Simulating reflected light coronagraphy of Earth-like exoplanets with a large IR/O/UV space telescope: impact and calibration of smooth exozodiacal dust

TL;DR

This study uses high-fidelity simulations to assess how exozodiacal dust affects the detection of Earth-like exoplanets with large space telescopes, providing calibration strategies and impact estimates for different system inclinations and dust levels.

Contribution

It introduces detailed simulation methods to quantify exozodiacal dust contamination and proposes a systematic noise penalty factor for exoplanet observation planning.

Findings

Exozodiacal dust can be subtracted down to photon noise limit up to 1000 zodi in face-on systems.

Inclined systems have a lower exozodi subtraction limit, around 50 zodi at 60° inclination.

System distance significantly impacts the systematic noise from exozodiacal dust.

Abstract

Observing Earth-like exoplanets orbiting within the habitable zone of Sun-like stars and studying their atmospheres in reflected starlight requires contrasts of $\sim1\mathrm{e}{-10}$ in the visible. At such high contrast, starlight reflected by exozodiacal dust is expected to be a significant source of contamination. Here, we present high-fidelity simulations of coronagraphic observations of a synthetic Solar System located at a distance of 10 pc and observed with a 12 m and an 8 m circumscribed aperture diameter space telescope operating at 500 nm wavelength. We explore different techniques to subtract the exozodi and stellar speckles from the simulated images in the face-on, the 30 deg inclined, and the 60 deg inclined case and quantify the remaining systematic noise as a function of the exozodiacal dust level of the system. We find that in the face-on case, the exozodi can be subtracted down to the photon noise limit for exozodi levels up to $\sim1000$ zodi using a simple toy model for the exozodiacal disk, whereas in the 60 deg inclined case this only works up to $\sim50$ zodi. We also investigate the impact of larger wavefront errors and larger system distance, finding that while the former have no significant impact, the latter has a strong (negative) impact. Ultimately, we derive a penalty factor as a function of the exozodi level and system inclination that should be considered in exoplanet yield studies as a realistic estimate for the excess systematic noise from the exozodi.