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

particularly the polar-layered deposits. 46 In order to follow up on scientific results and discoveries from
the Phoenix and Mars Reconnaissance Orbiter missions an in situ analysis of laterally or vertically
resolved measurements of grain size, dust content, composition, thickness and extent of layers, elemental
and isotopic ratios relevant to age (e.g., deuterium/hydrogen) and astrobiology (CHNOPS) should be
performed.
DETERMINE THE EVOLUTION OF THE SURFACE AND INTERIOR
Determining the composition, structure, and history of Mars is fundamental to understanding the
planet as a whole, and provides the context for virtually every aspect of the study of conditions of
habitability and the potential for the origin and persistence of life.
The specific objectives of the geology goal are to:
• Determine the nature and evolution of the geologic processes that have created and modified
the martian crust over time; and
• Characterize the structure, composition, dynamics, and evolution of Mars’s interior.
Subsequent sections examine each of these objectives in turn, identifies important questions to be
addressed, and future investigations and measurements that could provide answers.
Determine the Nature and Evolution of the Geologic Processes
that Have Created and Modified the Martian Crust over Time
The study of geologic processes will include investigating the formation and modification
processes of the major geologic units, constraining the absolute ages of these processes, exploring
potential hydrothermal environments, characterizing surface-atmosphere interactions, determining the
tectonic history and structure of the crust, determining the present distribution of water on Mars,
determining the nature and origin of crustal magnetization, and evaluating the effect of large-scale
impacts. Despite our rich knowledge of martian surface properties, many questions remain about the
nature of the surface and interior processes. Mars is the object in our solar system most similar to Earth,
and insights into its history and evolution will inform our understanding of our planet’s origin and history.
Research over the past decade has resulted in a new integrated understanding of Mars as a
dynamic geologic system that has changed significantly over time. 47 In this context martian geologic
history can be divided in ancient, transitional, and recent periods, with modern Mars, as observed today,
providing insights into past processes and conditions.
Unlike Earth, a substantial fraction of the exposed terrain of Mars is inferred to be older than
~3.5-3.7 billion years (Noachian period). These terrains are represented by topographically high,
extensively cratered surfaces that dominate the southern latitudes and provide a unique geologic record of
the early stages of planet formation and possibly of the origin of prebiotic chemicals and life. Ancient
Mars was marked by the presence of near-surface liquid water, with evidence for standing water, lakes,
valley networks, and thick, layered sequences of sedimentary rocks with internal stratification. 48
Secondary minerals on the surface of Mars, including Fe-oxides/hydroxides/oxyhydroxides, hydrous
sulfates, carbonates, phyllosilicates, and chlorides have been found by orbiters and surface missions and
in martian meteorites. These minerals occur in thick, layered sedimentary units, in the soil, and in
cements, veins, and rinds in individual rocks (Figure 6.5). The diversity of these mineral assemblages has
been hypothesized to result from significant differences in the chemistry of the waters (brines), pH and
water availability. 49 Whether or not these represent a general temporal trend 50 or more complex
relationships remains uncertain (Figure 6.6). 51
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