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

and core compositions? How has Mars’s internal structure affected its magmatism, atmosphere, and
habitability?
Future Directions for Investigations and Measurements
Major progress in understanding Mars’s interior requires obtaining key geophysical data through
a network. 72 Seismic data will enhance understanding of the martian interior structure, including present
lithosphere/crust structure and thickness, the current seismic and volcanic activity, the depth of crustal
magnetization, the basal structures of the crust under large topographic highs (e.g., Tharsis and Elysium)
and lows (e.g., Hellas Basin), and place boundary conditions on models of the early thermal profiles, heat
flows and geologic evolution. Also we need to acquire other geophysical data (e.g., heat flow and
magnetic sounding) to better constrain the mineralogical, density and temperature structure of the martian
interior.
INTERCONNECTIONS
To Earth and the Terrestrial Planets
Mars is unique in solar system exploration because it has had processes comparable to Earth
during its formation, interior evolution, surface modification, geochemical alteration, and atmospheric
and climate evolution. Crucially, and perhaps uniquely, the martian surface preserves a record of the
early solar system history on a planet with water and an atmosphere in which the conditions may have
been similar to those on Earth when life originated. This record has been obliterated on Earth during
crustal recycling related to plate tectonics. Mars records critical information that can provide a means to
approach (and possibly answer) questions about the environmental conditions that may have accompanied
the origin and evolution of life, short and long-term climate change, in comparison to Earth, and the early
evolution and origin of the terrestrial planets.
When and how life began on Earth is not yet known. Evidence for early life on Earth has been
reported in rocks at least as old as 3.7 billion years. 73 The general processes by which the inventory of the
basic building blocks of life was assembled, how those pre-biotic components were chemically
reorganized, and how replicating life forms originated and evolved all took place during the critical time
period before 3.5 Ga. However, for the first billion years of Earth’s history, our ability to read the
geologic record is either fragmentary or non-existent. Mars has a number of characteristics that make it
the most probable location for pre-biotic processes to have occurred and for that record to be preserved.
Mars is in the “habitable zone” around our host star, it likely had liquid water at some points in the past,
and it might have had a thicker atmosphere that protected the prebiotic and biotic material from radiation.
Mars today contains the essential ingredients to support and sustain life, and the geologic record shows
numerous promising ancient habitable environments. 74
The martian atmosphere is a simpler system than Earth, but it is also the most Earth-like of all the
planetary atmospheres. This provides the opportunity to validate climate and atmospheric circulation
models and to test these models of physical systems with different boundary conditions. Mars’s
atmosphere has evolved significantly with time. It shows clear evidence for periodic climate change,
which, combined with calculations of the effects of large excursions in orbital parameters, all point to
significant changes in insolation driving major redistributions of water over the planet in cyclic episodes
that are analogous to Earth’s ice ages.
The inferred origins and evolution of the four terrestrial planets are as varied as their surfaces and
current environments. Mars is unique in the accessibility and comparative hospitability of its surface
relative to Venus and Mercury. Its level of historical thermal and geological activity, intermediate
between Earth and the Moon, is ideally suitable both for elucidating the initial conditions of the terrestrial
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6-20