Uranus and Neptune may have different formation histories

New research published in Astronomy & Astrophysics suggests that Uranus and Neptune may have distinct formation or migration histories despite their similar sizes and structures. By using carbon monoxide as an indirect tracer to investigate deep atmospheric chemistry, an international research team led by Tom Briand found that Neptune appears to have a more oxygen-enriched deep atmosphere than Uranus.

Using a chemical-and-diffusion model, researchers inferred carbon-to-oxygen ratios to compare the planets' compositions. The findings suggest that the two planets may have originated from different environments within the protoplanetary disk. One proposed scenario indicates that Neptune may have formed closer to the Sun before migrating outward, while Uranus formed further away.

However, the study notes that a definitive reconstruction of each planet's birthplace is not yet possible. Significant uncertainties remain, particularly regarding vertical atmospheric mixing and the accuracy of chemical-reaction models, which can substantially alter the inferred oxygen ranges.