Neptune Formed Closer to Sun Than Uranus, Study Finds
Chemical modeling reveals how distinct material reservoirs shaped the development of the solar system's two ice giants.
Updated on Oct. 28, 2026 in Space
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Researchers have determined that Neptune formed from material located closer to the sun than the building blocks of Uranus. Published in the journal Astronomy & Astrophysics, this research used chemical modeling to explain why the two ice giants possess distinct atmospheric compositions.
Why it matters
This finding clarifies the chaotic early formation of our solar system by identifying how chemical reservoirs in the protoplanetary disk dictated the development of the outer planets. It provides a new mechanism for how planets acquired their specific elemental signatures.
Researchers compared planetary atmospheric carbon-oxygen ratios against the composition of ancient dust and gas in the solar disk. The model relies on carbon monoxide tracers to map where volatile compounds condensed into solids relative to the sun.
The players
Atacama Large Millimeter/Submillimeter Array
An international radio telescope facility located in the Atacama Desert used to observe cold dust and gas in space.
NASA
The United States agency responsible for the civil space program and upcoming outer planet exploration missions.
The details
By tracing how volatile compounds—substances that evaporate at relatively low temperatures—condensed at different distances from the sun, the team mapped distinct chemical reservoirs. This process suggests Neptune accreted from material located closer to the sun than the region that formed Uranus. The team utilized data from the Atacama Large Millimeter/Submillimeter Array, a massive radio telescope facility in Chile, to analyze the chemical fingerprints within these atmospheres.
Timeline
October 19, 2026: Researchers published findings in Astronomy & Astrophysics.
2024: Researchers determined the actual colors of Uranus and Neptune.
2026: University of Zurich researchers classified these planets as rocky worlds.
Next decade: NASA plans to launch a Uranus Orbiter and Probe mission.
The Tech Race
This study advances the ongoing effort to reconstruct the solar system's birth by contrasting Neptune and Uranus, which share similar sizes but unique chemical profiles. It precedes the next major milestone in this race, the launch of the NASA Uranus Orbiter and Probe mission.
The findings provide a target for future planetary science missions, specifically the planned NASA Uranus Orbiter and Probe mission. Scientists expect this upcoming probe to return direct measurements that could confirm the chemical origin models established by this study.
The takeaway
Understanding how Neptune and Uranus formed sheds light on the distribution of matter in the early solar system. Observers should track the scientific instrument suite selected for the upcoming NASA Uranus Orbiter and Probe mission for potential validation of these chemical models.
Further reading
For more on the latest celestial discoveries, visit the Space section.
Source note: This article includes information reported by Earth and Sky.
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