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

6
Mars: Evolution of an Earth-like World
Mars has a unique place in solar system exploration: it holds keys to many compelling planetary
science questions and it is accessible enough to allow rapid, systematic exploration to address and answer
these questions. The scientific objectives for Mars center on understanding the evolution of the planet as
a system, focusing on the interplay between the tectonic and climatic cycles and the implications for
habitability and life. These objectives are well aligned with the broad crosscutting themes of solar system
exploration articulated in Chapter 3.
Mars presents an excellent opportunity to investigate the major question of habitability and life in
the solar system. Conditions on Mars, particularly early in its history, are thought to have been conducive
to formation of prebiotic compounds and potentially to the origin and continued evolution of life. Mars
has also experienced major changes in surface conditions, driven by its thermal evolution, orbital
evolution, and by changes in solar input and greenhouse gases, that have produced a wide range of
environments. Of critical significance is the excellent preservation of the geologic record of early Mars,
and thus the potential for evidence of prebiotic and biotic processes and how they relate to evolution of
the planet as a system. This crucial early period is when life began on Earth, an epoch largely lost on our
own planet. Thus, Mars provides the opportunity to address questions about how and whether life arose
elsewhere in the solar system, about planetary evolution processes, and about the potential coupling
between biological and geological history. Progress on these questions, important to both the science
community and the public, can be made more readily at Mars than anywhere else in the solar system.
The spacecraft exploration of Mars began in 1965 with an exploration strategy of flybys,
followed by orbiters, landers, and rovers with kilometers of mobility. This systematic investigation has
produced a detailed knowledge of the planet’s character, including global measurements of topography,
geologic structure and processes, surface mineralogy and elemental composition, the near-surface
distribution of water, the intrinsic and remnant magnetic field, gravity field and crustal structure, and the
atmospheric composition and time-varying state (Figure 6.1). 1 The orbital surveys framed the initial
hypotheses and questions and identified the locations where in situ exploration could test them. The
surface missions—the Viking landers, Pathfinder, Phoenix, and the Mars Exploration Rovers—have
acquired detailed information on surface morphology, stratigraphy, mineralogy, composition, and
atmosphere-surface dynamics and confirmed what was strongly suspected from orbital data: Mars has a
long-lasting and varied history during which water has played a major role.
A new phase of exploration began with the Mars Express and Mars Reconnaissance (MRO)
orbiters, which carry improved instrumentation to pursue the questions raised in the earlier cycles of
exploration. Among the discoveries (Table 6.1) is the realization that Mars is a remarkably diverse planet
with a wide range of aqueous environments (Figure 6.2). The role of water and the habitability of the
ancient environment will be further investigated by the Mars Science Laboratory (MSL), scheduled for
launch in 2011, which will carry the most advanced suite of instrumentation ever landed on the surface of
a planetary object (Box 6.1).
The program of Mars exploration over the past 15 years has provided a framework for systematic
exploration, allowing hypotheses to be formulated and tested and new discoveries to be rapidly and
effectively pursued with follow-up observations. In addition, the program has produced missions that
support each other both scientifically and through infrastructure, with orbital reconnaissance and site
selection, data relay, and critical event coverage significantly enhancing the quality of the in situ
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