Requirements of a nulling space interferometer for the search for extrasolar planets

The direct detection of a planet close to its parent star is challenging because the signal detected from the parent star is between 10(9) and 10(6) times brighter than the signal of a planet in the visual and IR, respectively. Future space based missions like DARWIN and TPF concentrate on the wavelength range between 6 and 18 mum, a region that contain the CO2, H2O, O-3 spectral features of the atmosphere. The presence or absence of these spectral features would indicate similarities or differences with the atmosphere of terrestrial planets. The concepts for space nulling interferometers and the influence of different schemes of beam combination on the detected signal are investigated. Based on the background contribution to the detected signal, the wavelength range where the detection sensitivity should be maximised is identified. The use of integrated optics to combine the spectral channels is discussed. The resulting transmission maps are evaluated on base of the symmetry, rejection values, null depth and applications for extra-solar planet search. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.