Table 3
Summary of the parameters used in the retrievals, their expected values, and their prior distributions.
| Parameter | Description | Prior | Expected values (1) | |||
|---|---|---|---|---|---|---|
| Modern | NOE | GOE | Prebiotic | |||
 |
P–T parameter (degree 4) | U(0.5,1.8) | 0.694 | 1.117 | 0.999 | 1.189 |
| a3 | P–T parameter (degree 3) | U(0,100) | 18.644 | 17.562 | 12.886 | 19.430 |
| a2 | P–T parameter (degree 2) | U(0,500) | 110.331 | 72.414 | 59.984 | 71.778 |
| a1 | P–T parameter (degree 1) | U(0,500) | 177.997 | 140.294 | 123.764 | 120.546 |
| a0 | P–T parameter (degree 0) | U(0,1000) | 293.601 | 307.747 | 290.306 | 280.615 |
| log10 (P0 [bar]) | Surface pressure | U(−4,3) | 0.007 | 0.017 | 0.008 | 0.008 |
| Rpl [R⊕] | Planet radius (bulk value) | G(1.0,0.2) | 1.000 | 1.000 | 1.000 | 1.000 |
| log10(Mpl [M⊕]) | Planet mass (bulk value) | G(0.0,0.4) | 0.000 | 0.000 | 0.000 | 0.000 |
| log10(N2) | N2 mass fraction | U(−15,0) | −0.113 | −0.016 | −0.005 | −0.073 |
| log10(O2) | O2 mass fraction | U(−15,0) | −0.631 | −1.623 | −2.622 | −6.002 |
| log10(H2O) | H2O mass fraction | U(−15,0) | −2.607 | −2.143 | −2.498 | −2.345 |
| log10(CO2) | CO2 mass fraction | U(−15,0) | −3.265 | −1.807 | −1.806 | −0.827 |
| log10(CH4) | CH4 mass fraction | U(−15,0) | −6.028 | −3.635 | −3.035 | −6.056 |
| log10(O3) | O3 mass fraction | U(−15,0) | −6.436 | −6.567 | −7.412 | −10.301 |
| log10(CO) | CO mass fraction | U(−15,0) | −7.215 | −6.072 | −7.206 | −4.915 |
| log10(N2O) | N2O mass fraction | U(−15,0) | −6.343 | −6.859 | −7.962 | – |
Notes. U(x, y) denotes a boxcar prior with a lower threshold x and upper threshold y; G(μ, σ) represents a Gaussian prior with mean μ and standard deviation σ. For a4 we chose a prior on 
, which allows us to sample small values more densely, typical of a fourth-order coefficient, and then take the fourth power to obtain a4. The expected values of the P–T parameters are generated by fitting the input P–T profiles (calculated by Rugheimer & Kaltenegger 2018) with a fourth-degree polynomial. The expected values of the abundances are calculated considering the weighted mean by the pressure of the input abundance profiles (calculated by Rugheimer & Kaltenegger 2018).
References. (1) Rugheimer & Kaltenegger (2018).
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