Vision and Voyages for Planetary Science in the - Solar System ...

availability, physicochemical factors (temperature, pH, Eh, fluid chemistry), and availability of biogenic
elements—vary among environments, and how did they influence the habitability of different sites?
• Which accessible sites favor preservation of any evidence of past habitable environments and
life? How did the major factors that affect preservation of such evidence—for example aqueous
sedimentation and mineralization, oxidation, radiation—vary among these sites?
• How have the factors and processes that give rise to habitable conditions at planetary and
local scales changed over the long term in concert with planetary and stellar evolution?
Future Directions for Investigations and Measurements
Central to addressing habitability-related questions is searching for future landing sites that have
both high habitability and biosignatures preservation potential (Box 6.2). Key here is identifying
accessible rocks that show evidence for formation in aqueous environments such as fluvial, lacustrine, or
hydrothermal systems. 20 An additional requirement is to be able to place the rock exposures in a
stratigraphic framework that will allow reconstruction of past environmental conditions. 21 Another key
aspect in understanding present and past habitability is to characterize the current geologic activity of the
martian interior. The long-term evolution of geologic processes, habitable environments, and life on
Earth have been closely linked. Accordingly, geophysical observations that contribute to our
understanding of the martian interior are important to the search for signs of martian life.
Ultimately our best understanding of present and past habitability will await the return to Earth of
carefully selected samples from sites that have the highest scientific potential for analysis in terrestrial
laboratories. Analyses of returned samples in Earth-based laboratories are essential in order to establish
the highest confidence in any potential martian biosignatures and to interpret fully the habitable
environments in which they were formed and preserved. 22,23
Key technological developments for surface exploration and sampling include modest-sized
rovers capable of selecting samples and documenting their context. These rovers should include imaging
and remote-sensing spectroscopy adequate to establish local geologic context and to identify targets.
Suggested capabilities include surface abrasion tool(s), arm-mounted sensors, and a rock core caching
system to collect suites of samples that meet the appropriate standards. 24 The in situ measurements used to
select samples for return to Earth must go beyond identifying locations where liquid water has occurred. 25
They should also characterize the macroscopic and microscopic fabrics of sedimentary materials, be
capable of detecting organic molecules, reconstruct the history of mineral formation as an indicator of
preservation potential and geochemical environments, and determine specific mineral and chemical
compositions as indicators of organic matter or coupled redox reactions characteristic of life.
Also essential to better understand the geochemistry of martian environments and the
compositional and morphologic signatures these different environments produce is the continuation of a
robust R&A program. Theoretical, laboratory, and terrestrial analog studies should develop models,
analysis approaches, and instrumentation to interpret ancient environments from orbital, in situ, and
returned sample data 26,27,28
Assess Whether Life is or Was Present on Mars and Characterize Carbon Cycling
and Prebiotic Chemistry in a Geochemical Context
Assessing whether life is or was present on Mars will include characterizing complex organics,
the spatial distribution of chemical and isotopic signatures, the morphology of mineralogical signatures,
and identifying temporal chemical variations requiring life. Characterizing the carbon cycle will include
determining the distribution and composition of organic and inorganic carbon species, characterizing the
distribution and composition of inorganic carbon reservoirs through time, characterizing the links
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