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Terrestrial Planet Finder Coronagraph Science and Technology Definition

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Terrestrial Planet Finder Coronagraph Science and Technology Definition JPL Document D-34923 Terrestrial Planet Finder Coronagraph Science and Technology Definition Team (STDT) Report Editors: Marie Levine, Stuart Shaklan and James Kasting (Penn State University) June 12, 2006 National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California TPF-C STDT REPORT ii TPF-C STDT REPORT Approvals iii TPF-C STDT REPORT Goals for the Terrestrial Planet Finder Coronagraph Mission The question "are we alone?" has its roots deep in human consciousness, and its answer could revo- lutionize our world view. Starting with Galileo's invention of the telescope 400 years ago, which he used to prove the existence of other worlds, and continuing through a century of astonishing dis- coveries—galaxies, stars, planets, and distant oceans—science has given us a dramatically clearer pic- ture of the universe and our place within it. Today, we finally have tools within reach to seek life be- yond Earth, and to answer this age-old question. The Terrestrial Planet Finder-Coronagraph (TPF-C) mission is a giant step towards that goal. Over the last decade, extrasolar planets have been discovered around nearly 200 nearby stars. Most of these planetary systems are quite different from our own—with Jupiter-sized planets orbiting close to their parent stars—mainly because radial velocity measurements are most sensitive to such planets. New observing techniques, such as coronagraphy and nulling interferometry, are needed to detect smaller, Earth-like planets by their own light and to characterize them as possible harbors for life. Characterization of a terrestrial-sized planet at its most fundamental level means learning about its mass, diameter, temperature, and atmospheric and surface composition. The presence of liquid wa- ter is considered a prerequisite for life, and several gases (O2, O3, CH4, N2O) are considered possible indicators of life. Establishing the presence of any of these compounds in a planet’s atmosphere or on its surface requires spectroscopic measurements of the planet’s emitted and reflected light in both the visible/near-IR and the thermal infrared. The TPF-C mission described in this report is the first of two NASA missions that will obtain these required data. The second is TPF-I/Darwin, a NASA/ESA nulling interferometer that is described elsewhere. In addition to detecting and characterizing Earth-like planets, TPF-C will characterize many Jupiter- like giant planets and circumstellar dust disks. Such planetary system constituents provide clues to the course of planet formation, and may affect the habitability of co-existing terrestrial planets by influencing their bombardment histories. These observations must be carried out in space. Ground-based telescopes cannot do the job, for two reasons. First, ground-based telescopes must observe through the turbulence of the atmosphere. Although some of the resulting blurring can be compensated by adaptive optics, it appears infeasible to see a planet as faint as Earth, even for telescopes as large as 100 m in diameter. Second, Earth’s atmosphere contains significant concentrations of the very biogenic gases that one would wish to measure. Separating out the absorption features of an extrasolar planet’s atmosphere from those of Earth’s atmosphere appears to be an intractable problem, given the small number of photons from the observed planet and the resulting limited spectral resolution. Technology progress necessary for TPF-C has been dramatic in recent years. At least a dozen new types of coronagraphs have been invented that might enable us to see an Earth close to a vastly brighter star. Methods for canceling the halo of starlight scattered within the telescope have also been demonstrated, thereby dramatically relaxing the requirements for optical surface quality. In both areas, laboratory tests are currently getting close to achieving flight-quality performance. The telescope mirror itself needs to be relatively large (8m×3.5m), but it is still within reach of current iv TPF-C STDT REPORT fabrication capabilities. Alternative coronagraph designs described in this report might allow the mission to be accomplished with a smaller mirror. A large visible-wavelength space telescope of the quality needed to detect habitable Earth-sized planets would also have important applications to other areas of astrophysics. In particular, it would profoundly advance the science of extragalactic observations, out to the very edge of the universe. Topics of literally cosmic importance could be addressed, including the expansion rate of the uni- verse, dark energy, dark matter, and the formation of the first stars after the Big Bang. With its planned wide-field camera, TPF-C could conduct many of its deep-space observations in parallel with the search and characterization of Earth-like planets. In addition, the mission would provide dedicated time for separate pointed observations in a program that would be open to the general astronomical community. In