Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth

Domagal-Goldman, Shawn; Segura, Antígona; Claire, Mark; Robinson, Tyler D.; Meadows, Victoria

doi:10.1088/0004-637x/792/2/90

Cited by 204 publications

(268 citation statements)

References 71 publications

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“…Then, the difficulty will be to discard falsepositivedetections of O 2 . For instance, dioxygen may not necessarily be a biosignature (Domagal-Goldman et al 2014;Wordsworth & Pierrehumbert 2014;Harman et al 2015;Schwieterman et al 2016aSchwieterman et al , 2016b. Lifeless, terrestrial planets in the habitable zone of any type of star can develop oxygendominated atmospheres through photolysis of H 2 O (e.g., Wordsworth & Pierrehumbert 2014) or CO 2 (e.g., Harman et al 2015).…”

Section: Discussionmentioning

confidence: 99%

The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

Fauchez

Rossi

Stam

2017

ApJ

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Earth-like, potentially habitable exoplanets are prime targets in the search for extraterrestrial life. Information about their atmospheres and surfaces can be derived by analyzing thelight of the parent star reflected by the planet. We investigate the influence of the surface albedo A s , the optical thickness b cloud ,thealtitude of water clouds, and the mixing ratio of biosignature O 2 on the strength of the O 2 A-band (around 760 nm) in theflux and polarization spectra of starlight reflected by Earth-like exoplanets. Our computations for horizontally homogeneous planets show that small mixing ratios (η<0.4) will yield moderately deep bands in flux and moderate-to-small band strengths in polarization, and that clouds will usually decrease the band depth in flux and the band strength in polarization. However, cloud influence will be strongly dependent onproperties such as optical thickness, top altitude, particle phase, coverage fraction, andhorizontal distribution. Depending on the surface albedoand cloud properties, different O 2 mixing ratios η can give similar absorption-band depths in flux and band strengths in polarization, especially if the clouds have moderate-to-high optical thicknesses. Measuring both the flux and the polarization is essential to reduce the degeneracies, although it will not solve them,especiallynot for horizontally inhomogeneous planets. Observations at a wide range of phase angles and with a high temporal resolution could help to derive cloud properties and, once those are known, the mixing ratio of O 2 or any other absorbing gas.

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Section: Discussionmentioning

confidence: 99%

The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

Fauchez

Rossi

Stam

2017

ApJ

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“…All other stellar types except the Sun use these surface fluxes as the boundary conditions for those gases. For H 2 and CO we used fixed deposition velocities of 2.4 × 10 s −1 , respectively, corresponding to the maximum rate of transfer into an ocean (Domagal-Goldman et al 2014). For the later stellar types, K7V, M1V, M3V and the three observed MUSCLES stars, the CH 4 boundary condition was changed to a fixed mixing ratio (see also Segura et al 2005;Rugheimer et al 2014).…”

Section: Simulation Set-upmentioning

confidence: 99%

Uv Surface Environment of Earth-Like Planets Orbiting FGKM Stars Through Geological Evolution

Rugheimer

Segura

Kaltenegger

et al. 2015

ApJ

128

253

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The UV environment of a host star affects the photochemistry in the atmosphere, and ultimately the surface UV environment for terrestrial planets and therefore the conditions for the origin and evolution of life. We model the surface UV radiation environment for Earth-sized planets orbiting FGKM stars at the 1AU equivalent distance for Earth through its geological evolution. We explore four different types of atmospheres corresponding to an early Earth atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to present day levels at 2.0 Gyr ago, 0.8 Gyr ago and modern Earth (following Kaltenegger et al. 2007). In addition to calculating the UV flux on the surface of the planet, we model the biologically effective irradiance, using DNA damage as a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago) orbiting an F0V star receives 6 times the biologically effective radiation as around the early Sun and 3520 times the modern EarthSun levels. A pre-biotic Earth orbiting GJ 581 (M3.5V) receives 300 times less biologically effective radiation, about 2 times modern Earth-Sun levels. The UV fluxes calculated here provide a grid of model UV environments during the evolution of an Earth-like planet orbiting a range of stars. These models can be used as inputs into photo-biological experiments and for pre-biotic chemistry and early life evolution experiments.

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“…High-energy stellar flux heats upper planetary atmospheres and initiates photochemistry (e.g., Lammer et al 2007;Miguel et al 2015;Rugheimer et al 2015;Arney et al 2017). UVdriven photochemistry can produce and destroy potential biosignatures (O 2 , O 3 , and CH 4 ) and habitability indicators (H 2 O and CO 2 ) in exoplanet atmospheres (Hu et al 2012;Domagal-Goldman et al 2014;Tian et al 2014;Wordsworth & Pierrehumbert 2014;Gao et al 2015;Harman et al 2015;Luger & Barnes 2015). In particular, the ratio of far-to near-UV flux determines which photochemical reactions will dominate and thus the resultant planetary atmosphere.…”

Section: Uv and Ca Iikemission From M Dwarfsmentioning

confidence: 99%

The MUSCLES Treasury Survey. IV. Scaling Relations for Ultraviolet, Ca ii K, and Energetic Particle Fluxes from M Dwarfs

Youngblood

Loyd

Brown

et al. 2017

ApJ

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110

113

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Characterizing the UV spectral energy distribution (SED) of an exoplanet host star is critically important for assessing its planet's potential habitability, particularly for M dwarfs, as they are prime targets for current and nearterm exoplanet characterization efforts and atmospheric models predict that their UV radiation can produce photochemistry on habitable zone planets different from that on Earth. To derive ground-based proxies for UV emission for use when Hubble Space Telescope (HST) observations are unavailable, we have assembled a sample of 15 early to mid-M dwarfs observed by HST and compared their nonsimultaneous UV and optical spectra. We find that the equivalent width of the chromospheric Ca IIKline at 3933 Å, when corrected for spectral type, can be used to estimate the stellar surface flux in ultraviolet emission lines, including H ILyα. In addition, we address another potential driver of habitability: energetic particle fluxes associated with flares. We present a new technique for estimating soft X-ray and >10 MeV proton flux during far-UV emission line flares (Si IV and He II) by assuming solar-like energy partitions. We analyze several flares from the M4 dwarf GJ 876 observed with HST and Chandra as part of the MUSCLES Treasury Survey and find that habitable zone planets orbiting GJ 876 are impacted by large Carrington-like flares with peak soft X-ray fluxes 10 −3 W m −2 and possible proton fluxes ∼10 2 -10 3 pfu, approximately four orders of magnitude more frequently than modern-day Earth.

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Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth

Cited by 204 publications

References 71 publications

The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

Uv Surface Environment of Earth-Like Planets Orbiting FGKM Stars Through Geological Evolution

The MUSCLES Treasury Survey. IV. Scaling Relations for Ultraviolet, Ca ii K, and Energetic Particle Fluxes from M Dwarfs

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Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth

Cited by 204 publications

References 71 publications

The O2 A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

The O2 A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

Uv Surface Environment of Earth-Like Planets Orbiting FGKM Stars Through Geological Evolution

The MUSCLES Treasury Survey. IV. Scaling Relations for Ultraviolet, Ca ii K, and Energetic Particle Fluxes from M Dwarfs

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The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

The O₂ A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets