Development and suborbital validation of technologies for direct imaging of nearby exoplanetary systems in reflected visible wavelengths

Abstract

Primarily through indirect observational techniques, the existence of thousands of exoplanetary systems has been confirmed. However, we still do not have an image of an exoplanetary system in reflected visible light. This is important because planetary systems as old as the solar system (∼5 G yr) have cooled to near equilibrium and are thus no longer as bright as the systems being detected by current infrared coronagraphs. Furthermore, the visible bandpass contains valuable information about aerosols, hazes, and clouds that are unavailable to infrared investigations.Our research group has transitioned key technologies that are necessary for direct imaging of exoplanets and their environments from laboratory to near space using suborbital platforms. Two of our sounding rocket experiments, called Planetary Imaging Concept Testbed Using a Rocket Experiment (PICTURE) and Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B), matured a 0.5m diameter Gregorian telescope, a (600nm to 750nm) visible nulling coronagraph (VNC), a 1024 channel deformable mirror (DM) and a fine pointing system.Following up on these rocket experiments, in 2019 we flew a high-altitude balloon called Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C). It carried a telescope employing a 0.6m diameter Off Axis Parabolic (OAP) primary mirror, a vector vortex coronagraph (VVC), a 97-channel low order and a 1024 element high order DM operating in the 540nm to 660nm wavelength range. Like the rocket experiments, the first balloon flight demonstrated a 5 milliarcseconds (mas) fine pointing capability and the space worthiness of the coronagraph.The latest flight of PICTURE-C occurred on September 28 2022. It was designed to obtain the first high contrast (∼10−6) image of a debris disk, a circumstellar ring produced by the sublimation of cometary material and collisions among asteroids, comets and Kuiper-belt analogs, in reflected visible light. The experiment achieved 1 mas root mean square (RMS) fine pointing stability. Even though unanticipated transient vibrations prevented PICTURE-C from attaining its science goals, the conronagraph demonstrated 4×10−6 contrast over 540nm to 660nm (20% bandwidth).