Finding Extrasolar Earthlike Planets: A Visible Light Coronagraphic Approach to NASA's Terrestrial Planet Finder (TPF)

Prof. N. Jeremy Kasdin, Mechanical and Aerospace Engineering, Princeton University

NASA's current strategic plan calls for the launching of a space observatory, The Terrestrial Planet Finder (TPF), by the middle of the next decade; it will search for terrestrial planets in the habitable zone of roughly 150 nearby stars and characterize them for the potential to harbor life. From April 2000 to December 2002, four industry led teams studied potential concepts, under the direction of JPL, for the mission. This talk describes work at Princeton University toward a visible light concept for TPF. Princeton was part of a team led by Ball Aerospace and Technology that including scientists and engineers from throughout the country, including the Harvard/Smithsonian Center for Astrophysics and the Space Telescope Science Institute. The Ball team's concept consists of a 4 meter by 10 meter coronagraphic telescope in a deep space orbit.

The problem to overcome when imaging planets is the high contrast between the light from the parent star and from the planet, coupled with their small angular separation. For a coronagraph, the diffraction pattern of the telescope must be suppressed at the planet location. One approach to achieving the high contrast needed is by using optimized pupil shapes that provide the needed 10 billion times suppression as close as 4 lambda/D to the center of the star. In addition, wavefront errors induced by the mirror deformities must be corrected using deformable mirrors in a novel active optics system that corrects both amplitude and phase errors.

This talk will describe the recent history of planet finding methods that lead up to TPF. It will then discuss the scientific arguments for the mission, the relative merits of a visible light coronagraph over the earlier multi-satellite infra-red interferometer concept, and the baseline design of the telescope and instrument that will meet the mission requirements. A variety of technologies and concepts being worked on at Princeton for TPF will be described, including novel orbit design, diffraction and pupil shape optimization, new materials for phase actuation, and adaptive optics for wavefront control. The talk will conclude with an outline of the current status of TPF and NASA's plans for the future.