Large Interferometer For Exoplanets (LIFE): IX. Assessing the Impact of Clouds on Atmospheric Retrievals at Mid-Infrared Wavelengths with a Venus-Twin Exoplanet

Abstract

The Large Interferometer For Exoplanets (LIFE) initiative aims to develop a space based mid-infrared (MIR) nulling interferometer to measure the thermal emission spectra of temperate terrestrial exoplanets. We investigate how well LIFE could characterize a cloudy Venus-twin exoplanet to: (1) test our retrieval routine on a realistic non-Earth-like MIR spectrum of a known planet, (2) investigate how clouds impact retrievals, (3) refine the LIFE requirements derived in previous Earth-centered studies. We run retrievals for simulated LIFE observations of a Venus-twin exoplanet orbiting a Sun-like star located 10 pc from the observer. By assuming different models (cloudy and cloud-free) we analyze the performance as a function of the quality of the LIFE observation. This allows us to determine how well atmosphere and clouds are characterizable depending on the quality of the spectrum. Our study shows that the current minimal resolution ($R=50$) and signal-to-noise ($S/N=10$ at $11.2\mu$m) requirements for LIFE suffice to characterize the structure and composition of a Venus-like atmosphere above the cloud deck if an adequate model is chosen. However, we cannot infer cloud properties. The accuracy of the retrieved planet radius ($R_{pl}$), equilibrium temperature ($T_{eq}$), and Bond albedo ($A_B$) depend on the choice of model. Generally, a cloud-free model performs best and thus the presence of clouds cannot be inferred. This model dependence of retrieval results emphasizes the importance of developing a community-wide best-practice for atmospheric retrieval studies. If we consider higher quality spectra (especially $S/N=20$), we can infer the presence of clouds and pose first constraints on their structure.

Accepted for publication in A&A; Updates: LIFE-series number changed from 10 to 9, additional references added to the discussion, language editing; 15 pages (main text incl. 8 figures and 6 tables) + appendix; comments are welcome. This paper is part of a series on the LIFE telescope. Related series papers: arXiv:2101.07500, arXiv:2203.00471, arXiv:2112.02054, arXiv:2204.10041

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Cited by in corpus (9)

• Large Interferometer For Exoplanets (LIFE): XIII. The Value of Combining Thermal Emission and Reflected Light for the Characterization of Earth Twins
• Earth as an Exoplanet. III. Using Empirical Thermal Emission Spectra as an Input for Atmospheric Retrieval of an Earth-twin Exoplanet
• Parameterizing pressure-temperature profiles of exoplanet atmospheres with neural networks
• Pursuing Truth: Improving Retrievals on Mid-Infrared Exo-Earth Spectra with Physically Motivated Water Abundance Profiles and Cloud Models
• Tracing the Inner Edge of the Habitable Zone with Sulfur Chemistry
• Large Interferometer For Exoplanets (LIFE). XIV. Finding terrestrial protoplanets in the galactic neighborhood
• Artificial Greenhouse Gases as Exoplanet Technosignatures
• Consequences of Non-Gaussian Instrumental Noise in Perturbed Nulling Interferometers
• Is Ozone a Reliable Proxy for Molecular Oxygen? II. The impact of N${}_2$O on the O${}_2$-O${}_3$ relationship for Earth-like atmospheres