THE NATIONAL ACADEMIES
Advisers to the Nation on Science, Engineering, and Medicine
February 11, 2005
Mr. Alphonso V. Diaz
Associate Administrator for Science
Science Mission Directorate
Washington, DC 20546-0001
Dr. Michael S. Turner
Mathematical and Physical Sciences
National Science Foundation
4201 Wilson Boulevard
Arlington, Virginia 22230
Dear Mr. Diaz and Dr. Turner:
Over the course of the past year the National Research Council’s Committee on Astronomy and Astrophysics (CAA) and its parent organizations, the Board on Physics and Astronomy (BPA) and the Space Studies Board (SSB), began to consider whether the overall science strategy laid out in Astronomy and Astrophysics in the New Millennium (AANM) and supplemented by Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century1 is on course or should be reexamined. This discussion was prompted by the substantial programmatic changes at NASA and issues raised by the Connecting Quarks with the Cosmos report, and then grew to include the scientific and technological breakthroughs made since AANM was released in 2000. Following consultations with NASA and National Science Foundation officials, the NRC decided to convene a committee with the following charge:
An NRC committee will prepare a short report reviewing the scientific discoveries and technical advances in astronomy and astrophysics over the 5 years since the publication of the decadal survey, Astronomy and Astrophysics in the New Millennium (AANM). It will address the implications of scientific and technical developments as well as changes in the federal program. It will assess progress toward realizing the vision for the field articulated in AANM and supplemented by Connecting Quarks with the Cosmos.2
This letter report presents the conclusions and recommendations of the Committee to Assess Progress Toward the Decadal Vision in Astronomy and Astrophysics. The judgments it reflects are based on the deliberations and experience of the committee and on information obtained in discussions with agency officials at the committee’s meeting on October 23-24, 2004, at the Keck Center of the National Academies in Washington, D.C.3 The committee included some current members of the CAA, BPA, and SSB, as well as some members of the Astronomy
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine 500 Fifth Street, NW Washington, DC 20001 Phone: 202 334 3520 Fax: 202 334 3575 E-mail: email@example.com www.nationalacademies.org/bpa February 11, 2005 Mr. Alphonso V. Diaz Associate Administrator for Science Science Mission Directorate NASA Headquarters Washington, DC 20546-0001 Dr. Michael S. Turner Assistant Director Mathematical and Physical Sciences National Science Foundation 4201 Wilson Boulevard Arlington, Virginia 22230 Dear Mr. Diaz and Dr. Turner: Over the course of the past year the National Research Council’s Committee on Astronomy and Astrophysics (CAA) and its parent organizations, the Board on Physics and Astronomy (BPA) and the Space Studies Board (SSB), began to consider whether the overall science strategy laid out in Astronomy and Astrophysics in the New Millennium (AANM) and supplemented by Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century1 is on course or should be reexamined. This discussion was prompted by the substantial programmatic changes at NASA and issues raised by the Connecting Quarks with the Cosmos report, and then grew to include the scientific and technological breakthroughs made since AANM was released in 2000. Following consultations with NASA and National Science Foundation officials, the NRC decided to convene a committee with the following charge: An NRC committee will prepare a short report reviewing the scientific discoveries and technical advances in astronomy and astrophysics over the 5 years since the publication of the decadal survey, Astronomy and Astrophysics in the New Millennium (AANM). It will address the implications of scientific and technical developments as well as changes in the federal program. It will assess progress toward realizing the vision for the field articulated in AANM and supplemented by Connecting Quarks with the Cosmos.2 This letter report presents the conclusions and recommendations of the Committee to Assess Progress Toward the Decadal Vision in Astronomy and Astrophysics. The judgments it reflects are based on the deliberations and experience of the committee and on information obtained in discussions with agency officials at the committee’s meeting on October 23-24, 2004, at the Keck Center of the National Academies in Washington, D.C.3 The committee included some current members of the CAA, BPA, and SSB, as well as some members of the Astronomy 1 The two reports were published by the National Academies Press, Washington, D.C., in 2001 and 2003, respectively. 2 Appendix A gives a short overview of the vision of the field articulated by the two reports. 3 Appendix B gives the roster of the committee and the agenda of the committee meeting.