theme of PTL, a move apparently motivated by an unnecessarily narrow interpretation of the vision for space exploration. A much broader vision of NASA’s science mission in the exploration vision is described by the president’s commission’s report A Journey to Inspire, Innovate, and Discover10 and the NRC report Science in NASA’s Vision for Space Exploration.11 A February 2005 NRC letter report explicitly echoes the president’s commission that “maintaining the breadth of the astronomy and astrophysics enterprise at NASA is consistent with the new exploration vision.”12 The designation “Pathways to Life” has no previous heritage in NASA or NRC documents. The panel recommends that the nomenclature “Pathways to Life” be abandoned and that NASA develop coherent new themes in the Universe Division that will do justice to the Beyond Einstein program, the Search for Earth-like Planets program, and all the other science highlighted in the AAp decadal survey that the roadmap has agglomerated into Pathways to Life, but that represents vibrant science deserving of separate emphasis.
The current roadmap does not enunciate well all the transformative science objectives within the PTL theme and hence may not adequately follow NRC recommendations. For example, among the five fundamental questions outlined by the AAp decadal survey are, How do galaxies first arise and mature?, How are stars born and how do they live and die?, and How do planets form and change as they age? The Connecting Quarks report also lists understanding how the heavy elements were made as one of the key science questions for the new century. Dark matter is mentioned only briefly in the roadmap and gamma-ray bursts not at all, whereas these topics are significant elements of the AAp decadal survey and Connecting Quarks reports. Whether and how these areas of astrophysics are to be addressed in the NASA mission plan outlined in this roadmap are not made clear. This roadmap does not give a comprehensive PTL strategy with a well-sequenced PTL mission progression. Some areas of astrophysics (e.g., those with more tenuous connections to PTL) may thus be vulnerable to exclusion from planning in the Universe Division. The panel recommends that while maintaining appropriate objectives such as Beyond Einstein, the Search for Earth-like Planets, and other topics as distinct entities, NASA should always consider them in combination for purposes of strategic planning, technology development, and budgeting. This approach would allow a more effective statement of the science justification for the broadly capable missions and a more accurate assessment of technology needs and the costs of achieving Universe Division science objectives.
The Universe Exploration roadmap was clearly constructed with a rigorously self-imposed, narrowly focused approach, with the intention of protecting a core suite of missions within a presumed flat budget. This approach led to omission of important science objectives as outlined above and restricted discussion of missions. The panel is concerned that the circumstances under which this roadmap and the Search for Earth-like Planets roadmap were produced (pressure to align the roadmaps to a narrow view of the objectives of the vision for space exploration, changes in direction to the roadmap teams during the task, time pressure, and absence of peer review) led to some emphasis on missions that were known to NASA roadmap committee participants but that did not necessarily reflect the consensus of the AAp decadal survey. This relatively narrow focus also led to some pressure to name and describe some notional missions (e.g., the Inflation Probes) but not others in an attempt to get “in the queue.” Planning on single-decade timescales has been productive scientifically, but on longer timescales it is quite difficult to plan without knowing what will have been learned and what technologies will have become available. Therefore suggestions by the roadmap committee for missions in the far term cannot be interpreted as current community endorsement of particular missions.
The laudable strategy of preserving and supporting the Beyond Einstein mission line nevertheless marginalizes the PTL theme. All missions discussed in the roadmap in the PTL timeline are already in progress, apart from a notional “Pathways to Life Observatories” that appears two decades in the future. Beyond missions in the next decade, the roadmap balance between these two types of missions is not consistent with previous NRC recommendations. The scientific cases for the James Webb Space Telescope (JWST) and the Stratospheric Observatory for Infrared Astronomy (SOFIA) are only weakly connected to the PTL theme in the roadmap and are much more strongly articulated in the AAp survey.13