Exoplanet Finder · Blazing the Trail: Enabling Exoplanet Imaging in the Habitable Zone with the European Extremely Large Telescope

Blazing the Trail: Enabling Exoplanet Imaging in the Habitable Zone with the European Extremely Large Telescope

The search for life on alien worlds is an exciting and active field of research in modern astronomy. One of the ambitious goals of exoplanet science is to directly image exoplanets in the surrounding of the host star and characterise them by atmospheric spectroscopy. Such a study can enhance our understanding of the mechanisms involved in the formation and evolution of planets and enable comparison of exoplanetary chemical compositions with the solar system planets. At present, we have already confirmed ~ 4000 exoplanets mostly through indirect detections where the influence of a planet on its star is observed. These detections have revealed an unexpected diversity of exoplanets which are unlike the solar system planets. Although these discoveries put new constraints on planet formation scenarios, they are strongly biased towards the population of very short-period planets close to their stars (< 1-5 Astronomical Units (AU)) and are only probing the late stages of planet evolution after migrations. To fully understand planet formation and early stage evolution, exoplanets located at more than a few AU from their stars need to be observed. High-contrast imaging (HCI) is the only feasible technique to approach this regime of separations. However, two major challenges still need to be overcome: obtaining the required spatial resolution and overcoming the large star/planet contrast (defined as the flux ratio of planet to star brightness). For example, imaging mature gas planets at small angles around low-mass stars requires contrast limits of 10^-7-10^-9 in near infrared (NIR). Only the era of Extremely Large Telescopes (ELTs) will enable such detections from ground. Since exoplanets are 10^4 to 10^10 times fainter than their star, HCI instruments use devices called coronagraphs to reduce the stellar flux without affecting the planet light. However, their performance is affected by optical aberrations of various natures (Earth’s atmospheric turbulence and optical defects). Most of these errors are mitigated by the Adaptive Optics (AO) or Extreme-AO (ExAO) instruments including wavefront sensing, wavefront control techniques and active speckle suppression routines. In addition, the differential errors creating false positive planet signals can be sensed and corrected directly at the focal plane. Several focal plane wavefront sensing (FPWFS) techniques have been proposed and a high and stable planet contrast has been achieved in a space-like steady environment. However, under the AO/ExAO wavefront residuals, imaging and characterising exoplanets at small angles require achieving detection limit at least 10 to 100 times better than the state-of-the-art. No existing ground-based HCI instruments have successfully disentangled the planet signals from stellar residuals at small angles. Addressing this technical challenge, our project tested and characterised different FPWFS techniques in the laboratory and obtained high-contrast in raw science images. Detecting exoplanets is exciting and understanding the structure and evolution of the circumstellar environment in which these planetary systems flourish provides a broader perspective. To advance the current understanding of how planets emanate from the circumstellar material, the project analysed and modelled the data of one of the known complex debris disk system. This data was obtained with SPHERE, which is a HCI instrument installed at the Very Large Telescope (8-meters) in Chile.

Data: CORDIS, © European Union