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

Important Questions
Some important questions concerning how solar energy drives atmospheric circulation, cloud
formation and chemical cycles that define the modern climate balance on terrestrial planets include the
following:
• What are the influences of clouds on radiative balances of planetary atmospheres, including
cloud properties: microphysics, morphology, dynamics and coverage?
• How does the current rate of volcanic outgassing affect climate?
• How do the global atmospheric circulation patterns of Venus differ from those of Earth and
Mars?
• What are the key processes, reactions and chemical cycles controlling the chemistry of the
middle, upper and lower atmosphere of Venus?
• How does the atmosphere of Venus respond to solar-cycle variations?
Future Directions for Investigations and Measurements
Processes controlling the current climates of the terrestrial planets must be characterized to
interpret and reconstruct their climate histories. These data will be incorporated into a new generation of
planetary GCMs that will increase the ability of terrestrial GCMs to predict climate and thereby improve
understanding of anthropogenic effects. Investigations for the coming decade should include
measurement of the influence of clouds on radiative balances at Venus with both in situ and orbital
investigations including cloud microphysics, morphology, dynamics and coverage, and elucidation of the
role of volcano-climate interactions. It will be important to better explain Venus’s global circulation
within the theoretical framework of modeling techniques developed for terrestrial GCMs and to
understand the chemistry and dynamics of Venus’s middle atmosphere. This includes characterizing the
photochemistry of chlorine, oxygen, and sulfur on Venus and measuring current atmospheric escape
processes at Venus with orbital and in situ investigations. To better understand Earth’s climate we must
carefully compare the solar cycle responses of the upper atmospheres, exospheric escape fluxes and
climates.
Characterize the Record of and Mechanisms for Climatic Evolution on Venus
with the Goal of Understanding Climate Change on Terrestrial Planets,
Including Anthropogenic Forcings on Earth
Progress has been made over the last decade in understanding the changes and evolution of
terrestrial planet climates. The Venus Express mission 13 and results from the Galileo fly-by of Venus 14
have provided tantalizing evidence that Venus’s highlands may be more evolved (i.e., more silicic) than
the volcanic plains. These results could signify that at some time in the past, evolved, hydrous magmas
were erupted on Venus, and that the highland material may represent remnant continental crust.
Recent results for the other inner planets have placed better constraints on rates and mechanisms
of volatile loss (e.g., MESSENGER spacecraft data on Mercury’s exosphere and Venus Express SPICAV
results for Venus hydrogen and oxygen loss). MESSENGER observations of Mercury’s surface suggest
that pyroclastic deposits may be as young as 1 billion years, and that Mercury’s interior contained
sufficient volatiles to drive those eruptions. For the Moon, a pyroclastic origin has also been postulated
for some deposits, 15 with similar implications for volatile content and release. 16 And, there is a tantalizing
hint that a few areas of the Moon have recently released gases. 17
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