An international team of astronomers has discovered that Uranus appears to be locked into a long-term orbital relationship with a small icy body, raising new questions about the dynamics of the outer Solar System.
In a new, not-yet-peer-reviewed study highlighted by Universe Today, researchers describe the motion of a minor planet known as 2015 OU₁₉₄ — a “Centaur” object located between Uranus and Neptune.
In early February, the space observatory’s Near-Infrared Camera (NIRCam) caught the minuscule and still-unnamed object orbiting the gas giant at a distance of 35,000 miles.
“It’s a small moon but a significant discovery, which is something that even NASA’s Voyager 2 spacecraft didn’t see during its flyby nearly 40 years ago,” said Southwest Research Institute lead scientist Maryame El Moutamid in a NASA statement.
Unlike most Centaurs, which follow unstable and unpredictable paths, 2015 OU₁₉₄ maintains a remarkably steady orbit, completing three revolutions around the Sun for every four Uranus makes. This resonance prevents the two bodies from either colliding or drifting apart.
Led by Daniel Bamberger of Germany’s Northolt Branch Observatories, the team examined archival data from Japan’s Subaru Telescope in Hawaii and later observations from 2017 and 2018.
Their analysis, supported by simulations, suggests that Uranus and 2015 OU₁₉₄ have shared this orbital rhythm for at least 1,000 years — and possibly for more than a million. Models further predict that the arrangement could remain stable for another 500,000 years.
If confirmed, this would mark the first known example of such a resonance with an outer planet. Additional candidates are already being investigated, including two other Centaurs — 2013 RG₉₈ and 2014 NX₆₅ — that may have comparable relationships with Uranus and Neptune.
The findings offer fresh insight into how minor bodies interact with the gas and ice giants, and could reshape understanding of orbital mechanics in the far reaches of the Solar System.
Uranus is home to 29 known moons, ranging from the massive Titania—981 miles across and the eighth-largest moon in the solar system—to the much smaller Miranda at 290 miles in diameter.
Many of these moons were only discovered when Voyager 2 flew past the planet, adding nearly a dozen to the tally.
At the time of Voyager 2’s visit, Uranus had 15 known moons. Additional observations since then, including help from NASA’s Hubble Space Telescope, have revealed more than a dozen new ones, which tend to be significantly smaller.
