of that space mission should be, or even which planet-detection techniques should be employed.10 It is not even clear whether searches are best carried out at infrared, optical, or even ultraviolet wavelengths. This choice awaits the results of the observational studies just described, alongside a vigorous and adaptive program of theoretical and laboratory astrophysics investigations that will inform scientists about the diversity of exoplanet atmospheres. Although the case is compelling for technology development for a future space mission beginning early, its emphasis may shift as new discoveries from the ground and space materialize. If progress is sufficiently rapid by mid-decade, then a decadal survey implementation advisory committee (as discussed in Chapter 3) could determine whether a more aggressive program of technology development should be undertaken, possibly including steps toward a technology down-select and a focus on key elements. Either way, decisions on significant, mission-specific funding of a major space mission should be deferred until the 2020 decadal survey, by which time the scientific path forward should be well determined.

In summary, exoplanet astronomy is one of the most rapidly developing and unpredictable fields in modern astronomy. Both the statistical investigations of Kepler and WFIRST, and the location of specific, nearby, potentially habitable Earth-like planets under a strong yet flexible program of ground-based research, are recommended. This combined approach will allow new techniques to be devised and surprising discoveries to be made during the coming decade; see Box 7.2.

The Physics of the Universe: Understanding Scientific Principles

Astronomy has made many contributions to our understanding of basic physics and chemistry, ranging from Newton’s laws of gravitation to the discovery of helium, from providing much of the impetus for understanding nuclear physics to discovering new types of molecules unique to interstellar environments. Perhaps the best-developed recent example has come from high-precision tests of the theory


In considering possible exoplanet missions for the next decade, the committee gave serious consideration to SIMLite but decided against recommending it. SIMLite is technically mature and would provide an important new capability (interferometry). Through precision astrometry it could characterize the architectures of 50 or so nearby planetary systems, provide targets for future imaging missions, and carry out other interesting astrophysics measurements. However, the committee considered that its large cost (appraised by the CATE process at $1.9 billion from FY2010 onward) and long time to launch (estimated at 8.5 years from October 2009) make it uncompetitive in the rapidly changing field of exoplanet science. The planetary architecture science can be more efficiently carried out by the committee’s exoplanet strategy involving Kepler, WFIRST, and the ground-based program. The role of target-finding for future direct-detection missions, one not universally accepted as essential, can be done at least partially by pushing ground-based radial velocity capabilities to a challenging but achievable precision below 10 centimeters per second. Finally, the ancillary astrophysics promised by SIMLite was not judged to be competitive.

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