# Exoplanets & Biosignatures: State of the Field (October 2026)

Research dossier · v1 · updated 2026-10-30 · 4,114 words · 54 sources · 29 claims · verification: verified

This dossier maps exoplanet biosignature science as of October 2026: JWST atmosphere results for giant and rocky planets, the disputed dimethyl sulfide claim for the sub-Neptune K2-18 b, and the stellar-contamination and model-degeneracy problems that limit rocky-planet tests. The main takeaway is that no biosignature gas has been confirmed and the leading claims remain contested.

## Contents

- Executive summary
- Background and core concepts
- Timeline of key milestones
- State of the art
  - Giant and warm planets: photochemistry, clouds and haze
  - Temperate sub-Neptunes: the K2-18 b test case
  - Rocky planets around M dwarfs
  - Stellar contamination and retrieval methods
  - Biosignature theory and false positives
  - Quantitative benchmarks
- Open problems and active debates
- Major programs and players
- Outlook: what to watch (next 12-18 months)
- Key papers
- Glossary

## Sample findings

- JWST transmission spectra of WASP-39b show an absorption feature at 4.05 μm attributed to photochemically produced SO2.
- Thermochemical equilibrium predicts SO2 below 1 ppb in WASP-39b, while photochemistry of H2O and H2S yields 1–10 ppm.

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