A mirage of the cosmic shoreline: Venus-like clouds as a statistical false positive for exoplanet atmospheric erosion

Abstract

Near-term studies of Venus-like atmospheres with JWST promise to advance our knowledge of terrestrial planet evolution. However, the remote study of Venus in the Solar System and the ongoing efforts to characterize gaseous exoplanets both suggest that high altitude aerosols could limit observational studies of lower atmospheres, and potentially make it challenging to recognize exoplanets as "Venus-like". To support practical approaches for exo-Venus characterization with JWST, we use Venus-like atmospheric models with self-consistent cloud formation of the seven TRAPPIST-1 exoplanets to investigate the atmospheric depth that can be probed using both transmission and emission spectroscopy. We find that JWST/MIRI LRS secondary eclipse emission spectroscopy in the 6 $\mu$m opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the sub-cloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semi-major axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolation---a convincing false positive for atmospheric escape and an empirical "cosmic shoreline". However, developing observational and theoretical techniques to identify Venus-like exoplanets and discriminate them from stellar windswept worlds will enable advances in the emerging field of terrestrial comparative planetology.

13 pages, 4 figures, accepted for publication in ApJ Letters

References in corpus (20)

• The NumPy array: a structure for efficient numerical computation
• Most 1.6 Earth-Radius Planets are not Rocky
• Extreme Water Loss and Abiotic O${}_2$ Buildup On Planets Throughout the Habitable Zones of M Dwarfs
• The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Predictions of the atmospheric composition of GJ 1132b
• HST hot-Jupiter transmission spectral survey: Haze in the atmosphere of WASP-6b
• Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets
• Temporal evolution of the high-energy irradiation and water content of TRAPPIST-1 exoplanets
• On the Frequency of Potential Venus Analogs from Kepler Data
• Prospects for Characterizing the Atmosphere of Proxima Centauri b
• A Statistical Comparative Planetology Approach to the Hunt for Habitable Exoplanets and Life Beyond the Solar System
• Near-infrared transmission spectrum of the warm-uranus GJ 3470b with the Wide Field Camera-3 on the Hubble Space Telescope
• The Effects of Refraction on Transit Transmission Spectroscopy: Application to Earth-like Exoplanets
• Strict Upper Limits on the Carbon-to-Oxygen Ratios of Eight Hot Jupiters from Self-Consistent Atmospheric Retrieval
• The Stellar Activity of TRAPPIST-1 and Consequences for the Planetary Atmospheres
• The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets
• Observing Isotopologue Bands in Terrestrial Exoplanet Atmospheres with the James Webb Space Telescope---Implications for Identifying Past Atmospheric and Ocean Loss
• Venus: The Making of an Uninhabitable World

Cited by in corpus (17)

• Revealing the Mysteries of Venus: The DAVINCI Mission
• High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations
• Atmospheres of Rocky Exoplanets
• Predictions for Observable Atmospheres of Trappist-1 Planets from a Fully Coupled Atmosphere-Interior Evolution Model
• Was Venus Ever Habitable? Constraints from a Coupled Interior-Atmosphere-Redox Evolution Model
• Super-Earths and Earth-like Exoplanets
• The Fundamental Connections Between the Solar System and Exoplanetary Science
• A Second Earth-Sized Planet in the Habitable Zone of the M Dwarf, TOI-700
• Synergies between Venus & Exoplanetary Observations
• Bioverse: a simulation framework to assess the statistical power of future biosignature surveys
• Large Interferometer For Exoplanets (LIFE): IX. Assessing the Impact of Clouds on Atmospheric Retrievals at Mid-Infrared Wavelengths with a Venus-Twin Exoplanet
• Photochemistry of Venus-Like Planets Orbiting K- and M-Dwarf Stars
• Atmospheric Dynamics of a Near Tidally Locked Earth-Size Planet
• Tracing the Inner Edge of the Habitable Zone with Sulfur Chemistry
• From exo-Earths to exo-Venuses -- Flux and Polarization Signatures of Reflected Light
• TRAPPIST-1h as an Exo-Titan. I. The Role of Assumptions about Atmospheric Parameters in Understanding an Exoplanet Atmosphere
• The climates and thermal emission spectra of prime nearby temperate rocky exoplanet targets