Unveiling non-gray surface of cloudy exoplanets: the influence of wavelength-dependent surface albedo and cloud scattering properties on retrieval solutions

Abstract

Direct-imaging spectra hold rich information about a planet's atmosphere and surface, and several space-based missions aiming at such observations will become a reality in the near future. Previous spectral retrieval works have resulted in key atmospheric constraints under the assumption of a gray surface, but the effect of wavelength-dependent surface albedo on retrieval has not been shown. We explore the influence of the coupling effect of cloud and wavelength-dependent surface albedo on retrieval performance via modeling suites of Earth-like atmospheres with varying cloud and surface albedo parameterizations. Under the assumption of known cloud scattering properties, the surface spectral albedos can be reasonably recovered when the surface cover represents that of Earth-like vegetation or ocean, which may aid in characterizing the planet's habitability. When the cloud scattering properties cannot be assumed, we show that the degeneracy between the cloud properties and wavelength-dependent surface albedo leads to biased results of atmospheric and cloud properties. The multi-epoch visible band observations offer limited improvement in disentangling this degeneracy. However, the constraints on atmospheric properties from the combination of UV band (R $\sim 6$) $+$ visible band (R $\sim 140$) are consistent with input values to within 1 $\sigma$. If short bandpass data is not available, an alternative solution to reduce the retrieval uncertainties would be to have the prior constraints on planetary cloud fraction with less than 20% uncertainty.

References in corpus (21)

• Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
• Combining high-dispersion spectroscopy (HDS) with high contrast imaging (HCI): Probing rocky planets around our nearest neighbors
• Alien Maps of an Ocean-Bearing World
• Inverting Phase Functions to Map Exoplanets
• Exoplanet Reflected Light Spectroscopy with PICASO
• Effects of a fully 3D atmospheric structure on exoplanet transmission spectra: retrieval biases due to day-night temperature gradients
• Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations
• Vegetation signature in the observed globally-integrated spectrum of Earth: Modeling the red edge strength using simultaneous cloud data and application for extrasolar planets
• Direct detection of exoplanets in the 3 -- 10 micron range with E-ELT/METIS
• Detecting Ocean Glint on Exoplanets Using Multiphase Mapping
• Atmospheric Retrieval for Direct Imaging Spectroscopy of Gas Giants In Reflected Light II: Orbital Phase and Planetary Radius
• ExoReL${}^{\Re }$: A Bayesian Inverse Retrieval Framework For Exoplanetary Reflected Light Spectra
• Information in the Reflected Light Spectra of Widely Separated Giant Exoplanets
• Probing the capability of future direct imaging missions to spectrally constrain the frequency of Earth-like planets
• Directly imaged exoplanets in reflected starlight. The importance of knowing the planet radius
• Using polarimetry to retrieve the cloud coverage of Earth-like exoplanets
• ATLAS and SYNTHE under Linux
• Cloud Parameterizations and their Effect on Retrievals of Exoplanet Reflection Spectroscopy
• Multi-orbital-phase and multi-band characterization of exoplanetary atmospheres with reflected light spectra
• Earth as a Proxy Exoplanet: Deconstructing and Reconstructing Spectrophotometric Light Curves
• Geology and Photometric Variation of Solar System Bodies with Minor Atmospheres: Implications for Solid Exoplanets

Cited by in corpus (5)

• In Search of the Edge: A Bayesian Exploration of the Detectability of Red Edges in Exoplanet Reflection Spectra
• YunMa: Enabling Spectral Retrievals of Exoplanetary Clouds
• Influence of Orbit and Mass Constraints on Reflected Light Characterization of Directly Imaged Rocky Exoplanets
• Planet Earth in reflected and polarized light: II. Refining contrast estimates for rocky exoplanets with ELT and HWO
• Retrieving the Red Edge on Earth-like Planets with Heterogeneous Clouds and Surfaces