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

• What are the inventories and distributions of volatile elements and compounds (species
abundances and isotopic compositions) in the mantles and crusts of the inner planets?
• What are the elemental and isotopic compositions of species in Venus’s atmosphere,
especially the noble gases and nitrogen-, hydrogen-, carbon- and sulfur-bearing species? What was
Venus’s original volatile inventory and how has this inventory been modified during Venus’s evolution?
How and to what degree are volatiles exchanged between Venus’s atmosphere and its solid surface?
• Are Venus’s highlands and tesserae made of materials suggestive of abundant magmatic
water (and possibly liquid water on the surface)?
Future Directions for Investigations and Measurements
Key to constraining the character of volatile chemical compounds on Venus, the Moon and
Mercury are determining (1) the state, extent, and chemical and isotopic compositions of surface volatiles
particularly in the polar regions on the Moon and Mercury; (2) the inventories and isotopic compositions
of volatiles in the mantles and crust of all the terrestrial planets; and (3) the fluxes of volatiles to the
terrestrial planets (e.g., by impact) over time. Of high importance for Venus is to obtain high-precision
analyses of the light stable isotopes (especially carbon, hydrogen, oxygen, nitrogen, and sulfur) in the
lower atmosphere and noble gas concentrations and isotopic ratios throughout its atmosphere. Also key is
the continued evaluation of the effects of meteoroid impact fluxes and intensities on the development and
evolution of life on the inner planets through analysis of the impact record on the Moon and Mercury.
Understand the Effects of Internal Planetary Processes on Life and Habitability
It is crucial to understand how planetary environments can enable or inhibit the development and
sustainment of prebiotic chemistry and life. This objective focuses on the availability of accessible
energy and nutrients (chemicals and compounds), and the establishment and maintenance of clement
stable environments in which life could have arisen and flourished. Also important are the initiation and
termination of planetary magnetic fields, which can enable shielding of a planet’s surface from external
radiation.
Despite the dearth of spacecraft missions to explore the inner planets in the past decade, there
have been several important discoveries about internal processes. Recent flybys of Mercury by
MESSENGER have confirmed the dipole field measured by Mariner 10. Flyby data also confirm that
Mercury’s plains are volcanic, and show that some are far younger than previously proposed. Further
improvements in our knowledge of Mercury’s internal structure and geologic history are expected after
MESSENGER enters its mapping orbit in 2011.
Constraints on Venus’s current tectonic style and extensive volcanism are based mostly on radar
imagery and altimetry from the Magellan mission. Recent results from the VIRTIS spectrometer on the
Venus Express spacecraft provide evidence that Venus’s tesserae are more felsic than mafic, and that
Venus’s volcanoes have been active in the geologically recent past (consistent with models of gradual
rather than catastrophic resurfacing). For the Moon, although much of what was learned about its interior
in the Apollo era remains intact, new evidence of volatiles in lunar magmas is altering that view.
Important Questions
Some important questions concerning the effects of internal planetary processes on life and
habitability include the following:
• What are the timescales of volcanism and tectonism on the inner planets?
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