Overview
- A peer‑reviewed paper published in September 2026 reports that Neptune’s deep atmosphere appears substantially richer in oxygen than Uranus’s based on ALMA detections of carbon monoxide and disequilibrium chemistry models.
- Researchers used ALMA CO measurements as a tracer because CO can be mixed up from deep layers into the observable troposphere, and they combined those observations with atmospheric chemistry and protoplanetary disk models to infer deep carbon‑to‑oxygen ratios.
- The team interprets the chemical difference as evidence that Neptune’s building blocks likely formed closer to the young Sun and later migrated outward, while Uranus accreted from a more distant, oxygen‑poor reservoir.
- Authors and institutional statements published on Oct. 20, 2026 emphasize that the result depends on assumptions about vertical mixing and disequilibrium chemistry, so it is not definitive without in situ measurements.
- The paper strengthens calls for a targeted orbiter and probe to the ice giants because direct sampling would measure deep abundances, resolve uncertainties in mixing and chemistry, and sharpen how we use Uranus and Neptune as benchmarks for similar exoplanets.