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Reflection spectroscopy: a pathway to the atmospheric characterization of Earth-like exoplanets

Presentation #609.04 in the session Earths and Super-Earths.

Published onApr 03, 2024
Reflection spectroscopy: a pathway to the atmospheric characterization of Earth-like exoplanets

It will soon be possible to search for biosignatures in the atmospheres of the nearest Earth-sized, habitable zone exoplanets. While transit spectroscopy is an exciting avenue for this work, most of the nearest habitable zone exoplanets are unlikely to transit. Reflection spectroscopy is a powerful new avenue that could reveal a wealth of information on both transiting and non-transiting worlds. By studying the reflected light from these cool worlds, using the powerful technique of high-resolution spectroscopy, we could learn about their clouds and search for O2 biosignatures – a key indicator of habitability – present in this optical wavelength range. High-Resolution Cross-Correlation Spectroscopy is a well-established technique that has been applied to both the transmission and thermal emission spectra of exoplanets. While it can also be applied to the reflection spectrum of an exoplanet it has not yet delivered a robust detection due to the low albedo of previously targeted Hot Jupiters. I will report on our recent observations untangling the mystery of the unusually reflective LTT9779 b using High-Resolution Cross-Correlation Spectroscopy with the world’s largest optical telescope – the Very Large Telescope with ESPRESSO in 4UT mode. This planet’s reflection properties can illuminate its survival in the hot Neptune photo-evaporation desert. I will also show work on simulating future coronagraphic instruments for characterizing Earth-like planets with an emphasis on how coronagraph size will affect our science returns. For HARMONI/ELT, a first-generation ELT instrument, I will demonstrate the feasibility of characterizing the atmosphere of Proxima b, the nearest rocky exoplanet, in reflected light using the molecule mapping technique. I will show that this planet can be detected in reflected light with HARMONI within a reasonable ~20 hours of integration time. For the Habitable Worlds Observatory, I will demonstrate how liquid water could be detected on Earth-like exoplanets via a detection of rainbow scattering features.

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