4]. To date, over 1,000
Martian caves have been identified [5]. These lava tube
caves are considered “special regions” [5] which may
serve as past or current refugia on Mars because (a) they
act as preferential conduits for water flow [6], (b) they
maintain stable, habitable, environmental conditions
over extended periods, which are likely to be
significantly different from surficial conditions, and (c)
they provide protection from UV and cosmic radiation
[7]. However, a key limitation inhibiting our
examination of these environments on Mars is our
inability to predict which subterranean environments
broadly, and which cave environments specifically,
yield the greatest habitability. We seek to determine
which environmental factors most strongly influence
microbial colonization and biosignature formation (Fig
1). Results from this and on-going research will aid in
determining which caves are the best candidates for a
future martian cave mission.
Cave Environment and Habitability: A variety of lava
cave climates may be present in Mars’ subsurface. We
compared chemical and biological weathering in four
spatially co-located lava caves at Craters of the Moon
National Monument, ID. These caves represent
warm/dry (SJD), warm/wet (Pond), cold/wet (Ice Lake)
and cold/damp (Spongy Floor) conditions, respectively.
Our results indicate temperature, chemistry, and nutrient
availability influence microbial colonization of these
subsurface environments. However, water and light
availability demonstrated no similar influence.
Biosignatures: Amorphous silica, calcite, and Fe-oxides
occur as alteration phases in SJD. Fe-oxides and
amorphous silica are associated with microbial surfaces
in SJD, suggesting they may be microbially induced
precipitates similar to what has been observed in other
systems [8].
Cave Identification: Techniques for detecting caves
using airborne/ spacecraft-acquired thermal imagery
have improved markedly over the past 50 years. In
particular, Wynne et al. [9] demonstrated the relevance
of terrain analysis algorithms as spectral enhancement
techniques of thermal imagery. These advances are
largely due to a combination of higher instrument
sensitivity, modern computing systems, and processor-
intensive analytical techniques. Reliable detection of
caves will enable us to prioritize caves for human
habitation on the Moon and Mars [10], and selecting the
best candidates to search for evidence of life on Mars [9,
While cave detection techniques have clearly improved,
additional research in multispectral analysis should be
pursued. Additionally, methods for detecting laterally
trending cave entrances with nadir-captured imagery
require further development and testing. Finally, we need
to resolve how topographic shadowing may confound
reliable cave detection, as well as examine the
relationship between thermal signature strength and cave
Implications for Cave Site Selection: Significant work
remains to synthesize these data to create systematic cave
site selection criteria for a martian cave mission. Accurate
remote detection and evaluation of candidate caves will
further bolster the likelihood of mission success. We
envision future research entailing advancements in
habitability and biosignature analysis correlated with cave
geometries will allow us to determine the best places to
conduct an astrobiological cave mission to Mars.
References: [1] Nat’l Academies (2018). [2] Hodges and
Moore (1994) USGS Prof. Paper 1534. [3] Cushing et al.
(2007) GRL 34. [4] Leone (2014) J. of Volcano. &
Geothermal Rsh., 277, 1-8. [5] Cushing and Titus (2018)
USGS Tech. Rpt. [6] Léveillé and Data (2010) Planet.
and Space Sci., 58, 592-598. [7] Boston et al. (2001)
Astrobio., 1, 25-55. [8] Phillips-Lander et al. (2014)
Geomicro. J. 31, 23-41. [9] Wynne et al. (2016) EOS 97.
[10] Wynne et al. (2016) 2nd It’l Planet. Caves Conf.,
Abstract #9029.
Figure 1: Our work will integrate multiple
environmental parameters effects on microbial
colonization and activity to create site selection criteria
for a martian cave mission.
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