Panel Reports—New Worlds, New Horizons in Astronomy and Astrophysics (2011) / Chapter Skim
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6 Report of the Panel on Electromagnetic Observations from Space
6 Report of the Panel on Electromagnetic Observations from Space
Pages 251-310
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From page 251... ...
-- including support for scientific research and research infrastructure, advanced technology development, and scientific and technical workforce development -- are fundamentally important to NASA and to the nation."1 The Astro2010 Program Prioritization Panel on Electromagnetic Observations from Space (the EOS Panel) reviewed current astrophysics activities supported primarily by NASA's Science Mission Directorate -- specifically, those activities requiring electromagnetic observations from space as distinct from observations of particles or gravitational waves.
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From page 252... ...
The moderate/small initiatives are the SPICA/ BLISS initiative, augmentation of NASA's Explorer program for astrophysics, tech nology development for a Hubble Space Telescope (HST) successor, and augmenta tion of NASA research and analysis (R&A)
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From page 253... ...
and substantially broadened the program for this facility. In addition to two dedicated core programs -- cosmic acceleration and microlensing planet finding -- WFIRST would make large-area surveys of distant galaxies and the Milky Way galaxy, study stellar populations in nearby galaxies, and offer a guest observer program advancing a broad range of astrophysical research topics.
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From page 254... ...
Because JAXA and ESA are currently moving ahead with SPICA, the panel recommends that NASA commit to participation and begin to fund this activity now. Augmenting the Explorer Program for Astrophysics NASA's Explorer program is arguably the best value in the space astrophys ics program.
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From page 255... ...
This includes research grants in both observation and theory, as well as for laboratory astrophysics, technology development, and the Suborbital program. The panel, recognizing that these are core activities that underlie the NASA astrophysics program, recommends as urgent the augmentation of R&A funding that targets technology development and the Suborbital program.
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256 FIGURE 6.1 Astrophysics missions continuing into the 2010-2020 decade. The WISE mission, shown as under development, was launched in December 2009 and is now in operation.
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A second generation of highly capable, broad-purpose observatories is emerging. They are Fermi, the James Webb Space Telescope (JWST)
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However, progress depends equally on the ingenuity of scientists and the success of parts of the program that em phasize specific objectives, specialized capabilities, and more flexible and rapidly evolving science programs. The jewel of this approach is the Explorer program.
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3 and The Decade of Discovery in Astronomy and Astrophysics (Bahcall) .4 SCIENCE DRIVERS FOR KEY NEW FACILITIES The Science Frontiers Panels (SFPs)
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Ultralong-Duration Balloon EOS Panel acknowledges great scientific potential of these longer-duration program and Sounding programs beyond the present Suborbital program and suggests possible payload Rocket to Orbit program support from Missions of Opportunity or Explorer lines. 1991 Bahcall Surveyb Recommended Stratospheric Observatory for Under development by NASA and German Aerospace Center, DLR Telescope Infrared Astronomy (SOFIA)
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GCT-3 How do black holes grow, radiate, and influence their surroundings? GCT-4 What were the first objects to light up the universe, and when did they do it?
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The Wide-Field Infrared Survey Telescope, WFIRST, is a modest-aperture, near-IR tele scope -- the JDEM/Omega design -- that will make precise measurements of the universe's evolving geometry and structure over cosmic time. Using three powerful methods, WFIRST will lead the effort to unravel a great astrophysics mystery of our time -- why is the universe not just expanding, but expanding at an accelerat ing rate?
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From page 263... ...
The panel agrees with the conclusion of the GCT and GAN SFPs that high-resolution UV and X-ray spectroscopy are the only efficient tools for observing these baryons and studying their dynamic flows into and out of galaxies, a process that profoundly affects galaxy evolution. Both are essential: X-rays probe the hottest gas between galaxies and within galaxy clusters, while UV allows much higher spectral and spatial resolution for measuring the physical state of the gas, chemical element abundances, and microphysics.
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From page 264... ...
The PSF Panel gives special priority as a "discovery area" to the next step of characterizing planets around nearby stars, with the goal of finding planets like Earth. The panel strongly endorses this goal and recommends as its third priority an exoplanet mission to learn more about the planets of nearby stars.