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report and Astrophysics Survey Committee (which produced the AANM report) and Committee on the Physics of the Universe (which produced Connecting Quarks with the Cosmos). The committee’s response to its charge focuses on four broad topics: A summary of the context and programmatic changes that led to the initiation of this letter; An overview of the most exciting advances in astronomy and astrophysics since the AANM report was completed; An overview of some of the technological developments that are leading to the next generation of instruments and capabilities; and An assessment of the progress that has been made toward realizing the decadal vision, and potential opportunities and obstacles on the path to fulfilling that vision. I. CONTEXT FOR THE COMMITTEE’S DELIBERATIONS The most recent in a series of survey reports in which the community has reached consensus on an integrated list of priorities for the coming decade,4 Astronomy and Astrophysics in the New Millennium (AANM) was the culmination of a 2-year process of information collection and synthesis involving the broad astronomy and astrophysics community. This process is widely recognized as the gold standard for science priority setting and, over the past 50 years, has played a significant role in enabling the tremendous successes of the nation’s astronomy and astrophysics research enterprise. Since the AANM report was released in the spring of 2000, astronomy and astrophysics has continued to be an exciting and very rapidly evolving area of transformative research. We now know, with considerable precision, that the universe is nearly 14 billion years old and filled with a mysterious form of energy. We know that planets around other stars are fairly common objects in our galaxy, and we expect that planets like our own will be discovered one day. We know that immense black holes, millions of times as massive as our Sun, grow at the center of galaxies as those galaxies form. These and other remarkable advances in understanding the workings and content of the universe have enriched the nation and the world. These profound discoveries have been paralleled, and in many cases enabled, by an ongoing technological revolution in astronomical instrumentation and facilities, which has provided researchers with a suite of new tools for exploring the universe that remains beyond our physical reach. Further, the continued explosion of computational power and theoretical work has enabled exploration of phenomena at the limit of human understanding. With these advances, new opportunities for discovery have arisen. One example is the recent confirmation that the universe is not just expanding, but is doing so at an increasing rate. Evidence of dark energy was discovered as the Astronomy and Astrophysics Survey Committee was beginning its deliberations, and it was independently confirmed only in the years after the release of the AANM report. This discovery had immediate and profound implications for fundamental physics, which a broad-based coalition of astronomers and physicists are working to understand. This scientific frontier and others at the interface of physics and astronomy were discussed in Connecting Quarks with the Cosmos. To their credit, the federal agencies that support astronomy and astrophysics research have responded quickly to these new discoveries at the intersection of physics and astronomy, as described in the Office of Science and Technology Policy’s report The Physics of the Universe5 and in NASA’s Beyond Einstein roadmap.6 4 The five reports are Astronomy and Astrophysics in the New Millennium, NRC, 2001; The Decade of Discovery in Astronomy and Astrophysics, NRC, 1991; Astronomy and Astrophysics for the 1980’s, NRC, 1982; Astronomy and Astrophysics for the 1970’s, NRC, 1972; and Ground-based Astronomy: A Ten Year Program, NRC, 1964. 5 Office of Science and Technology Policy, The Physics of the Universe, OSTP, Washington, D.C., 2004.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report Scientific research proceeds in a broad context that includes the evolving circumstances of the nation, and FY 2005 presents a considerably different fiscal picture than did FY 2000. A new presidential vision for exploration,7 together with the loss of the space shuttle Columbia, continues to generate programmatic changes at NASA, while at the National Science Foundation (NSF) a new focus on strategic planning will change the way that major programs are carried out. At the same time the Department of Energy (DOE) has greatly increased its support of astronomy and astrophysics research. These shifts in federal policy have already affected the astronomy and astrophysics research enterprise. II. NEWEST ASTRONOMICAL DISCOVERIES CHANGE OUR VIEW OF THE COSMOS The profusion of new telescopes and observatories in the 1990s generated a revolution in astronomy and astrophysics. Yet the rate of discovery in the past 5 years has exceeded even that incredible pace, so that significant progress has already been made on the fundamental questions for the decade laid out in the AANM report. New discoveries about the universe abound, extending from the moment of its creation through the formation of stars and galaxies to the Sun and Earth today. These new insights address our place in the cosmos and how it came to be, and as such are enduring contributions to our civilization. Described below are just a few examples of post-AANM discoveries in astronomy and astrophysics, organized in three broad themes: The universe and the nature of matter and energy, Our place in the cosmos, and The formation and evolution of black holes. The Age of the Universe, the History of Its Expansion, and the Nature of Matter and Energy Dark Energy and Fundamental Physics Studies of distant supernovae, from the ground and with the Hubble Space Telescope (HST),8 have now shown that the cosmic expansion of the universe is accelerating, propelled by “dark energy” that is outside the realm of known physics. This phenomenon was confirmed by the WMAP satellite’s painstaking measurements of the strength and size of density fluctuations in the early universe, which yielded a precise understanding of the size and shape of space-time as a whole. It is now clear that dark energy exists and that it governs the destiny of the universe, even if its nature remains completely unknown. The planned high-priority programs from space (Einstein Probes, Con-X) and from the ground (LST, GSMT) are necessary to explore dark energy. The knowledge gained may well lead in turn to a unified understanding of fundamental forces, gravity, and space-time. Dark Matter and the Density of the Universe The large-scale structures seen in the universe today originated in quantum fluctuations smaller than a single atom at the time of the Big Bang. This theoretical picture, first established with COBE, has now been confirmed in much greater detail with WMAP observations of tiny variations in the cosmic microwave background. New computational simulations follow the growth of these variations into the large structures seen in today‘s universe—mapped in 6 National Aeronautics and Space Administration, Beyond Einstein: From the Big Bang to Black Holes, NASA, Washington, D.C., January 2003. 