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1 Background The 2010 Astronomy and Astrophysics Decadal Survey (Astro2010) report New Worlds, New Horizons in Astronomy and Astrophysics (NWNH) recommended the Wide-Field Infrared Survey Telescope (WFIRST) as the top-ranked, space-based, large-scale activity for the coming decade. The WFIRST mission is designed to significantly advance our understanding of the origin of cosmic acceleration, to illuminate the formation and evolution of planetary systems, and to carry out powerful near-infrared surveys and conduct a guest observer program, thereby enabling a wealth of astrophysical discoveries. Soon after the release of NWNH, cost overruns and schedule delays in the James Webb Space Telescope and changes in the NASA budgets substantially reduced the anticipated funding available to NASA for new initiatives for much of the rest of the decade. The resulting cost constraints have delayed the anticipated launch date of WFIRST to the first half of the 2020 decade. During the process of the NWNH decadal survey, the European Space Agency (ESA) was considering Euclid for implementation as one of its next M(edium)-class missions. The decadal survey report mentions possible U.S. involvement with the Euclid mission in three sections: The European Space Agency (ESA) is considering an M-class proposal, called Euclid, with related goals. Collaboration on a combined mission with the United States playing a leading role should be considered so long as the committee’s recommended science program is preserved and overall cost savings result.2 Euclid is a European mission concept aimed at cosmology and dark energy, which is competing for one of two M(edium)-class launch slots, with a decision expected in late 2011 and launches scheduled for 2018 and 2019. The overlap in goals and scope between the proposed U.S. and European missions is significant, and there is potentially a grand partnering arrangement involving NASA, DOE, and ESA if the expanded scientific priorities set by Astro2010 for such a mission can be aligned among the partners, and assuming that the arrangement is consistent with the United States playing a clear leadership role.3 There have been discussions between the U.S. agencies and ESA about mounting a joint mission, which could be a positive development if it leads to timely execution of a program that fully supports all of the key science goals of WFIRST (planet microlensing, dark energy science, general investigations) and leads to savings overall. It is expected that the United States will play a leading role in this top-priority mission.4 After the publication of the decadal survey report, NASA reported results of negotiations (carried on during the decadal deliberations) with ESA for a possible 20 percent NASA contribution to the Euclid mission. The Office of Science and Technology Policy requested that the National Research Council (NRC) convene a panel to evaluate whether NASA’s Euclid proposal is consistent with achieving the priorities, goals, and recommendations, and with pursuing the science strategy, articulated in NWNH. The Panel on Implementing Recommendations from the New Worlds, New Horizons Decadal Survey (hereafter, the Implementation Panel) concluded in December 2010: 2
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A 20 percent investment in Euclid as currently envisioned and as presented by NASA is not consistent with the program, strategy, and intent of the decadal survey. NWNH stated the following if the survey’s budget assumption cannot be realized: “In the event that insufficient funds are available to carry out the recommended program, the first priority is to develop, launch, and operate WFIRST, and to implement the Explorer program and core research program recommended augmentations.” A 20 percent plan would deplete resources for the timely execution of the broader range of NWNH space-based recommendations and would significantly delay implementing the Explorer augmentation, as well as augmentations to the core activities that were elements in the survey’s recommended first tier of activities in a less optimistic budget scenario. A 20 percent contribution would also be a non-negligible fraction of the resources needed for other NWNH priorities.5 The economic and scientific landscape has changed in the year since the Implementation Panel report was released at the end of 2010. NASA announced the JWST replan during 2011. The WFIRST Science Definition Team (SDT) has spent the past year developing in greater detail a WFIRST reference mission design and characterizing its scientific potential. The SDT has presented an interim report.6 In addition the NASA proposed level of investment in Euclid, as defined by the hardware contributions under consideration, is substantially smaller than discussed in the Implementation Panel report. In October 2011, the European Space Agency selected Euclid as one of its M-class missions. At the November 7, 2011, joint meeting of the Space Studies Board and the Board on Physics and Astronomy, NASA again approached the NRC for advice regarding a potential plan for participation in the Euclid mission, at a significantly smaller level than in 2010, and asked the NRC to convene a committee to rapidly assess this plan. The NRC convened the Committee on the Assessment of a Plan for U.S. Participation in Euclid with the following statement of task: The [committee will] determine whether a proposed NASA plan for a U.S. hardware contribution to the European Space Agency (ESA) Euclid mission, in exchange for U.S. membership on the Euclid Science Team and science data access, is a viable part of an overall strategy to pursue the science goals (dark energy measurements, exoplanet detection, and infrared survey science) of the New Worlds, New Horizons report’s top-ranked, large-scale, space-based priority: the Wide Field Infrared Survey Telescope (WFIRST). This report addresses this charge and highlights several areas of opportunity as well as some concerns for the future. The next chapter reports the committee’s findings. The final chapter reports the committee’s conclusions and recommendations. The appendixes include a summary of the presentations to the committee. The committee endorses a small investment in Euclid as a first step in a strategic program that leads to implementation of the WFIRST mission. The committee finds that this contribution is consistent with the recommendations of NWNH and the conclusions of the Implementation Panel in maintaining a U.S. leadership role in dark energy studies only in combination with moving forward with the WFIRST mission’s dark energy program and its broader goals, as described in detail in this report. The current recommendation differs from the conclusion of the Implementation Panel report because the current NASA proposal, to invest modestly in Euclid, is consistent with an expeditious development of WFIRST and the achievement of the broader, and more ambitious, goals outlined in NWNH. 3