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From page 265... ...
An exoplanet mission could not begin until late in the decade, so as its third priority, the panel recommends a competition between these and other possible approaches that are likely to develop over the next 5 to 10 years. The Spitzer Space Telescope made remarkable progress in studies of galaxy evolution and star formation with its astonishing sensitivity in the far infrared.
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They are essential to the health of the NASA astrophysics program. WIDE-FIELD INFRARED SURVEY TELESCOPE -- WFIRST Remarkable opportunities for new space initiatives are at hand.
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The combination of depth, area, and quality of WFIRST data in the infrared will easily surpass that of any other ground-based or space-based facility. WFIRST research bears substantially on 10 of the 20 key questions posed in the Astro2010 Science Frontiers Panel reports (see Table 6.2)
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From page 268... ...
The evidence for acceleration is itself compelling, from measurements of galaxy distances used to track the expansion and from studies of ripples in the cosmic microwave background that record the mass-energy density early in the universe's history. Whether it is dark energy, or a revision in the law of gravity, or something else altogether, these observations are telling us something new about fundamental physics.
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From page 269... ...
NASA's recently launched Kepler space telescope is up and running and looking for distant planets crossing in front of their parent stars, minutely diminishing their brightness. Kepler's survey should answer the crucial question of how common Earth-like worlds are in the "habitable" zones of the stars it is monitoring -- mostly galactic inner-disk and bulge stars.
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At what distances do they orbit their stars? In Figure 6.3 the panel shows the exoplanet discovery space of a microlensing planet search compared to those of Kepler and several ground-based techniques.
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The High Value of Near-IR Imaging from Space The sensitivity of WFIRST for near-IR imaging will be unrivaled. The requirements for a deep, multiband, infrared-imaging survey are essentially the same as those for the weak-lensing program, and so a by-product will be a spectacular, unprecedented, distant-galaxy survey with 0.2-mJy sensitivity and 0.2-arcsecond resolution over a large fraction of the sky -- a boon for studies of galaxy evolution, large-scale structure, searches for high-redshift quasars, and galactic white and brown dwarfs, just to name a few examples.
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From page 272... ...
indicates the ranges accessible with the SIM Lite mission for nearby stars. Ground-based microlensing discoveries are in red; Doppler detections are inverted "T's"; transit detections are blue squares; and timing and imaging detections are green and magenta triangles, respectively.
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From page 273... ...
The ability to resolve stellar populations of nearby galaxies -- measuring the detailed shape of the stellar giant-branch -- will provide unique information on the histories of star formation for a wide variety of galaxy types. A deep survey of the galactic halo will be the most complete study of the history of satellite-galaxy accretion by the Milky Way, and a similar study
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From page 274... ...
In addition to synergy with LSST, the surveys done by WFIRST -- large and small -- will provide high-quality source material for studies of smaller areas of the sky, in concert with ground-based telescopes such as the Thirty Meter Telescope, the Giant Magellan Telescope, and the Atacama Large Millimeter Array, and premier space facilities such as JWST and SPICA. Working with these facilities, WFIRST will play a key role in answering the wide range of questions on galaxy and cosmic evolution identified by the Astro2010 Science Frontiers Panels.
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From page 275... ...
A galactic-plane survey of one-half year, together with about 1 year allocated by open competition, would fill the initial 5-year timeline. Barring any operational problems, WFIRST should continue for another 5 years: peer review would compete augmentations of the cosmic acceleration or planet-survey programs with new or larger surveys and smaller guest observer programs.
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From page 276... ...
. Like JDEM/Omega, NIRSS is also proposed as a 1.5-m-aperture telescope, with a wide-area focal plane populated with 36 HgCdTe array detectors.
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From page 277... ...
Many future missions are likely to demand increased bandwidth, but in the case of WFIRST, this need may become urgent, especially considering the requirements of JWST and other future missions. Onboard data storage and processing, and the development of task-specific data-compression algorithms, may be required.
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From page 278... ...
Such sources include supermassive black holes at the centers of distant galaxies, hot bubbles of newly minted elements from supernova explosions, swirling gas around the neutron stars and black holes left by old supernovae, and immense clusters of galaxies. Many such X-ray sources are "invisible" -- they cannot even be seen with an ordinary optical telescope -- so X ray astronomy provides unique information that informs a wide range of cosmic questions.
