Dim Prospects for Transmission Spectra of Ocean Earths Around M Stars

Abstract

The search for water-rich Earth-sized exoplanets around low-mass stars is rapidly gaining attention because they represent the best opportunity to characterize habitable planets in the near future. Understanding the atmospheres of these planets and determining the optimal strategy for characterizing them through transmission spectroscopy with our upcoming instrumentation is essential in order to constrain their environments. For this study, we present simulated transmission spectra of tidally locked Earth-sized ocean-covered planets around late-M to mid-K stellar spectral types, utilizing GCM modeling results previously published by Kopparapu et al. (2017) as inputs for our radiative transfer calculations performed using NASA's Planetary Spectrum Generator (psg.gsfc.nasa.gov; Villanueva et al. (2018)). We identify trends in the depth of H${}_2$O spectral features as a function of planet surface temperature and rotation rate. These trends allow us to calculate the exposure times necessary to detect water vapor in the atmospheres of aquaplanets through transmission spectroscopy with the upcoming James Webb Space Telescope (JWST) as well as several future flagship space telescope concepts under consideration (LUVOIR and OST) for a target list constructed from the TESS Input Catalog (TIC). Our calculations reveal that transmission spectra for water-rich Earth-sized planets around low-mass stars will be dominated by clouds, with spectral features < 20 ppm, and only a small subset of TIC stars would allow for the characterization of an ocean planet in the Habitable Zone. We thus present a careful prioritization of targets that are most amenable to follow-up characterizations with next-generation instrumentation, in order to assist the community in efficiently utilizing precious telescope time.

Accepted to the Astrophysical Journal. 25 pages, 10 figures

References in corpus (13)

• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• Was Venus the First Habitable World of our Solar System?
• Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate
• Tidal Locking of Habitable Exoplanets
• Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars
• Impact of Clouds and Hazes on the Simulated JWST Transmission Spectra of Habitable Zone Planets in the TRAPPIST-1 System
• The atmospheric circulation and climate of terrestrial planets orbiting Sun-like and M-dwarf stars over a broad range of planetary parameters
• TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Motivations and protocol version 1.0
• Clouds will likely prevent the detection of water vapor in JWST transmission spectra of terrestrial exoplanets
• A discontinuity in the $T_{\mathrm{eff}}$-radius relation of M-dwarfs
• Habitability of waterworlds: runaway greenhouses, atmospheric expansion and multiple climate states of pure water atmospheres
• Simulated Phase-dependent Spectra of Terrestrial Aquaplanets in M Dwarf Systems

Cited by in corpus (32)

• Persistence of Flare-Driven Atmospheric Chemistry on Rocky Habitable Zone Worlds
• Aerosols in Exoplanet Atmospheres
• Atmospheres of Rocky Exoplanets
• The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Part III: Simulated Observables -- The return of the spectrum
• Detectability of Molecular Signatures on TRAPPIST-1e through Transmission Spectroscopy Simulated for Future Space-Based Observatories
• Distinguishing between wet and dry atmospheres of TRAPPIST-1 e and f
• Characterizing Atmospheres of Transiting Earth-like Exoplanets Orbiting M Dwarfs with James Webb Space Telescope
• JWST Noise Floor II: Systematic Error Sources in JWST NIRCam Time Series
• The First Habitable Zone Earth-sized Planet from TESS. III: Climate States and Characterization Prospects for TOI-700 d
• Water Ice Cloud Variability & Multi-Epoch Transmission Spectra of TRAPPIST-1e
• Evaluating the Plausible Range of N2O Biosignatures on Exo-Earths: An Integrated Biogeochemical, Photochemical, and Spectral Modeling Approach
• Detecting the proposed CH4-CO2 biosignature pair with the James Webb Space Telescope: TRAPPIST-1e and the effect of cloud/haze
• Bioverse: The Habitable Zone Inner Edge Discontinuity as an Imprint of Runaway Greenhouse Climates on Exoplanet Demographics
• Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-2095
• Bioverse: a simulation framework to assess the statistical power of future biosignature surveys
• Longitudinally asymmetric stratospheric oscillation on a tidally locked exoplanet
• GCM Constraints on the Detectability of the CO${}_2$-CH${}_4$ Biosignature Pair on TRAPPIST-1e with JWST
• Greater climate sensitivity and variability on TRAPPIST-1e than Earth
• H${}_2$-dominated Atmosphere as an Indicator of Second-generation Rocky White Dwarf Exoplanets
• Prospects for water vapor detection in the atmospheres of temperate and arid rocky exoplanets around M-dwarf stars
• MIRECLE: Science Yield for a Mid-IR Explorer-Class Mission to Study Non-Transiting Rocky Planets Orbiting the Nearest M-Stars Using Planetary Infrared Excess
• Finding Signs of Life in Transit: High-resolution Transmission Spectra of Earth-like Planets around FGKM Host Stars
• Traveling planetary-scale waves cause cloud variability on tidally locked aquaplanets
• Polarized Signatures of a Habitable World: Comparing Models of an Exoplanet Earth with Visible and Near-infrared Earthshine Spectra
• Stratospheric Clouds Do Not Impede JWST Transit Spectroscopy for Exoplanets with Earth-Like Atmospheres
• The Phase-curve Signature of Condensible Water-rich Atmospheres on Slowly Rotating Tidally Locked Exoplanets
• Multiple moist climate equilibrium states on arid rocky M-dwarf planets: A last-saturation tracer analysis
• Hurricane genesis is favorable on terrestrial exoplanets orbiting late-type M dwarf stars
• Impact of Planetary Parameters on Water Clouds Microphysics
• Artificial Greenhouse Gases as Exoplanet Technosignatures
• The climates and thermal emission spectra of prime nearby temperate rocky exoplanet targets
• Chemistry, Climate, and Transmission Spectra of TRAPPIST-1 e Explored with a Multimodel Sparse Sampled Ensemble