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J. I. Lunine (Lunar and Planetary Lab, The University of Arizona)
The holy grail of the search for extra-solar planets is the detection and characterization of Earth-sized planets, the latter in regard to whether they might harbor life. And yet, present technology dictates that extra-solar planet discoveries today are confined to indirect detection, establishment of minimum masses, and (in only one case to date) size via transit observations. There is thus a relatively long road from the current era--which itself is enormously exciting--to that of TPF. Microlensing and transit studies might detect planets nearly the mass or size (respectively) of the Earth long before TPF is launched. However, equally important will be the detection and characterization of extra-solar giant planets. Models of the evolution of giant planets as a function of mass, metallicity and gravity provide specific predictions for the size, brightness and spectral characteristics of such objects with time. These predictions, which seem to accord well with theory where they can be tested (Jupiter, Saturn, HD209458b), provide fertile ground for the testing of techniques for the detection of even fainter and (in terms of their varied evolutionary paths) more poorly understood terrestrial planets. Once the threshold of detection of terrestrial planets is reached, assessment of habitability will require observations in the infrared, and optimally in both infrared and optical, to detect a variety of atmospheric gases that may be present. Because the significance of such gases for life is a function of time during the evolution of a terrestrial planet, few if any signatures by themselves are uniquely diagnostic--the assessment of habitability will also require the parent star's age (hence that of the planet), and other system characteristics.
Some of the work reported here has been supported by the NASA Origins Program.
The author(s) of this abstract have provided an email address for comments about the abstract: jlunine@lpl.arizona.edu