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From page 279... ...
Such enhanced capability is essential for addressing many key questions in astrophysics. A more sensitive X-ray spectrometer will probe the early universe: the first clusters of galaxies and the first massive black holes.
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For example: • Does energy feedback from a supermassive black hole -- an AGN or a qua sar -- suppress star formation in its host galaxy? How does the energy pouring from supermassive black holes affect intergalactic and intracluster gas?
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rePort Panel e l e c t r o M a G n e t I c o b s e r vat I o n s sPace 281 of tHe on froM FIGURE 6.6 IXO compared to contemporary X-ray missions. IXO provides an order-of-magnitude more aperture (light-gathering power)
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The discussion is organized by the themes represented by four of the five Science Frontiers Panels of Astro2010. Galaxies Across Cosmic Time (GCT)
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Such previously unobtainable data are crucial for progress in the study of feedback. Also key to the story of galaxy evolution across cosmic time is the answer to the fundamental question, Where are the baryons?
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IXO, with its high-resolution grating, will be able to provide definitive answers as to whether this hot gas is common or rare, what is its physical state, and how it relates to the ubiquitous cooler gas seen by O VI absorption in UV light. Galactic Neighborhood (GAN)
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rePort Panel e l e c t r o M a G n e t I c o b s e r vat I o n s sPace 285 of tHe on froM Ne IX He α IXO Data, triplet Model O VIII Ly α 10 Fe XX, XXI Flux (counts s-1keV-1) Fe XVII 0.88 0.9 0.92 0.94 Energy (keV)
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From page 286... ...
Similarly, IXO's abil ity to measure the profile of the Fe K line will give the spin of a black hole of any mass, from stellar-size objects to supermassive black holes, up to billions of times the mass of the Sun.
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The panel therefore evaluated the impact on some key science programs of a 30 percent reduction in mirror area -- a substantial mass reduction -- and a spatial resolution of
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The panel believes that this level of investment is too high, given projected resources and the necessity of a balanced program. The panel therefore concluded that any needed rescoping must be done as soon as possible, with a target U.S.
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Adequate funds are essential to carry out these activities successfully. MISSIONS TO SEARCH FOR AND STUDY EXOPLANETS State of the Art There has been remarkable progress in the discovery and understanding of exoplanets in the current decade.
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From page 290... ...
This would constitute significant progress toward the PSF Panel's "discovery area" of characterizing a nearby, habitable exoplanet. Exoplanet Missions for the Next Decade Together with ground-based observations, these missions will provide signifi cant data on a wide variety of exoplanet properties, but they are just first steps toward answering important scientific questions about exoplanets.
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From page 291... ...
Since WFIRST results will improve with each succeeding campaign, there is a good chance that WFIRST will eventually succeed in measuring η⊕ over the entire range of orbital separations. FIGURE 6.13 The yield of planets anticipated from the Microlensing Planet Finder (MPF)
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From page 292... ...
Its single-pointing precision of ~10 microarcseconds or better would also allow astrometric measurements of other targets, such as massive stars, neutron stars, AGN, and other targets too faint Planets from Ida and Lin Simulations Gaia Known RV-Discovered Planets Radial Solar System Planets Velocity – 104 1 m/s 103 Planet Mass Sensitivity, M Jupiter Saturn 102 Neptune SIM Lite – Farthest Star Uranus SIM Lite – Median Star Habitable Worlds 101 for Best 60 SIM Lite Target Stars 100 Earth SIM Lite – Venus Closest Star Mars 10–1 10–2 10–1 100 101 102 Orbit Period, years FIGURE 6.14 SIM Lite planet-search-space sensitivity comparison. The red lines bracket the parameter space where SIM Lite can detect planets, a function of both orbital period and planetary mass.
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From page 293... ...
The panel agrees with the Astronomy and Astrophysics Advisory Committee's Exoplanet Task Force (ExoPTF) and the Astro2010 PSF Panel that a sub-microarcsecond astrometry mission like SIM Lite would be the current best choice for a new exoplanet mission.
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From page 294... ...
