Imaging Habitable Planets
Imaging Habitable Planets |
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Show content only (no menu, header)AbstractDirect imaging of exoplanets is essential to characterize their surfaces and atmospheres, and identify biological activity. Direct observation of exoplanets is however extremely challenging, due to the large ratio between starlight and planet light, combined with the small angular separation between the two objects. Conventional telescopes cannot perform such observations, and newly developped optical techniques, specifically designed for high contrast imaging, must be employed.Habitable Planets: Observational Perspectives and ChallengesAbout one thousand planets have been identified around nearby stars. Essentially all of them have been discovered with indirect detection techniques that monitor the effect the planet(s) have on its host star: radial velocity (induced ), transit ().CoronagraphyConventional telescope, even in the absence of wavefront errors, are not suitable for high contrast imaging, as diffraction from the edge of the pupil creates Airy rings in the focal plane. The rings are much too bright to allow detection of planets, which The role of a coronagraph is to
Wavefront Control: Extreme Adaptive OpticsImaging Habitable Planets from SpaceImaging Habitable Planets with Ground-based TelescopesThe unprecedented angular resolution soon to be offered by extremely large telescopes (ELTs), together with recently developed high contrast imaging techniques (coronagraphy and wavefront control), will enable direct imaging and spectroscopic characterization of potentially habitable planets around nearby M-type stars. While the habitable zones of M stars is challenging to resolve, the planet to star contrast and the apparent brightness of the planet are highly favorable, thus providing the only reliable opportunity for direct imaging and spectroscopic characterization of habitable planets from the ground. The key to imaging and characterizing such planets lies in the ability to perform high contrast imaging (approximately 1e-5 raw contrast) at $\approx$ 1 λ/D with high photometric efficiency. Technical solutions to this challenge now exist, as illustrated by the recent development of a full throughput coronagraph concept offering sub-λ/D inner working angle at high contrast on segmented apertures, and schemes to achieve the necessary level of pointing and low order wavefront error control. Demonstrations of these key techniques are ongoing in laboratories and on ground-based telescopes, already yielding encouraging results. We conclude that a highly specialized, but relatively simple, high contrast imaging system can be build for ELTs within this decade, and that it would likely provide the first opportunity to acquire high quality spectra of habitable planets, before space-based telescope can provide similar capabilities for brighter F-G-K type stars.Page content last updated: 27/06/2023 06:35:52 HST html file generated 27/06/2023 06:34:38 HST |