panels are more representative of their parent community than their parent survey committee because they reach more deeply into their respective scientific communities.

Dressler stated that program prioritization is the heart of the decadal process. Contrary to the views of presenters in the previous session, Dressler does not think it is possible to strictly prioritize diverse scientific activities without reference to the means by which those priorities might be implemented. He illustrated his point by referencing his experience as chair of one of the 2010 astronomy and astrophysics decadal survey’s program prioritization panels (PPPs). The five science frontiers panels (SFPs) reviewed some 100 white papers solicited from the astronomy and astrophysics community. After many months of effort, each SFP prioritized the science in their respective subdiscipline and identified four key questions—for example, What determines star formation rates and stellar masses? How do rotation and magnetic fields affect stars? What are the flows of matter and energy in the circumgalactic region? How do cosmic structures form and evolve? and How did the universe begin? There is no way, Dressler contended, that any group could rank these questions from diverse subdisciplines in priority order. Even within a single subdiscipline it is difficult, if not impossible, to rank science priorities without reference to the means by which that priority might be addressed.

Dressler’s final remarks concerned the questions that should be addressed in ranking scientific and mission-related issues. Of myriad questions, science-related questions consider whether the science is

• Transformational science or incremental science?

• A fundamental physics measurement?

• Of interest to the general public?

• Broad science with a focus?

• Along a path of scientific investigation that has great future promise?

Mission-related questions consider whether the mission is

• Technically feasible?

• Mature technology, or requiring further development?

• Technology useful outside of astronomy?

• Straightforward or complex, with irreducible risk?

• Strong educational and public outreach component?

• Ready to go sooner rather than later?

• A bargain, of moderate cost, or killer expensive?

• International collaboration or going it alone?

• Along a path of technological development that is valuable for future missions?

PANEL DISCUSSION

During their discussion, the moderator and panelists talked about their experience with and opinions on the following topics:

• Science goals,

• Source of program and prioritization criteria, and

• NASA’s perspective.



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