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

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Introduction to Planetary Science
How do planets form? What combination initial conditions and subsequent geologic, chemical,
and biological processes led to at least one planet becoming the abode for innumerable lifeforms? What
determines the fate of life on a planet? Such scientific enquiries reflect a basic human need to understand
who we are, where we came from, and what the future has in store for humanity. “Planetary science” is
shorthand for the broad array of scientific disciplines that collectively seek answers to these and related
questions.
THE MOTIVATIONS FOR PLANETARY SCIENCE
In the past, scientists only had one planet to study in detail. Our Earth, however, the only place
where life demonstrably exists and thrives, is a complex interwoven system of atmosphere, hydrosphere,
lithosphere, and biosphere. Today, planetary scientists can apply their knowledge to the whole solar
system, and to hundreds of worlds around other stars. By investigating planetary properties and processes
in different settings, some of them far simpler than Earth, we gain substantial advances in understanding
exactly how planets form, how the complex interplay of diverse physical and chemical processes create
the diversity of planetary environments seen in the solar system today, and how interactions between the
physical and chemical processes on at least one of those planets led to creation of conditions favoring the
origin and evolution of multifarious forms of life. These basic motivational threads will be built upon and
developed into the three principal scientific themes of this report—building new worlds, workings of
solar systems, and planetary habitats—in Chapter 3.
Current understanding of Earth’s surface and climate are constrained by studies of the physical
process operating on other worlds. The destructive role of chlorofluorocarbons in Earth’s atmosphere
was recognized by a scientist studying chemistry on Venus. Knowledge of the “greenhouse” effect, a
mechanism in the ongoing global warming on Earth, likewise came from studies of Venus. Comparative
studies of the atmospheres of Mars, Venus, and Earth yield critical insights into the evolutionary histories
of terrestrial planet atmospheres. Similarly, studies of the crater-pocked surface of the Moon led to
current understanding of the key role played by impacts in shaping planetary environments. The insights
derived from studies of lunar craters led to the realization that destructive impacts have wreaked havoc on
Earth in the distant past, and as recently as 100 years ago, a devastating blast in Siberia leveled trees over
an area the size of metropolitan Washington DC. Three recent impacts on Jupiter provide our best
laboratory for studying the mechanics of such biosphere-disrupting events. Wind-driven processes that
shape Earth’s desert dunes operate on Mars and even on Saturn’s moon Titan.
Planetary science transcends national boundaries. Even during the depths of the Cold War,
planetary scientists from both east and west frequently cooperated, by exchanging samples from their
respective lunar missions or by coordinating their independent missions to Halley’s Comet. Now,
decades later, planetary science is a truly global endeavor. Spacecraft that explore the planets come not
only from the United States, but also from China, India, Japan, and the nations of Western Europe. If we
expand the list to include nations with some space-based capacity—those that use spacecraft data, build
spacecraft instruments, operate relevant ground-based facilities, or contribute in some other way to the
advancement of planetary science—planetary science encompasses the globe.
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
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