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

planets and for understanding subsequent processes such as accretion, magma oceans, differentiation,
core convection, dynamo generation, partial melting and volcanism. Mars, the Moon, Venus, and
Mercury are linked by similar bombardment histories, and all contain evidence for volcanism,
differentiation and early crustal growth. Of these inner planets, Mars has evidence of an early dynamo
process, absent on Venus and the Moon. Thus, Mars provides information on the early stages of planet
formation and heat-loss mechanisms that are crucial for putting the differentiation history, bulk chemistry
and geophysical properties of all of the inner planets, including Earth, in context.
To Extrasolar Planets
Mars provides a unique alternative to Earth as a leading potential example of a planet that has
been habitable in the past, at least episodically. Therefore, it is especially interesting with regard to our
understanding of the habitability of extrasolar terrestrial planets and the likeliness of life elsewhere. In
particular:
• Mars has a low mass/radius relative to Earth and therefore expands the possible range of
silicate extrasolar planet mass/radius values that may be targeted for habitability;
• The potential discovery of habitable regions on Mars forces us to expand the concept of the
classic “habitable zone” 75 within planetary systems;
• Ancient Mars was probably a case of a relatively dry planet (no global oceans) with an
environmental regime fundamentally different than that of our planet, and which we can study through the
geological records; and
• The fact that Mars has lost its ability to sustain liquid water teaches us lessons about possible
processes that may prevent many extrasolar planets from remaining habitable.
To Human Exploration
Mars is the only planet in the solar system that is realistically accessible to human exploration,
and has been proposed as a target for orbital flybys and future landing by human explorers. To reduce the
cost and risk for future human exploration, robotic precursor missions would be needed to acquire
information concerning potential resources and hazards, perform technology and flight system
demonstrations, and deploy infrastructure to support future human exploration activities. The elements of
the Mars Sample Return campaign, beginning with MSL, will provide crucial data for landing significant
mass, executing surface ascent and return to Earth, and identifying potential hazards and resources. 76
IMPORTANCE OF MARS SAMPLE RETURN
For the past three decades, the scientific community has consistently advocated the return of
geological samples from Mars. Summaries of the literature on this topic appear in the extensive writings
of the NRC, 77 several major recent reports by MEPAG, 78 and a significant recent contribution by the
International Mars Exploration Working Group. 79 Numerous white papers submitted to the NRC Decadal
Survey indicated substantial community support via signatories and addressed the importance and
significance of Mars Sample Return as the keystone of future Mars exploration. 80
The committee, building on numerous community assessment groups, open discussions, and
white papers, places as the highest priority Mars science goal to address in detail the questions of
habitability and the potential origin and evolution of life on Mars. The committee carefully considered
the alternative of several rover missions instead of sample return. It is our opinion that sample return
would have significantly higher science return and a much higher science-to-dollar ratio. Thus, a critical
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