A Mission Concept for the Terrestrial Planet finder (TPF)

Sally Heap
NASA's Goddard Space Flight Center


According to the 2000 astrophysics survey, “The main goal of TPF is nothing less than to search for evidence of life on terrestrial planets around nearby stars.” In response, we are working to develop a conceptual design for TPF that can find planets orbiting nearby stars having measurable atmospheric H2O at 0.94 μ, O2 at 0.76 μ and/or O3 at 0.30 μ. The mission is very challenging because Earth-like exoplanets are very faint (V~29) and very close to a much brighter star. Our strawman design uses an on-axis, diffraction-limited 4-m optical telescope and a large deployable occulting mask many 1000’s of km away to shade the telescope from starlight. It also uses photon-counting CCD’s, which cut the exposure time needed to get a spectrum of a planet to 1/5th that for CCD’s with 3-electron read noise.

NASA advisory panels have insisted that TPF carry general-astrophysics instrumentation and that at least half the mission time be devoted to general-astrophysics observations. Their insistence is most welcome, as it would more than double the scientific efficiency of the mission (the time spent while the occulter is maneuvering to the next star could be used for general astrophysics). Our baseline three-mirror anastigmat telescope design could accommodate wide-field imagery or spectroscopy to carry out numerous studies such as weak-lensing studies of dark energy and dark matter, baryonic oscillations, galaxy formation and evolution, and microlensing searches for planets. Our baseline detector for general astrophysics is a mosaic of Teledyne HgCdTe detectors sensitive over the 0.4-1.7-μ spectral range, similar to the IR detector on Wide Field Camera 3 to be installed next year on Hubble.