7 A Renewed Spirit of Discovery, the President’s Vision for U.S. Space Exploration, The White House, January 2004. 8 Missions are briefly described and acronyms defined in Appendix C.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report abundant detail with the enormous new galaxy surveys—and confirm the essential gravitational role of dark matter. The ongoing quest to identify dark matter particles involves a broad array of ground- and space-based experiments. The amount of dark matter and the properties of dark energy dictate the size and earliest emergence of the largest clusters of galaxies, which are permeated with hot gas and thus are being discovered and observed at radio and X-ray wavelengths. Chandra XRO and XMM-Newton have also shown that hot cluster gas is roiled by bubbles and jets, echoing ancient growth spurts of the supermassive black holes in galaxy nuclei within the clusters. These observations will be expanded upon by Con-X. The Dawn of the Modern Universe: The First Stars New computations have revealed that the gravitational collapse of pristine gas in the early universe leads to the formation of a first generation of unusually massive stars. When these stars explode as supernovae at the end of their lifetimes, they may leave behind black holes hundreds of times heavier than our Sun, which in turn could serve as the nuclei of forming galaxies. Recent observations by HETE-2 and INTEGRAL have established that at least some gamma-ray bursts—the most luminous events in the universe—are associated with supernovae, suggesting that primordial supernovae will be visible as gamma-ray bursts with Swift and GLAST. Ultradeep imaging with Spitzer has revealed infrared-bright objects that may be the earliest examples of accreting black holes. The earliest stars reionize the neutral gas throughout the young universe, increasing its transparency, such that WMAP has now seen the signature of this reionization in the polarization of the cosmic microwave background, and opacity in the young universe has been detected in the spectra of distant quasars. Understanding this era is a high level goal of the JWST mission. The First Galaxies and Early Star Formation New multiwavelength observations of the young universe reveal a kind of galaxy evolution very different from that in the local universe. In the young universe star formation occurred primarily in so-called submillimeter galaxies that were far more plentiful than today, with star formation rates up to 1000 times greater than in our Milky Way Galaxy. At these prodigious rates, the entire interstellar medium looked like the most extreme massive molecular clouds in our Milky Way Galaxy. AANM priority programs such as ALMA, JWST, GSMT, and EVLA will bring the formation of normal galaxies into view; so far, astronomers can observe only the rare monsters, which account for only about half of the total star/galaxy formation. The beginning of spatial clustering is also hinted at in these galaxies, allowing tests of theories of structure formation. Interestingly, current theory fails to predict the monster submillimeter galaxies seen so far: galaxy evolution—as evidenced by star formation, massive black hole formation, and galaxy assembly—appears to happen much faster than predicted by models. Improved theoretical capability and sophistication are clearly needed. Our Place in the Cosmos: the Formation of Stars and Planetary Systems, and the Sun’s Effect on Earth Planets Around Other Stars In the last 5 years the number of known planets around other stars has increased 10-fold. Most were found via the wobble induced in the star they orbit, which favors the detection of heavy planets in orbits close to the star. Thus most planetary systems discovered so far are quite different from our own solar system. With more precise measurements and with new techniques, smaller and smaller planets are starting to be found, a critical step toward realizing the compelling goal of finding planets similar to Earth—i.e., habitable planets. TPF, highlighted by the AANM report for completion in the next decade, is dedicated to finding and characterizing these planets around nearby stars. Already, though, five new extrasolar planets have been found via transit
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report surveys (detecting the diminution of light as the planet crosses in front of the star) and one by gravitational microlensing (detecting the effect of the bending of stellar light by the gravity of the planet). Physical characteristics of a handful of planets have been measured, including radii and absolute masses or mass limits. Understanding of their atmospheres has been strengthened by a groundbreaking HST measurement of atmospheric sodium and atomic hydrogen in one of the transiting planets. The growing numbers of planets discovered, the detection of new kinds of planets, and the measurement of their physical characteristics raise many questions regarding the origin of planetary systems and point to the need for further theoretical work on planet formation, migration, and evolution. Planetary Formation Researchers are learning rapidly about the origins of planetary systems. New Spitzer images show