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

VIRTIS spectrometer on the Venus Express spacecraft show that resurfacing processes have continued as
recently as 2 million years ago. 9 MESSENGER’s flybys of Mercury have provided views of the regions
unseen by Mariner 10 and indicate a more dynamic surface history than previously thought. The diversity
of terrains observed by MESSENGER suggests a complex evolution, including extensive tectonism and
young volcanism and pyroclastic activity. 10
Important Questions
Some important questions concerning characterizing planetary surfaces to understand how they
are modified by dynamic geologic processes include the following:
• What are the major surface features and modification processes on each of the inner planets?
• What were the sources and timing of the early and recent impact flux of the inner solar
system?
• What are the distribution and timescale of volcanism on the inner planets?
• What are the compositions, distributions, and sources of planetary polar deposits?
Future Directions for Investigations and Measurements
Major advances in our understanding of the geologic history of the inner planets will be achieved
in the coming decade through orbital remote sensing of Venus, the Moon and Mercury, as well as in situ
data from Venus and the Moon. Key among these are global characterization of planetary morphology,
stratigraphy, composition, and topography, modeling the time variability and sources of impacts on the
inner planets and continued analysis of sample geochronology to help provide constraints on the models.
Also crucial is developing an inventory and isotopic composition of lunar polar volatile deposits to
understand their emplacement and origin, modeling conditions and processes occurring in permanently
shadowed areas of the Moon and Mercury and continued observation of Mercury’s volatile deposits to
understand their origin.
UNDERSTAND HOW THE EVOLUTION OF TERRESTRIAL PLANETS
ENABLES AND LIMITS THE ORIGIN AND EVOLUTION OF LIFE
Is Earth the only planet that has (or had) life? Understanding how the evolution of the terrestrial
planets enables and limits the origin and evolution of life is closely aligned with other NASA efforts,
including astrobiology and Mars exploration. This goal is also is relevant to the study of Mars, moons
like Europa, Enceladus, and Titan, and terrestrial planets orbiting stars other than the Sun.
The existence of life, present or past, depends on planetary context and the availability of energy,
nutrients, and clement environments. Thus, it is crucial to explore the inner solar system in great detail in
order to understand the constraints on and possible timing of habitable conditions. The Moon and
Mercury are unlikely to harbor life, but they provide critical records of processes and information about
the early solar system when life emerged on Earth. Earth is the single known planet that provided all the
necessities for the origin and persistence of life, but Venus may have once supported oceans of liquid
water and so, possibly, life. Similarly, Mars’s surface shows signs of abundant water in its distant past,
and may likewise have supported life. Finally, learning about the circumstances that limit or promote the
origin and evolution of life will inform current understanding of extrasolar planets and the search for life
in the universe.
Fundamental objectives that will help understand how the evolution of terrestrial planets enables
and limits the origin and evolution of life are as follows:
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