To illustrate the role of the decadal surveys in identifying the top-priority scientific questions for the future,4 the committee points out that Astronomy and Astrophysics for the New Millennium lists a set of five major scientific objectives to be addressed in the first decade of the 21st century. These include, “Determine the large-scale properties of the universe: the amount, distribution, and nature of its matter and energy, its age, and the history of its expansion,” and “understand the formation and evolution of black holes of all sizes” (p. 3). New Frontiers in the Solar System presents 12 key scientific questions that fit within four crosscutting themes. The questions include, How did the impactor flux decay in the early solar system, and how did this affect the timing of life’s emergence on Earth? What planetary processes generate and sustain habitable worlds, and where are the habitable zones in the solar system?, and, What hazards do solar system objects present to Earth's biosphere? (p. 3).

In a similar manner, the priorities presented in the solar and space physics survey, The Sun to the Earth—and Beyond, were narrowed to eight scientific questions, including, “What is the nature of the interstellar medium, and how does the heliosphere interact with it?” and “How does Earth’s global space environment respond to solar variations?” (p. 2). Likewise, Connecting Quarks with the Cosmos posed 11 fundamental questions, including, “What is dark matter? What is the nature of dark energy?” and, “How did the universe begin?” (p. 2).

In setting priorities among an array of recommended missions, the capacity to address these kinds of questions was an explicit criterion. For example, the judgments on the scientific merit of competing mission concepts reflected in New Frontiers in the Solar System were made on the basis of how missions could provide new knowledge as measured by application of the following criteria:

  • Will answering the scientific question create or change an existing scientific paradigm?

  • Might the new knowledge gained strongly direct future research?

  • Will the new knowledge gained substantially strengthen understanding?

Consequently, the committee concludes that the most recent NRC decadal surveys for the fields of astronomy and astrophysics, solar system exploration, solar and space physics, and the interface between fundamental physics and cosmology remain valid in the context of NASA’s new exploration vision because they do identify the critical science questions to be addressed in the next decade of space exploration. The committee recommends that these reports—Astronomy and Astrophysics in the New Millennium (2000), New Frontiers in the Solar System: An Integrated Exploration Strategy (2002), The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics (2002), and Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century (2003)—be used as the primary scientific starting points to guide the development of NASA’s strategic roadmaps that include these areas.

In addition, the first-of-its-kind decadal survey-style study for Earth sciences and applications from space mentioned above represents a fresh opportunity to look forward as the era of the Earth Observing System program comes to an end and to consider the implications of NASA’s exploration vision for NASA’s Earth science program. Prior to the completion of that study there will also be an opportunity to apply the criteria listed above as NASA prepares its roadmap for research to understand the Earth system.

Several other reports are particularly relevant for the critical scientific goals and priorities for research that must be conducted to enable human exploration. In the life sciences, the conclusions and


The complete sets of major scientific questions posed in the surveys are presented in Appendix A.

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