that disks around young stars are replenished stochastically, probably in large collisions that are part of the planet-building process. Gaps, rings, and clumps in disk material reveal the location of forming planets. Recent HST and ground-based observations of debris disks around several stars have shown clear evidence of small planetary building blocks. Hundreds of newly discovered brown dwarfs raise new questions about low-mass star formation and Jupiter-mass planet formation. The diversity of planetary systems is dramatic and argues for extensive future surveys and a strong parallel effort in theory. Solar System Formation The formation and early evolution of our own solar system is recorded in the fossil record of material and debris contained within the Kuiper Belt, a ring or disk of material circling the Sun beyond the orbit of Neptune. The recent discovery of new large objects far beyond Pluto’s orbit has led to studies of their surface composition and physical properties, and indicates the discovery potential of the AANM report’s priorities like LST and GSMT. Characterization of the icy surfaces of these bodies will offer clues to the processes occurring in the circumstellar disks now being studied around other stars. The first Neptune Trojan satellite (a small asteroid in a resonant orbit with Neptune and the Sun) was just found (compared to ~1560 known Jupiter Trojans), which augers well for progress in understanding the formation of giant planets. Detailed observations of the solar system provide crucial clues to understanding the origins and evolution of this and other planetary systems. The Physics of the Sun and Its Effect on Our World Accurate measurements of the flux of solar neutrinos confirmed definitively the oscillation of one kind of neutrino into another. Common neutrinos must have small but finite mass, and new theories will be required. Abundances of elements heavier than hydrogen or helium in the Sun appear to be 25 percent lower than previously thought, which will have a major impact on our understanding of the internal structure of the Sun and other stars. For the first time RHESSI gamma-ray images show ions accelerated by solar flares and, surprisingly, indicate that they are not where the accelerated electrons are, but instead are 10,000 to 15,000 kilometers away. These effects, which can be studied in detail on the Sun, offer clues to the extremely energetic environments of black holes and neutron stars. An array of satellites that accurately monitors space weather is rapidly improving understanding of the Sun’s effects on the developing Earth and on current space activities. Observations of the Sun at several length scales and wavelengths show that the emergence of small-scale magnetic fields all over the solar surface can transfer mass and energy to larger-scale magnetic structures, energizing the corona and occasionally leading to coronal mass ejections that have a powerful impact on Earth’s magnetosphere. Future priority projects of the AANM report, such as ATST and SDO, will explore this complex global picture.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report Our Galaxy’s Supermassive Black Hole and Star Formation Precision astrometry of stars at the center of our Milky Way Galaxy has revealed the presence of a black hole several million times the mass of our Sun—the first, closest, and most definite black hole known. Recent speckle and adaptive optics measurements of stars orbiting close to the black hole give constraints on its mass, including direct measurements of the accelerations caused by the black hole’s strong gravitational pull. Surprisingly, some of the stars that pass extremely close to the black hole are very young, yet the turbulent conditions in the galactic center would seem to preclude the recent collapse of cold gas to form stars. How and where these stars formed is an unexpected mystery with profound implications for our understanding of star formation as well as physical conditions near supermassive black holes. The Formation and Evolution of Black Holes and Probing Strong Gravity and High Densities Solving the Mystery of the X-ray Background One of the oldest puzzles in extragalactic astronomy is the origin of the luminous all-sky X radiation discovered about the same time as the cosmic microwave background. Chandra and XMM-Newton have now shown that the X-rays come from millions of massive black holes, many of which accrete so much gas that they are invisible optically. In new deep surveys their host galaxies have been detected with HST, allowing researchers to determine their locations and ages, and Spitzer has detected the energy re-radiated from the X-ray-heated accreting gas, confirming the strongest prediction of this picture and providing a quantitative measure of the total mass accreted onto black holes. Deeply hidden black holes not yet detected will be mapped throughout the cosmos with future AANM priority missions like EXIST or an equivalent Black Hole Finder Probe.9 Supermassive Black Holes in Galaxy Nuclei Discoveries made in the 1990s showed that virtually every galaxy has at its center a supermassive black hole, and we know that the black hole has a mass proportional to the mass of stars in the bulge of the host galaxy, implying a physical connection between the formation of galaxies and the growth of supermassive black holes. Spitzer and HST will directly observe this physical connection, observations with GSMT and JWST will shed light on the origin of the correlation, and observations with Con-X will provide information on processes occurring just outside the black hole horizon. LISA will reveal mergers between supermassive black holes in the early universe, as their host galaxies merge. Exploring Curved Space-Time Around Spinning Black Holes Almost a century ago, Albert Einstein’s general theory of relativity predicted the existence and properties of black holes. Now for the first time the theory is being tested quantitatively in the strong-field limit, with X-ray spectroscopy of hot iron ions orbiting close to the black hole horizon. Apparently the black holes in active galaxies and binary stars rotate very rapidly, and the rotation provides the energy needed to generate the highest-energy emission from these objects. LISA will map out space-time using gravitational radiation emitted by orbiting stars, and Con-X will use much finer resolution X-ray spectroscopy to trace the motion of the gas in detail. 