In Search of the Edge: A Bayesian Exploration of the Detectability of Red Edges in Exoplanet Reflection Spectra

• Published in: arXiv.org
• Main Authors: Jonathan Gomez Barrientos, MacDonald, Ryan J, Lewis, Nikole K, Kaltenegger, Lisa
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 04.01.2023
• Subjects: Albedo; Atmospheric composition; Earth analogs; Extrasolar planets; Model accuracy; Parameterization; Physics - Earth and Planetary Astrophysics; Physics - Instrumentation and Methods for Astrophysics; Reflection; Spectra; Spectral signatures; Spectrum analysis; Surface properties; Terrestrial planets
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2301.01775

Reflection spectroscopy holds great promise for characterizing the atmospheres and surfaces of potentially habitable terrestrial exoplanets. The surface of the modern Earth exhibits a sharp albedo change near 750 nm caused by vegetation - the red edge - which would leave a strong spectral signature if present on an exoplanet. However, the retrieval of wavelength-dependent surface properties from reflection spectra has seen relatively little study. Here, we propose a new surface albedo parameterization capable of retrieving the wavelength location of a priori unknown 'edge-like' features. We demonstrate that a wavelength-dependent surface albedo model achieves higher accuracy in retrieving atmospheric composition. Wavelength-dependent surfaces are also generally preferred over a uniform albedo model when retrieving simulated reflection spectra for a modern Earth analog, even for moderate signal-to-noise ratios (S/N = 10) and Earth-like clouds. Further, the location of the modern Earth's red edge can be robustly and precisely constrained (within 70 nm for S/N = 10). Our results suggest that future space-based direct imaging missions have the potential to infer surface compositions for rocky exoplanets, including spectral edges similar to those caused by life on the modern Earth.