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Introduction

The second half of the 20th century brought breakthroughs in astronomy and astrophysics made possible by a confluence of increasingly sophisticated instruments, advances in computing and information technology, new numerical tools for data processing and analysis, and powerful new theoretical insights. The limits of the observable universe now range from unimaginably large intergalactic distances down to subatomic particles, and unexpected and remarkable connections have been established between natural laws pertaining to the largest and the smallest scales.

The recent breakthroughs and potential for future advances are nothing short of revolutionary. Ten years ago the first extrasolar planets were discovered; today more than 200 are known. In our solar system, hundreds of Kuiper belt objects, a handful of trans-neptunian objects larger than Pluto, and comets with unique volatile content and mineral composition together are leading to a new understanding of our own cosmic origins. Dust and gas disks around intermediate- and low-mass stars akin to the Sun with gaps, warps, and knots detected by the Hubble Space Telescope (HST), the Spitzer Space Telescope, and large ground-based telescopes are perhaps telltale signs of active planetary system formation. Driven by these advances, in the coming years the discovery and imaging of Earth-like planets and perhaps the first evidence for life elsewhere in the universe may be realized.

Discoveries relating to the origin, evolution, and destiny of the universe have been at least as revolutionary as the discoveries made on planetary scales. The all-sky measurement of the cosmic microwave background by the Cosmic Background Explorer (COBE) satellite made an overwhelmingly compelling case for a big-bang cosmology and opened the door to studying the earliest moments of creation. The significance of the COBE breakthroughs was recognized by the



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A Performance Assessment of Nasa’s Astrophysics Program 1 Introduction The second half of the 20th century brought breakthroughs in astronomy and astrophysics made possible by a confluence of increasingly sophisticated instruments, advances in computing and information technology, new numerical tools for data processing and analysis, and powerful new theoretical insights. The limits of the observable universe now range from unimaginably large intergalactic distances down to subatomic particles, and unexpected and remarkable connections have been established between natural laws pertaining to the largest and the smallest scales. The recent breakthroughs and potential for future advances are nothing short of revolutionary. Ten years ago the first extrasolar planets were discovered; today more than 200 are known. In our solar system, hundreds of Kuiper belt objects, a handful of trans-neptunian objects larger than Pluto, and comets with unique volatile content and mineral composition together are leading to a new understanding of our own cosmic origins. Dust and gas disks around intermediate- and low-mass stars akin to the Sun with gaps, warps, and knots detected by the Hubble Space Telescope (HST), the Spitzer Space Telescope, and large ground-based telescopes are perhaps telltale signs of active planetary system formation. Driven by these advances, in the coming years the discovery and imaging of Earth-like planets and perhaps the first evidence for life elsewhere in the universe may be realized. Discoveries relating to the origin, evolution, and destiny of the universe have been at least as revolutionary as the discoveries made on planetary scales. The all-sky measurement of the cosmic microwave background by the Cosmic Background Explorer (COBE) satellite made an overwhelmingly compelling case for a big-bang cosmology and opened the door to studying the earliest moments of creation. The significance of the COBE breakthroughs was recognized by the

