Astronomers Discover a Giant New Dwarf Planet Candidate Hiding Beyond Pluto

Astronomers have identified 2026 ED138, a large icy object in the Kuiper Belt and the Vera C. Rubin Observatory’s first dwarf-planet candidate. Its estimated diameter ranges from 600 to 1,500 kilometers, potentially putting it among the largest known objects beyond Neptune. The uncertainty comes from its unknown surface reflectivity: a small, bright object can look as luminous as a much larger, darker one. If its size is confirmed, ED138 may be large enough for its gravity to make it roughly spherical, a key characteristic of dwarf planets.

The object was found in Rubin observations from March to July 2026, then traced in archived images dating back to 2016. Those records helped establish its orbit: it takes about 281 years to circle the Sun, traveling between 36.86 and 49.04 astronomical units - within Pluto’s range of distances. Its orbit is tilted about 24.5 degrees, and its position against the crowded Milky Way helped it escape detection. Infrared observations could refine its size and status. The discovery also demonstrates Rubin’s potential to reveal a much fuller picture of the outer Solar System. Its planned decade of repeated sky surveys may uncover thousands of objects, improving understanding of the region’s history and potentially helping test whether the proposed Planet Nine exists.