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

Future Directions for Investigations and Measurements
Fundamental models of volatile delivery and loss relevant for understanding how processes
external to a planet can enable or thwart life and prebiotic chemistry can be constrained by investigation
of loss rates of volatiles from planets to interplanetary space, in terms of solar intensity, gravity, magnetic
field environment, and atmospheric composition. Also key are to characterize volatile reservoirs that feed
volatiles onto terrestrial planets after the main phases of planetary accretion (e.g., a late chondritic veneer,
heavy bombardment) and to evaluate impact intensity and meteoritic and cometary fluxes to the terrestrial
planets through time, including calibration of the lunar impact record.
UNDERSTAND THE PROCESSES THAT CONTROL CLIMATE IN ORDER TO CONSTRAIN
BOTH LONG-TERM CLIMATE EVOLUTION ON TERRESTRIAL PLANETS AND SHORT-
TERM NATURAL AND ANTHROPOGENIC FORCINGS ON EARTH
Terrestrial life and human civilizations have been profoundly affected by climate and climate
change. To understand and predict climate variations, one must understand many aspects of planetary
evolution on different timescales. Critical issues include the variation of terrestrial climate over geologic
timescales, the causes of extreme climate excursions (e.g., snowball Earths and the Paleocene/Eocene
Thermal Maximum approximately 55 million years ago), understanding the stability of our current
climate, and clarifying the effects of anthropogenic perturbations. This goal is closely aligned with other
NASA efforts, especially in Earth science. A key tenet is that detailed exploration and intercomparisons
of the inner planets contribute significantly to understanding the factors that affect Earth’s climate—past,
present, and future.
Fundamental objectives on the path to understand the processes that control climate in order to
constrain both long term climate evolution on terrestrial planets and short term natural and anthropogenic
forcings on Earth include the following:
• Determine how solar energy drives atmospheric circulation, cloud formation and chemical
cycles that define the current climate on terrestrial planets;
• Characterize the record of and mechanisms for climate evolution on Venus, with the goal of
understanding climate change on terrestrial planets, including anthropogenic forcings on Earth;
• Constrain ancient climates on Venus, and search for clues into early terrestrial planet
environments so as to understand the initial conditions and long-term fate of Earth’s climate.
Subsequent sections examine each of these objectives in turn, identify critical questions to be
addressed and future investigations and measurements that could provide answers.
Determine How Solar Energy Drives Atmospheric Circulation, Cloud Formation
and Chemical Cycles that Define the Modern Climate Balance on Terrestrial Planets
Results from Venus Express show that Venus’s atmosphere is highly dynamic with abundant
lightning, unexpected atmospheric waves, and aurora and nightglows that respond to high altitude global
winds. Venus Express has also found evidence of relatively recent volcanism, in a geographical
correlation of low near-infrared emissivity with geological hot-spot volcanoes. 12 These observations
support the model that Venus’s current climate is maintained, at least in part, by volcanic emission of
sulfur dioxide that feeds the global clouds of sulfuric acid. These inferences confirm that some climate
processes on Venus are similar to those on Earth, and that a better understanding of Venus’s climate
system will improve our understanding of Earth’s, and provide real-world tests of computer codes—
general circulation models (GCMs)—that attempt to replicate climate systems.
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
5-11