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A Performance Assessment of Nasa’s Astrophysics Program 2006 Nobel Prize in Physics, awarded to two COBE scientists, and the Gruber Prize in Cosmology, awarded to the entire COBE team. Results from the Wilkinson Microwave Anisotropy Probe (WMAP) Explorer mission and HST, and data from the Sloan Digital Sky Survey, a project funded in part by NASA, have pinned down the expansion rate, composition, and age of the universe and provided strong evidence that the big bang included a burst of rapid expansion known as inflation, driven by an unknown mechanism. In combination with important data from ground-based observations, these missions have enabled exploration of two profound mysteries: the attractive gravity of dark matter that holds together galaxies and larger structures in the universe, and the repulsive gravity of a new form of dark energy that causes the expansion of the universe to accelerate, rather than slow down. Together, dark matter and dark energy account for some 96 percent of the “stuff” in the universe. The nature of dark matter and dark energy and the physical cause of inflation appear to involve deep connections between the submicroscopic world and the universe at its largest scales and earliest times. Present opportunities for deepening understanding of the universe and the laws that govern it are profound. For half a century, black holes have captured the attention of scientists, science fiction writers, and the public alike. A combination of ground- and spacebased observations have now firmly established the existence of hundreds of stellar-sized black holes in our galaxy, the Milky Way, as well as a correlation between the mass of black holes at the center of a galaxy and the mass of the galaxy’s central bulge. NASA missions—including the Compton Gamma Ray Observatory (CGRO), Swift, and High Energy Transient Explorer-2 (HETE-2)—played key roles in establishing that a substantial fraction of the mysterious gamma-ray bursts, discovered 40 years ago by military satellites monitoring the nuclear test-ban treaty, are associated with the birth of black holes throughout the universe, and they occur at a rate exceeding one per day. A proposed new generation of probes will test whether or not black holes conform with the predictions of Einstein’s theory of general relativity. If there are discrepancies, analysis and interpretation of results from the probes may provide clues as to how Einstein’s theory can be modified. A large proportion of the discoveries summarized here were made using tools provided to the scientific community (and, through it, to the larger world) by U.S. taxpayers. The U.S. Congress, through the National Science Foundation (NSF), the Department of Energy (DOE), and NASA, has funded the development, construction, and use of telescopes, particle accelerators, supercomputers, and other necessary equipment. Because the financial investment was well matched to the scientific opportunities, the gains in knowledge have been enormous. This extraordinary outcome has not been merely serendipitous. In astronomy and astrophysics a system has been developed to ensure that government resources are utilized in the most effective way. Since 1964 the astronomy and astrophysics community, through the National Research Council, has produced a series of reports, known collectively as the decadal surveys, laying out priorities for federal

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A Performance Assessment of Nasa’s Astrophysics Program investment in the field. The latest such volume, Astronomy and Astrophysics in the New Millennium (AANM; National Academy Press, Washington, D.C.), was published in 2001. Comprehensive, collaborative, and broadly consultative efforts, the decadal surveys have proven highly effective in setting the agenda for scientific activities in astronomy and astrophysics in each of the last five decades. Guided largely by those surveys, NASA, through its Astrophysics Division (and precursor organizational structures), has implemented a science program whose contributions to advances in the field have been enormous. The most widely known example is the Hubble Space Telescope, which has returned unprecedented images of objects ranging from the Moon and Mars to the galaxies in the Hubble Ultra Deep Field— a collection of the most distant objects ever detected. HST, the first of NASA’s Great Observatories to be launched, was followed by the CGRO, the Chandra X-ray Observatory, and the Spitzer Space Telescope (a sensitive infrared facility). In addition to these flagship missions, NASA has built and operated numerous successful smaller missions, such as Swift, HETE-2, and WMAP, which have helped to determine the content, age, shape, and history of the universe. The current portfolio of operating missions has revolutionized the substance and the practice of astronomy and astrophysics, and NASA deserves substantial credit for their successes. The advice and priorities set out in the decadal surveys have been sound, and NASA’s implementation has been effective. In this time of continuing extraordinary discovery and stunning opportunities in astrophysics, however, NASA’s ability to forge ahead is constrained. As described in more detail in subsequent chapters, demand for increased funding for existing astrophysics programs, coupled with a less robust outlook for future budgets, is hindering the agency’s ability to achieve the goals identified in the AANM decadal survey. As is apparent in the discussion that follows, the committee believes that NASA’s effective management of its Astrophysics program is critical to realizing the great opportunities ahead to advance understanding of the universe and the place of humans within it. Chapter 2 summarizes the recommendations made in the AANM survey and the Q2C report. Chapter 3 assesses how well NASA’s plans address the goals laid out by the AANM survey and the Q2C report (addressing point one of the charge) and what progress has been made toward realizing those goals (addressing point two). In Chapter 4 the committee analyzes the factors that have led to the increased strain on the Astrophysics Division, and in Chapter 5 it recommends steps that NASA can take to optimize the science value of its Astrophysics program and its central role in enabling the discoveries and breakthroughs ahead (addressing point three). The committee concluded that the long-term structural issues in NASA’s Astrophysics program should be addressed by the next decadal survey and, in response to the final section of the charge, recommends changes to the decadal survey process intended to prevent some of the issues identified in this report from recurring in the future.