Our solar system just got a little more crowded. Far beyond the orbit of Neptune, astronomers have spotted a new, distant world that might soon join the exclusive club of dwarf planets alongside Pluto. Here’s what we know about 2026 ED138.
A New Face in the Outer Darkness
Scientists using
the Vera C. Rubin Observatory in Chile recently announced the discovery of 2026 ED138, a large object located in the Kuiper Belt, a vast ring of icy bodies circling the edge of our solar system. This frigid, distant region is home to countless comets, icy rocks, and several other known dwarf planets. The discovery was made by astronomer Matthew Holman while refining the observatory's methods for finding distant objects. The object is currently about 46 astronomical units (AU) from the sun, meaning it is 46 times farther from the sun than Earth is. For comparison, Pluto's average distance is about 40 AU. This finding is part of a new wave of discoveries expected from the Rubin Observatory, which has already cataloged thousands of new objects in our cosmic backyard.
The Dwarf Planet Checklist
So, what makes a celestial body a dwarf planet? Back in 2006, the International Astronomical Union (IAU) established a formal definition that famously led to Pluto's reclassification. An object must meet three criteria to be a full-fledged planet: it must orbit the sun, be massive enough for its own gravity to pull it into a nearly round shape, and have 'cleared its orbital neighbourhood' of other objects. A dwarf planet meets the first two criteria—it orbits the sun and is round—but fails the third. Pluto shares its orbital space with many other objects in the Kuiper Belt, which is why it was recategorized. This distinction separates planets from the many other worlds that exist in our solar system.
Making the Case for 2026 ED138
The big question now is whether 2026 ED138 qualifies. Based on its brightness and distance, scientists estimate its diameter to be somewhere between 600 and 1,500 kilometres. An icy body of this size is very likely to have enough mass and gravity to have pulled itself into a spherical shape, a key requirement for a dwarf planet. This would make it one of the largest such objects found beyond Neptune. However, this is still a preliminary analysis. Confirmation requires further observations, likely using infrared telescopes, to determine its exact size and confirm that it is indeed round. Researchers are also examining archival images and have found the object in data going back as far as 2016, which will help them precisely map its 283-year orbit around the sun.
Not Just Pluto Anymore
While Pluto is the most famous dwarf planet, it's not alone. The IAU officially recognizes five dwarf planets to date. Ceres is the only one located in the inner solar system, residing in the main asteroid belt between Mars and Jupiter. The other four—Pluto, Eris, Haumea, and Makemake—are, like 2026 ED138, found in the cold, distant Kuiper Belt. Eris is actually more massive than Pluto, and its discovery was a major catalyst for the 2006 debate on the definition of a planet. Haumea is notable for its strange, football-like shape caused by its incredibly fast rotation. The potential addition of 2026 ED138 to this list highlights that the family of dwarf planets is still growing. Astronomers suspect there could be over a hundred more waiting to be confirmed.
