Images of Uranus and Neptune, with their blue hues and similar sizes, make them appear like twins born from the same material in the early solar system. But a new study suggests that this apparent similarity may mask two very different stories. Neptune's unseen interior may contain far more oxygen than Uranus, a difference that could indicate their constituent materials came from different regions around the young Sun.
Hot Topics
The Southwest Research Institute in the United States announced the findings on October 19, 2026, based on a study published in the journal Astronomy & Astrophysics. The researchers relied on recent measurements of gases and models simulating what occurs beneath dense cloud layers.
The telescope cannot directly see the deep layers, so scientists looked for a chemical signature that travels from the bottom to the top: carbon monoxide gas. Its quantity in the observed layers is affected by the abundance of water and oxygen at depth, and by the rate of gas mixing between the layers.
The team combined measurements, including observations from the ALMA telescope network in Chile, with models of atmospheric motion and chemical reactions. They concluded that the oxygen-to-hydrogen ratio on Uranus could be between 62 and 177 times that of the nebula from which the Sun originated, compared to 222 to 342 times that of Neptune, according to one atmospheric mixing model.
The calculations also suggest a difference in the carbon-to-oxygen ratio, although the ranges of uncertainty overlap. Olivier Moses, program director in the Solar System Science and Exploration Division at the Southwest Research Institute, said the two planets appear to be twins, but their chemistry makes them more like two relatives with different histories.
The story dates back to about 4.5 billion years ago, when the young sun was surrounded by a vortex of gas and dust. Temperatures decreased with distance from it, causing different materials to freeze at different distances and become part of the building blocks of planets.
When the researchers compared the two chemical signatures to a model of that ancient disk, they found that Neptune's materials may have formed in a region closer to the sun and then moved outward, while Uranus's materials could have originated further away, near its current location.
Tags:
science