False-positive biosignatures are abiotic pathways that generate atmospheric gases normally associated with life, producing signals that can be mistaken for biosignatures. Characterizing these pathways is essential for interpreting any jwst or future-telescope atmospheric detection.
Key abiotic O₂/O₃ pathways
- CO₂ photolysis on rocky M-dwarf planets generates detectable abiotic O₂ and O₃ — particularly problematic because M-dwarfs are preferred targets for transmission spectroscopy
- Hydrogen escape leaves behind oxygen in some young atmospheres
Refined 2026 modeling
A photochemical study in a Mars-like atmosphere found that water-vapor-driven HOx chemistry recycles CO and O back to CO₂, suppressing O₂/O₃ buildup. The revised maximum abiotic O₂ is ~2.7% at H = 0.0065 ppm — about 10× lower than earlier estimates (src-oxygen-false-positive-biosignatures-2026-03).
Implication
Detection of O₂ on an M-dwarf rocky planet cannot be interpreted as life without first ruling out CO₂-photolysis + HOx chemistry as the source. This is directly relevant to any future JWST or HWO biosignature claim, including the ongoing debate over K2-18b’s DMS detection. sara-seager et al. (2025) treat false positives as a core reason single-gas detections on their own cannot confirm life — “parallel interpretations” will require next-gen facilities to resolve (src-jwst-biosignature-prospects-2025).
Solar-system extension: panspermia contamination
Per src-venus-panspermia-earth-origin-2026-04, a jhuapl/sandia-national-laboratories team modeled Earth-to-Venus panspermia cell-transfer rates and found that ~100 viable Earth-derived cells per year may reach venus’s clouds (~20 billion over 1 Gyr). This adds a panspermia-contamination failure mode to the false-positive taxonomy: any positive Venus-cloud life detection would carry a non-trivial Earth-origin prior rather than implying independent abiogenesis. The same logic extends to other tightly-coupled planetary systems such as trappist-1.