Multi-Pixel Imaging by a Spaceborne Hypertelescope for Life Detection on Exoplanets

Resolved images of habitable exoplanets, within tens of parsecs, are of interest for searching biosignatures such as the “Indian-summer” signal. Search for Extraterrestrial Intelligence (SETI) applications are also considered. Forming multi-pixel images of such exoplanets is in principle possible with hypertelescopes, resembling a giant telescope but in dilute form with a large flotilla of small mirrors in space. Simulations show that the proposed Exo-Earth Imager flotilla, with its 100 mirrors of 3 m forming a 100 km meta-aperture, can produce a direct image of an exo-Earth at 3 parsecs, containing 30 × 30 resolved elements. This requires accurate control of the meta-mirror’s shape, preferably parabolic for directly co-phasing the beams co-focused toward a focal spaceship. According to the principle of hypertelescope imaging, a pupil densifier element is also needed in the focal optics for concentrating the planet’s light, otherwise spread within a broad diffractive halo. And exoplanet imaging also requires coronagraphic optics for attenuating the contaminating light from the parent star.