9 The AANM report recommended the EXIST mission, which has since been folded into the Beyond Einstein program as a candidate for the Black Hole Finder Probe.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report Neutron Star Laboratories for Precision Tests of General Relativity and Physics at High Densities The remarkable discovery of a double radio pulsar provides a new laboratory for general relativity, stellar evolution, and magnetospheric physics. The tight 2.5-hour orbit and its edge-on inclination have led to unprecedented accuracy in the two neutron star masses.10 Further monitoring will soon yield the first accurate measure of the distribution of mass within the neutron star and therefore a clearer understanding of the nuclear material that makes up these objects. X-ray spectroscopy with Chandra and XMM/Newton has resulted in the first measurement of the gravitational redshift of photons escaping the neutron star‘s strong gravity. The redshift measures the pressure exerted by material at densities exceeding that of particles in atomic nuclei. Such extreme density is not reproducible in laboratories on Earth. X-ray spectroscopy has also shown that in young neutron stars atoms are dramatically distorted by magnetic fields whose strength is in excess of a trillion times that of Earth’s magnetic field, and has yielded the first secure measurements of the range of rates at which young neutron stars cool. The cooling rate in turn indicates the rate of neutrino emission in neutron star cores, another probe of nuclear physics at extreme density and temperature. An explosion of advances in this science will come with the greater sensitivity of Con-X. III. TECHNOLOGICAL ADVANCES THAT TRANSFORM OUR EXPLORATORY REACH Successful implementation of the missions and facilities envisioned in the AANM report requires a timely and sustained commitment to technology development. Since the survey was released in early 2000, progress has been made in a number of areas, highlights of which are listed below, (with the projects which will benefit): Adaptive optics for diffraction-limited performance of large ground-based telescopes and for sensitive optical interferometry (GSMT, ATST); Large-format, low-noise, broadband infrared detectors and low-emissivity mirror coatings (JWST, SAFIR); Gigapixel low-noise optical/infrared charge-coupled device (CCD) cameras for surveys (LST); Manufacture and alignment of lightweight X-ray optics and improvements in X-ray detectors (Con-X, EXIST/Black Hole Finder Probe); Bolometric arrays that will enable the next generation of cosmic microwave background experiments (Einstein Inflation Probe); Spacecraft ranging and formation flying techniques for space-based arrays (LISA, TPF); Digital signal processing driving new receiver, correlator, and antenna array designs (SKA, LOFAR, FASR); Information technology for large (tera/petabyte) archives linking multi-wavelength data from many instruments and facilities (NVO, LST); Starlight suppression techniques for high dynamic range imaging (TPF); and TSIP initiatives that are providing new observational capabilities within the broad system of U.S. ground-based assets. It is the view of the committee that these advances in technology have occurred at a pace commensurate with the timely implementation of the AANM report priorities—although a steady, predictable resource stream will be necessary to maintain this progress. For the missions 10 Pulsars are a form of neutron star.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report and facilities still under development, the choice of technology will be evaluated as part of the planning process leading to implementation. This committee sees no technological breakthroughs or challenges that require detailed further assessment or that imperil achievement of the AANM decadal vision.11 New technologies may well arise as part of the new exploration vision, in which case the timing will be optimal for their being fed into the next decadal survey. One significant and pressing concern is the effect of ongoing programmatic changes on the young investigators who are developing the technological breakthroughs that ensure the future of astronomy and astrophysics, as well as developing new theories and planning and implementing the needed observational programs. Talented students are strongly attracted to astronomy and astrophysics but are hesitant in the current uncertain climate to commit their future careers to the field. Instrument builders are particularly critical to the health of the field. Without the next generation of instrumentalists, practical knowledge about how to work in endangered technical areas (such as high-energy astrophysics) will be lost, greatly reducing the probability of success and diminishing U.S. leadership. Human capital may be the greatest challenge facing the astronomy profession today, which is why a stable strategic plan is so vital to the astronomy and astrophysics enterprise. IV. THE OUTLOOK FOR FULFILLING THE DECADAL VISION Looking forward, how do we explore the universe? How do we directly probe its origin? What are the properties of the dark matter and dark energy that now dominate the