The level of zodiacal-dust emission from disks around nearby stars is an un known but crucial factor for designing planet-finding missions. Figure 6.15 is a simulated image from a 1.5-m-aperture coronagraphic space telescope of the radial velocity giant planet 47 UMa b; an exozodiacal dust disk with 3 zodis of material has been added.
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From page 295... ...
Therefore, the panel recommends a generic exoplanet mission as its third priority, after WFIRST and IXO, but leaves this choice to later judgment. Any of the missions briefly described here will make good progress toward addressing the SFP science question PSF 3, How diverse are planetary systems?
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2. Measuring the masses and spectra of Earth-like planets around a significant number of nearby stars is a challenging technological problem because the contrast
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rePort Panel e l e c t r o M a G n e t I c o b s e r vat I o n s sPace 297 of tHe on froM 6-16 top.eps Redshift bitmap 1 Q 4 2 3 1 Normalized Flux 1 2 3 4 0 Wavelength FIGURE 6.16 Top: Ultraviolet O VI absorption features in circumgalactic gas seen from back illumination from a quasi-stellar object. The gaseous halo is vastly larger than the optical extent of the galaxy and likely contains most of the baryonic matter.
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From page 298... ...
However, cost is likely to be the limiting factor, and so it was good to learn that several engineering groups are experimenting with radical new ways to achieve large-aperture mirrors for space telescopes at a fraction of the weight and cost of the present generation. Deployable segmented mirrors are but one option.
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BLISS represents a consensus approach, as summarized in the U.S. Far-Infrared Astrophysics Community Plan that was submitted to the Astro2010 decadal survey.
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The Necessity of a Healthy Explorer Program The Explorer program has been a key component of the NASA portfolio since the earliest days of the space program. The relatively low-cost astrophysics Explor ers have been highly productive and have provided much of the transformational science of the past 50 years, for example: (1)
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From page 301... ...
The generic utility of the Suborbital program is widely recognized by the community. Of the programs submitted to the EOS Panel by the community, ~25 percent of them incorporated suborbital work (the bulk of which were for the balloon program)
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With suf ficient support, this relatively mature program could be returning science early in this decade. Over the last decade, the balloon program has dominated the science return from the Suborbital program for astrophysics missions.
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A $70 million investment in 2008 supported the processing and archiving of data from NASA missions and provided research grants to guest observers to produce science. Of a further $68 million, half was allocated to development programs, including research-grant support for theory and fundamental physics, data analysis tools, and laboratory astrophysics, and half to technology development and the Suborbital program.
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From page 304... ...
However, by later in the decade -- when an exoplanet mission might be selected -- SIM Lite may not be the best way forward. NASA should continue to respond to new technologies in this area to provide a broad range of options when the time comes.
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Although this level of suppression is deemed a tractable technological problem, significant investments in traditional and nontraditional coronographs, coatings, and deformable mirrors will have to be made. Technology for the Future The directed program outlined above is meant to close technology gaps in order to move ahead with high-priority missions in key science areas.
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. To pick one example, external star shades may allow enhanced planet searches with telescopes that are also well suited for ultraviolet observations, thus serving two high-priority science programs and a wide array of science investigations.
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From page 307... ...
. Because the R&A program supports a wide variety of research, including technology development, the Suborbital program, laboratory astrophysics, and theory, all of this research has been adversely affected by declining funding levels.
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From page 308... ...
Sufficient funds are identified to build WFIRST, to augment the Explorer program for astrophysics by $500 million over the period, to start IXO,12 and to fund a small exoplanet mission or start a larger one. The Explorer program, in fact, is part of the base budget, but the panel includes the augmentation it is recommending in the "new initiatives" category because the amount it recommends is too large to be accommodated by changing priori ties within the base budget.
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From page 309... ...
As described above, this choice would be made later in the decade by selective competition between SIM Lite and one of the alternatives discussed in the section "Missions to Search for and Study Exoplanets." In Table 6.3, the budget below "nominal" -- in yellow -- would provide a bare start for IXO, but no funding for an exoplanet mission. In this scenario, it is crucial to maintain a healthy Explorer program so that some diverse science goals can still be pursued, albeit at a much more modest level.
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