Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets

By Giada N. Arney, V. Meadows, S. Domagal‐Goldman, D. Deming, T. Robinson, G. Tovar, E. Wolf, E. Schwieterman. 2016

134 citations recorded by the source corpus.

Hazes are common in known planetary atmospheres, and geochemical evidence suggests that early Earth occasionally supported an organic haze with significant environmental and spectral consequences. The UV spectrum of the parent star drives organic haze formation through methane photochemistry. We use a 1D photochemical-climate model to examine production of fractal organic haze on Archean Earth-analogs in the habitable zones of several stellar types: the modern and early Sun, AD Leo (M3.5V), GJ 876 (M4V), ϵ Eridani (K2V), and σ Boötis (F2V). For Archean-like atmospheres, planets orbiting stars with the highest UV fluxes do not form haze because of the formation of photochemical oxygen radicals that destroy haze precursors. Organic hazes impact planetary habitability via UV shielding and surface cooling, but this cooling is minimized around M dwarfs, whose energy is emitted at wavelengths where organic hazes are relatively transparent. We generate spectra to test the detectability of haze. For 10 transits of a planet orbiting GJ 876 observed by the James Webb Space Telescope, haze makes gaseous absorption features at wavelengths < 2.5 μm 2–10σ shallower than a haze-free planet, and methane and carbon dioxide are detectable at >5σ. A haze absorption feature can be detected at 5σ near 6.3 μm, but a higher signal-to-noise ratio is needed to distinguish haze from adjacent absorbers. For direct imaging of a planet at 10 pc using a coronagraphic 10 m class ultraviolet–visible–near-infrared telescope, a UV–blue haze absorption feature would be strongly detectable at >12σ in 200 hr.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ed3fec8a2f8c89913c7f06817829534d059c6f84

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Citations in the corpus

Planetary Spectrum Generator: An accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets (2018, methodology): “f) Simulated coronagraphy spectra of an Earth-like planet as observed with LUVOIR (compare to [97]).”
Modeling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets (2017, background): “In particular, if the atmospheric CO2/CH4 ratio is high, and if the emission of TRAPPIST-1 is high in the spectral region ∼ [120-180] nm, where the UV cross section of CO2 / O2 is maximum (Arney et al. (2017), Figure 2c), then the formation of photochemical hazes could be severely halted.”
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life (2017, background): “…to planets orbiting other stars: for example, biosignature gas concentrations and detectability under the UV environments of planets orbiting M stars (Segura et al., 2005; Rugheimer et al., 2015a, 2015b); and organic hazes on Earth-like planets around different stellar types (Arney et al., 2017).”
The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST (2019, background): “…the range of possible atmospheric conditions for the TRAPPIST-1 planets, particularly photochemically and climatically self-consistent reducing atmospheres (e.g., Arney et al. 2017), and UV characterizations of late M dwarfs to improve photochemical predictions and interpretation of observations.”