universe? How did stars and galaxies form and evolve? Powerful clues to the answers to these fundamental questions are imprinted on the spatial patterns of the glow from the Big Bang—the cosmic microwave background radiation—the universe’s expansion, and the structure of clusters of galaxies. The AANM and Beyond Einstein reports provide a well-integrated and coherent program to advance these frontiers of discovery. Using JWST, GSMT, LST, Con-X, and the Einstein Probes, researchers will make observations of supernovae at vast distances to illuminate the expansion history of the universe, observe cosmic structure and clusters of galaxies to expose the growth of structure of the universe, and provide detailed views of galaxies and stars from their birth to today. We can expect to be further astonished—either at the success of our current models in accommodating the rich new datasets, or at the new insights that will inevitably flow from the new questions they raise. The remarkable advances in understanding in astronomy and astrophysics achieved over the past 5 years do not require that the NRC reexamine the AANM report or undertake an in-depth mid-course review of the scientific goals or recommended priorities. On the contrary, progress in the field validates the broad scientific program envisioned by the survey and implemented thus far by the agencies. That said, the committee is concerned that the careful balance that is crucial to the field be maintained. Balance across the various subdisciplines is particularly critical in astronomy and astrophysics. Unlike laboratory scientists who can arrange and establish controlled conditions for exploring a phenomenon, astronomers must search for and observe events in the natural world to advance understanding. The role of serendipity is therefore greater than in more closely controlled laboratory sciences. The most exciting scientific discoveries from new instruments are often not anticipated, and astronomers and astrophysicists must design their programs to provide the flexibility necessary to explore unforeseen phenomena. The success of the programs 11 Advances in new coronagraphic instruments have led NASA to accelerate a coronagraphic TPF mission. The letter report of the NRC’s Panel to Review the Science Requirements for the Terrestrial Planet Finder (2004) comments further on advances in coronagraphy and the potential need for an independent review of the new capability. That letter can be found at http://books.nap.edu/catalog/11105.html.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report recommended in the astronomy and astrophysics decadal surveys over the past 50 years attests to the wisdom of a balanced approach.12 The suite of projects recommended in the AANM report provides the flexibility to explore the universe across a wide range of conditions. A broad portfolio of activities is a powerful tool for exploration. For example, the confirmation that supermassive black holes lie at the heart of galaxies—including our own—resulted from Chandra, HST, Spitzer, and ground-based telescope observations. The combination of HST and ground-based studies of supernovae yielded the first hint of dark energy and the accelerating expansion of the universe, confirmed shortly thereafter by WMAP observations of the cosmic microwave background and now being constrained in an independent way by the Chandra and XMM-Newton X-ray observatories. Completely independent observations enhance researchers’ ability to explore the properties of newly discovered phenomena, and confirmation of new discoveries using completely independent observations greatly strengthens their scientific case. In addition, there is increasing synergy among particle physics, astrophysics, and astronomy, exemplified by the discoveries regarding dark energy. Particle physicists supported by the DOE are focusing more attention and resources on what have traditionally been thought of as astrophysical questions. Recent NRC reports such as the AANM report, Connecting Quarks with the Cosmos, and U.S. Astronomy and Astrophysics: Managing an Integrated Program (by COMRAA)13 have encouraged closer interagency cooperation. The federal agencies, including the OSTP, have responded well to these reports. The formation of the federal Astronomy and Astrophysics Advisory Committee (AAAC) and recent interagency coordination efforts (e.g., as embodied in OSTP’s The Physics of the Universe) represent significant and important programmatic advances that aid the fulfillment of the decadal vision. This coordination works because of the strong planning process in the field: the astronomy and astrophysics surveys provide the strategic underpinnings for a cohesive interagency effort. While there are always changes during the period between surveys, the decadal survey process does not have to be significantly altered. In cases where specific projects change dramatically from what was described in a decadal survey, they can be reevaluated under the auspices of the CAA. This process has worked well in the past (Spitzer, JWST, SIM, and TPF are all examples).14 The NRC survey process is only the first step toward a successful program of research priorities. The agencies must then plan how to implement the priorities recommended by the survey report. The strategic planning exercises currently underway in the NSF Astronomy Division are a valuable, essential step toward the transformation necessary for managing the upcoming large projects. Also essential is identifying the necessary resources to operate and develop major new facilities. Senior reviews are valuable for periodic assessment of the allocation of resources across disciplines. Finally, detailed budget planning for the future projects recommended in a decadal survey will allow timely achievement of the high-priority science. 12 “Balance” as used here means balance among various observational techniques and facilities in the discipline of astronomy and astrophysics. 13 National Research Council, U.S. Astronomy and Astrophysics: Managing an Integrated Program, National Academy Press, Washington, D.C., 2001. 14 “On Optimum Phasing for SIRTF,” letter from SSB chair Claude R. Canizares, BPA chair David N. Schramm, and CAA co-chairs Marcia J. Rieke and Marc Davis to NASA Chief Scientist France A. Cordova, February 2, 1996. SIRTF was later renamed the Spitzer Space Telescope. “Scientific Assessment of the Descoped Mission Concept for the Next Generation Space Telescope (NGST),” letter from SSB chair John H. McElroy and BPA chair John P. Huchra to Dr. Edward J. Weiler, associate administrator for NASA’s Office of Space Science, September 24, 2001. NGST was later renamed the James Webb Space Telescope. “Review of the Redesigned Space Interferometry Mission (SIM),” letter from SSB chair John H. McElroy and BPA chair John P. Huchra to Dr. Edward Weiler, associate administrator for NASA’s Office of Space Science, September 12, 2002.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report Also, as discussed in the AANM report and Connecting Quarks with the Cosmos, future planning for astronomy and astrophysics should take into account the increasing involvement of the DOE’s Office of Science and the scientists that it supports. DOE’s external planning process as conducted by the High-Energy Physics Advisory Panel should consider DOE’s role in astronomy and astrophysics. DOE should continue to coordinate its program with NASA and the NSF; its participation in the federal AAAC is an important step. NASA has an important tradition of roadmapping and strategic planning, carried out with help from the agency’s FACA advisory committees. The most recent example, the Beyond Einstein roadmap (currently being updated), is an excellent implementation and synthesis of the AANM report and Connecting Quarks with the Cosmos. Demonstrating how agency processes can integrate new discoveries into the broad framework laid out by the decadal survey, Beyond Einstein reinforces the decadal survey’s high-priority missions Con-X and LISA, highlighting them as facility-class missions called the Einstein Great Observatories. In addition to accomplishing the specific scientific goals proposed for them in the AANM report, these observatories will provide a broad and flexible science return across all of astrophysics, as have HST, CGRO, Chandra, and Spitzer before them. As a complement to Con-X and LISA, the Beyond Einstein roadmap recommended a series of three Einstein Probes to address the following questions: How did the universe begin? (Inflation Probe) How did black holes form and grow? (Black Hole Finder Probe) What is the mysterious energy pulling the universe apart? (Dark Energy Probe).15 Implementation of these probes is to be carried out in a competitive environment designed to yield the best science. As stated in Beyond Einstein, “For these missions, the science question is defined strategically but the science approach and mission concept will be determined through peer review.” The concept of the Einstein Probes builds on the legacy of the Explorer line of missions, which have continually been endorsed in decadal surveys and which are among the most successful, most cost-effective of NASA’s programs. The role of these missions has been to allow NASA to respond to a new scientific discovery without waiting for the next decadal survey. The open, competitive nature of these projects ensures that the best science is done and adds to the vitality of the field. In recent budget cycles, however, the entire program outlined in Beyond Einstein has been delayed while NASA responded to other concerns. For the program to fulfill its promise, support for the Beyond Einstein projects needs to be sustained. This is especially important for projects that are underway, in order to maintain continuity in research expertise. Among the AANM survey’s recommended ways to enhance the impact and value of theoretical astrophysics, some, notably support for postdoctoral associates and for theory associated with current missions such as Chandra, HST, and Spitzer, have been important changes from previous agency practice. NSF’s institution of a postdoctoral fellowship program open to theorists and the real growth in the individual grants program have been positive responses. However, the primary recommendation regarding theory has not yet been implemented, namely that theory challenges be integrated into most moderate or major new initiatives so as to encourage theorists to contribute to mission design and the interpretation and understanding of mission results. No theory challenges are explicitly implemented in any of the AANM-recommended initiatives now underway, potentially inhibiting the synergy envisioned by the AANM survey committee, which advocated the kind of broad, visionary theory program that enhances the discovery potential of future missions. Looming on the horizon is the critical question of the future of HST. As this report was 15 National Aeronautics and Space Administration, Beyond Einstein: From the Big Bang to Black Holes, NASA, Washington, D.C., January 2003, pp. 15-16.