Towards Polarimetric Exoplanet Imaging with ELTs


A prime science goal of Extremely Large Telescopes (ELTs) is the detection and characterization of exoplanets to answer the question: are we alone? ELTs will obtain the first direct images of rocky exoplanets in the habitable zone and search for atmospheric biomarkers. However, the required instrumental technologies are not yet at a level where an instrument could be built that would achieve this goal. Polarimetry will be an important ingredient in future high-contrast instruments as it will provide a major contrast improvement for planets located within the first two Airy rings and offers unique diagnostic capabilities for liquid water (ocean glint, water clouds and their rainbows), hazes and dust in exoplanetary atmospheres.

We will describe novel instrumental approaches to improving subsystems, in particular polarimetry, wavefront sensing and adaptive optics control. To reach contrasts of 10-9 and beyond to image rocky exoplanets from the ground, a series of individually optimized subsystems cannot succeed; rather, entire combinations of subsystems must be optimized together. We will describe our efforts at measuring and controlling wavefronts with 40'000 degrees of freedom, reaching the photon-noise limit in high-contrast polarimetric imaging at telescopes and our plans to reach a contrast of at least 10-9 in broadband light under realistic, simulated ground-based conditions in the laboratory and to test new approaches at telescopes, in particular achromatic aperture and focal-plane coronagraphs, focal-plane wavefront-sensing and speckle suppression, integral- field polarimetry and high-contrast data reduction algorithms.

Search for Life Beyond the Solar System. Exoplanets, Biosignatures & Instruments