Decoding Alien Skies:

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1. Scientific Context (Photonics)

Transmission spectroscopy measures wavelength-dependent photon attenuation during planetary transit. Each spectral channel probes a distinct effective optical path length through the atmosphere.

• Photon–molecule interaction
• Absorption cross-sections σ(λ)
• Instrument-limited spectral resolution

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2. Target Properties

• Mass: 0.28 M_J
• Radius: 1.27 R_J
• g ≈ 8.5 m s⁻²
• T_eq ≈ 1100 K

Low gravity results in a large atmospheric scale height, enhancing photonic detectability.

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3. JWST Observations

• NIRISS SOSS: 0.6–2.8 μm
• NIRSpec PRISM: 0.6–5.0 μm

Data correspond to binned transmission spectra from public JWST ERS releases, shown with 1σ uncertainties.

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4. Transmission Spectrum

Distinct absorption bands correspond to molecular opacities and Rayleigh scattering at short wavelengths.

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5. Forward Atmospheric Model

Isothermal hydrostatic atmosphere:

H = k_BT / (μg)

• Molecular opacity: H₂O, CO₂
• Rayleigh scattering ∝ λ⁻⁴
• Grey cloud deck (P_cloud)

This model isolates photonic sensitivity without full retrieval degeneracies.

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6. Residuals & Fit Quality

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7. NIRISS vs NIRSpec Consistency

Independent instruments show consistent photonic signatures, validating instrumental calibration.

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8. Photonic Interpretation

• Absorption depth ∝ effective optical depth
• CO₂ at 4.3 μm detected at high significance
• Photon noise dominates outside molecular bands

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9. Conclusions

• JWST enables molecular-scale photonic sensing
• WASP-39b shows clear H₂O and CO₂ absorption
• Simple forward models reproduce key observables