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report being prepared, one of the most important instruments on HST, the Space Telescope Imaging Spectrograph, failed, and the Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope released its report on various options for servicing the satellite.16 This committee agrees with the report’s conclusions, which state that the past science accomplishments of HST are considerable and that the future promise of an extended mission, with the new COS ultraviolet spectrometer and the WF3 large-format optical-infrared camera, is unquestionably exciting and of immense value. The report also states that the only effective means of servicing HST is a shuttle servicing mission. The future of the Hubble Space Telescope is being debated in political circles. As of this writing it seems possible that HST will be serviced either robotically or with the shuttle, or that it will be de-orbited rather than serviced, or that an alternative platform will be launched with COS, WF3, and possibly an additional instrument aboard. In the absence of a clearer picture, this committee’s advice is necessarily general. First, although the AANM report assumed that HST would be kept operating until 2010, it is the judgment of this committee that the AANM report’s recommended priorities should form the basis of the nation’s program in astronomy and astrophysics even if HST ceases operation. Second, if the cost of repairing HST or developing a fast-track HST replacement is large enough to threaten the timely completion of a substantial fraction of the projects recommended in the AANM report and Connecting Quarks with the Cosmos, then the scientific community should be involved in assessing the relative value of HST or its replacement vis-à-vis the affected program. It is vital that the strong, balanced science program in astronomy and astrophysics that has served the nation so well continue to be sustained as any new policy is implemented. The new exploration initiative at NASA has brought a welcome new purpose to the human spaceflight side of the agency and has provided some new opportunities for selected areas of the science program. The long-term impact on astronomy and astrophysics is not entirely clear, but short-term changes are already having an effect, and there are community concerns that serious problems lie ahead. NASA’s Science Mission Directorate has chosen to advance the design and construction of a new telescope designed to accomplish the goals of the Terrestrial Planet Finder mission.17 This decision appears to be contributing to the delays to the Beyond Einstein projects mentioned above. The committee is very concerned that these selective impacts will adversely affect NASA’s ability to generate the kind of transformative science that is the hallmark of the past decades. The Aldridge commission’s notional science agenda18 for implementing the new exploration vision includes the scientific goals articulated in the Beyond Einstein roadmap. The committee believes that maintaining the breadth of the astronomy and astrophysics enterprise at NASA is consistent with the new exploration vision. Agencies need to move aggressively to advance areas that are ripe for discovery. Still, even the most exciting science has to proceed in a way that takes into account necessary precursor science and critical challenges in technology development. The new exploration initiative will surely open unanticipated opportunities that will have to be evaluated and folded into the next decadal survey process. A well-planned, carefully considered strategy will ensure that the nation’s valuable resources are used optimally to meet its highest-priority scientific goals. The peer review basic to the decadal survey process of prioritization and to the selection process for 16 National Research Council, Assessment of Options to Extend the Life of the Hubble Space Telescope: Final Report (released December 8, 2004, as a prepublication, available at http://books.nap.edu/catalog/11169.html), The National Academies Press, Washington, D.C., forthcoming. 17 The TPF letter report (cited above) requested by NASA reviews this decision. The letter recommends that NASA conduct an independent technical assessment of the TPF-C project, and it expresses reservations about the process by which the decision was made to advance TPF-C. The letter can be found at http://books.nap.edu/catalog/11105.html. 18 President’s Commission on Implementation of U.S. Space Exploration Policy, A Journey to Inspire, Innovate, and Discover, GPO, Washington, D.C., 2004.
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Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision: Letter Report mission lines like Explorers and the Einstein Probes helps to ensure the critical examination essential to developing a successful national program. The committee and the community it represents value immensely the ongoing dialog between the astronomy and astrophysics community and the agencies. The process whereby the community assesses scientific priorities in decadal surveys and the agencies implement the vision articulated in these surveys, taking into account the practicalities of technology readiness and the realities of programmatic concerns, has served both the scientific community and the U.S. public well for many years. It is this committee’s assessment that progress toward the strategy articulated in the AANM and Connecting Quarks with the Cosmos reports underscores the continuing success and vitality of the strategy. As long as the necessary breadth and balance are maintained in the current scientific program for astronomy and astrophysics, prospects for an unprecedented decade of discovery are indeed bright. Sincerely, /s/ C. Megan Urry, Chair Committee to Review Progress in Astronomy and Astrophysics Toward the Decadal Vision cc: Ghassem Asrar, Deputy Associate Administrator, Science Mission Directorate, NASA Anne L. Kinney, Director, Universe Division, NASA G. Wayne Van Citters, Director, Astronomy Division, NSF Robin Staffin, Director, Office of High Energy Physics, DOE Charles Elachi, Director of Advanced Planning, NASA Burton Richter, Chair, Board on Physics and Astronomy Lennard A. Fisk, Chair, Space Studies Board Donald C. Shapero, Director, Board on Physics and Astronomy Joseph K. Alexander, Director, Space Studies Board