Methane in the Solar System

Guzmán-Marmolejo, Andrés; Segura, A.

doi:10.18268/bsgm2015v67n3a2

Cited by 20 publications

(11 citation statements)

References 107 publications

(104 reference statements)

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“…>10 14 cm -2 s -1 ). For comparison, biological production of CH4 on Earth corresponds to 1.2x10 11 cm -2 s -1 , of which a significant proportion is due to human activity (Guzmán-Marmolejo and Segura 2015;Houghton 1995;Segura et al 2005).…”

Section: Amount Of Phosphine Required For Detection Via Transmission mentioning

confidence: 99%

“…Values in italic correspond to atmospheric scenarios where PH3 is at a runaway threshold (see Figure 5, and Sections 4.1.3 and 5.1). For comparison, the maximum recorded surface flux of PH3 on Earth is 10 14 cm -2 s -1 (above sewage plants, Devai et al 1988), and the biological production of CH4 on Earth corresponds to 1.2x10 11 cm -2 s -1 (Guzmán-Marmolejo and Segura 2015;Houghton 1995;Segura et al 2005).…”

Section: Atmospheric Scenario Required Mixing Ratio For Detection (Inmentioning

confidence: 99%

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Phosphine as a Biosignature Gas in Exoplanet Atmospheres

et al. 2020

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A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O2, only a handful of gases have been considered in detail. Here we evaluate phosphine (PH3). On Earth, PH3 is associated with anaerobic ecosystems, and as such it is a potential biosignature gas in anoxic exoplanets.We simulate the atmospheres of habitable terrestrial planets with CO2-and H2-dominated atmospheres, and find that phosphine can accumulate to detectable concentrations on planets with surface production fluxes of 10 10 -10 14 cm -2 s -1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition, and UV irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane, or CH4 (10 11 cm -2 s -1 ) and below the maximum local terrestrial PH3 production rate (10 14 cm -2 s -1 ). As with other gases, PH3 can more readily accumulate on low-UV planets, e.g. planets orbiting quiet M-dwarfs or with a photochemically generated UV shield.If detected, phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection. PH3 also has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared to other dominant spectroscopic molecules. PH3's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST time are required for a potential detection of PH3. Yet, because PH3 is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H2O and CH4), searches for PH3 can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability.

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Section: Amount Of Phosphine Required For Detection Via Transmission mentioning

confidence: 99%

Section: Atmospheric Scenario Required Mixing Ratio For Detection (Inmentioning

confidence: 99%

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

et al. 2020

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“…Methane (CH 4 ) is fundamental to our understanding of planet formation and other processes that influence the composition of an exoplanet's atmosphere ( Öberg et al 2011;Barman et al 2011a). Methane is detected on the majority of Solar System planets, represents a large fraction of the carbon budget in gas giant planets, and is a significant greenhouse gas produced by biological and geological processes on Earth (Lunine 1993;Karkoschka 1994;Keppler et al 2006;Guzmn-Marmolejo & Segura 2015). Detecting and constraining methane is extremely important for characterizing exoplanets as a whole.…”

Section: Introductionmentioning

confidence: 99%

Methane in Analogs of Young Directly Imaged Exoplanets

Miles

Skemer

Barman

et al. 2018

ApJ

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We present detections of methane in R of ∼1300, L band spectra of VHS 1256 b and PSO 318.5, two low gravity, red, late L dwarfs that share the same colors as the HR 8799 planets. These spectra reveal shallow methane features, which indicate VHS 1256 b and PSO 318.5 have photospheres that are out of chemical equilibrium. Directly imaged exoplanets usually have redder near infrared colors than the field-age population of brown dwarfs on a color magnitude diagram. These objects along the L to T transition show reduced methane absorption and evidence of photospheric clouds. Compared to the H and K bands, L band (3 µm -4 µm) spectroscopy provides stronger constraints on the methane abundances of brown dwarfs and directly imaged exoplanets that have similar effective temperatures as L to T transition objects. When combined with near infrared spectra, the L band extends our conventional wavelength coverage, increasing our understanding of atmospheric cloud structure. Our model comparisons show relatively strong vertical mixing and photospheric clouds can explain the molecular absorption features and continua of VHS 1256 b and PSO 318.5. We also discuss the implications of this work for future exoplanet focused instruments and observations with the James Webb Space Telescope.

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“…Methane exists in other locations besides Earth throughout the solar system, including in the atmospheres of the outer planets and in comets ( 92 ). While super-Earths and sub-Neptune planets do not exist in our solar system, they are common among other planetary systems, and future studies could determine the surface pressures necessary for these planets to sustain methane via thermochemical recombination, without the need for a significant surface flux ( SI Appendix , section 5 ).…”

Section: Resultsmentioning

confidence: 99%

The case and context for atmospheric methane as an exoplanet biosignature

Thompson

Krissansen‐Totton

Wogan

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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Significance Astronomers will soon begin searching for biosignatures, atmospheric gases or surface features produced by life, on potentially habitable planets. Since methane is the only biosignature that the James Webb Space Telescope could readily detect in terrestrial atmospheres, it is imperative to understand methane biosignatures to contextualize these upcoming observations. We explore the necessary planetary context for methane to be a persuasive biosignature and assess whether, and in what planetary environments, abiotic sources of methane could result in false-positive scenarios. With these results, we provide a tentative framework for assessing methane biosignatures. If life is abundant in the universe, then with the correct planetary context, atmospheric methane may be the first detectable indication of life beyond Earth.

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Methane in the Solar System

Cited by 20 publications

References 107 publications

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

Methane in Analogs of Young Directly Imaged Exoplanets

The case and context for atmospheric methane as an exoplanet biosignature

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