summary, TPF-C is one of the most scientifically compelling endeavors that the human race can envision today. The technology needed to accomplish the mission is either available already or well within reach. Pursuing this mission would give NASA a leading role in developing science and tech- nology, and will be inspirational to people everywhere. v TPF-C STDT REPORT A Very Brief History With enlightened foresight, in 1985 NASA organized a Planetary Astronomy Committee, to “pro- vide advice on … initiating the search for and characterization of other planetary systems”. In the same year the Space Science Board of the National Research Council of the National Academy or- ganized the Committee on Planetary and Lunar Exploration to “extend its exploration strategy to planetary systems outside the Solar System”. In 1988 NASA organized a Science Working Group to “formulate a strategy for the discovery and study of other planetary systems”. The first extrasolar planets were discovered only a few years later (1995). Soon thereafter NASA established the first Terrestrial Planet Finder (TPF) Science Working Group, which reported in 1999 that TPF “will revolutionize humanity’s understanding of the origin and evolution of planetary systems”, and produced a schematic design of a thermal-infrared TPF Interferometer (TPF-I) to accomplish that task. In 2000 NASA funded an academic-industry competition to devise additional concepts for finding and characterizing Earth-like planets, resulting in dozens of new ideas, among which the leading one was the TPF Coronagraph (TPF-C). In parallel, in 2000, the second TPF SWG was established to develop an initial Science Requirements Document. In 2005 NASA chartered the Science and Technology Definition Team (STDT) to work with the TPF-C Project scientists and engineers, and deliver a mature Science Requirements Document for TPF-C, a narrative on TPF-C’s potential for general astrophysics observations, a Design Reference Mission, an assessment of design concepts and operational scenarios, recommendations on technol- ogy developments needed, a recommended end-to-end science program, assistance in communicat- ing with the astronomical community, and a report summarizing their work. This is that report. The STDT met in plenary session six times throughout 2005 and early 2006, held scores of tele- phone meetings, and exchanged many hundreds of emails. The STDT built on the foundation of two major studies that had just been completed: the Science Requirements Document of the TPF-C SWG (2004); and the Flight Baseline-1 engineering feasibility study of the TPF-C Project Office at JPL and GSFC (2005). The STDT also incorporated the results of five major competitively-awarded Instrument Concept Studies (2006). In addition, the STDT devoted a very substantial effort to the research and writing of the Science Requirements Document and Design Reference Mission sections of this report. This STDT report contains all of the scientific and engineering material requested in the STDT’s Charter (February 2005), delivered on schedule (June 2006). We plan to publish soon five (5) com- panion Volumes which provide the detailed information behind the STDT Report. The Volumes are: 1) Design Reference Mission Studies, 2) Flight Baseline 1 Design Information and Performance Assessment, 3) Instrument Concept Study Reports, 4) TPF-C Technology Plan and 5) Publications. The STDT wishes it could have delivered even more, however, drastic funding cuts imposed in mid- 2005 and early 2006 precluded the development of two additional parts of the study that had been chartered: a section of advice on the conduct of the end-to-end science program (not provided be- cause the Phase-A start has been delayed indefinitely); and a section on a second iteration of the en- gineering study, Flight Baseline-2 (not provided because the engineering staff was no longer funded). We regret these losses, but we expect that they will be made up in the future. With these caveats, we believe that the present study is more than fully responsive to the STDT’s Charter, and we are pleased to be able to present this study to NASA and the community at large. vi TPF-C STDT REPORT Authors STDT Members J. Roger Angel, University of Arizona Michael E. Brown, California Institute of Technology Robert A. Brown, Space Telescope Science Institute Christopher Burrows, Metajiva Mark Clampin, NASA Goddard Space Flight Center Alan Dressler, Carnegie Observatories Henry C. Ferguson, Space Telescope Science Institute Heidi B. Hammel, Space Science Institute Sara R. Heap, NASA Goddard Space Flight Center Scott D. Horner, Lockheed-Martin Garth D. Illingworth, University of California, Santa Cruz N. Jeremy Kasdin, Princeton University James Kasting, Penn State University (Co-Chair) Mark J. Kuchner, NASA Goddard Space Flight Center Douglas Lin, University of California, Santa Cruz Mark S. Marley, NASA Ames Research Center Victoria Meadows, Spitzer Science Center Martin C. Noecker, Ball Aerospace & Technology Corp. Ben R. Oppenheimer, American Museum of Natural History Sara Seager, Carnegie Institution of Washington Michael Shao, NASA Jet Propulsion Laboratory Karl R.
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