News2026 ED138: New Dwarf Planet Candidate Found Beyond Pluto by Rubin Observatory
A distant object found in Rubin Observatory data could be one of the largest dwarf planets beyond Neptune. Its classification still depends on follow-up measurements.
Representative licensed photograph, not a photograph of this event, the people involved or the object discussed. Photo: Sam Willis / Pexels (Pexels free-use license).
2026 ED138 is a newly reported dwarf planet candidate beyond Pluto, identified in early data from the U.S.-funded Vera C. Rubin Observatory in Chile. The observatory announced the find on October 27, 2026. Scientists estimate the object is about 600 to 1,500 kilometers (370 to 930 miles) across, but its true diameter and official dwarf-planet status remain unconfirmed.
What did the Rubin Observatory discover?
The object, provisionally designated 2026 ED138, is a trans-Neptunian body currently about 46 astronomical units from the Sun. One astronomical unit is approximately the average Earth–Sun distance; Pluto's average orbital distance is about 40 astronomical units. The distance alone does not make ED138 a planet or a dwarf planet. It identifies the region where the object travels.
According to the Rubin Observatory's original announcement, astrophysicist Matthew Holman spotted the candidate while analyzing telescope data on October 13. A subsequent search uncovered 30 Rubin observations from 20 nights between March and July 2026. Researchers also located older images taken as far back as 2016, providing a longer observational record to refine the orbit.
How big is 2026 ED138, and why is its size uncertain?
The published 600–1,500 kilometer diameter estimate is a range, not a direct measurement. Astronomers can infer a body's size from its brightness only after making assumptions about albedo—how much sunlight its surface reflects. A darker object can be physically larger than a brighter object that looks equally luminous through a telescope.
The National Science Foundation calls ED138 a candidate rather than a confirmed dwarf planet. The distinction matters: under the International Astronomical Union's definition, a dwarf planet must have enough gravity to become nearly round, orbit the Sun, and not be a satellite, while not having cleared its orbital neighborhood. The current observations do not settle every physical property needed to make that determination.
If its size and shape are confirmed, ED138 could join the five dwarf planets formally recognized by the IAU: Ceres, Pluto, Haumea, Makemake and Eris. That possibility should not be described as the discovery of a newly confirmed sixth dwarf planet.
Why was such a large object missed until now?
ED138 lies in a crowded patch of sky near the Milky Way, where background stars can make it difficult to separate a slowly moving solar-system object from distant points of light. Rubin's wide-field camera repeatedly photographs large areas of sky; software compares those observations to find faint objects that shift position over time.
The University of Washington's account of the discovery explains that older telescope surveys often avoided this crowded region or observed it less deeply. ED138's orbit is also inclined by nearly 25 degrees to the solar system's main plane, a clue scientists use when studying how Neptune's gravity reshaped the outer solar system.
What happens next for ED138?
Follow-up observations—especially measurements at longer wavelengths—could better establish the object's size, reflectivity and physical nature. The International Astronomical Union's Minor Planet Center has announced its provisional designation, but a provisional designation is not the same thing as formal dwarf-planet recognition.
For U.S. readers wondering whether the discovery changes the number of planets: no. The solar system still has eight recognized planets, and ED138 has not been declared a ninth planet. It is a potentially important addition to the inventory of distant icy worlds, not a change to Earth's night sky that can be spotted with the naked eye.
For another astronomy topic with practical U.S. observing details, see our earlier October 2026 Hunter's Moon guide; unlike the Moon, ED138 requires advanced astronomical instruments to study.
Primary sources and independent context
- NSF–DOE Vera C. Rubin Observatory: October 27 discovery announcement
- U.S. National Science Foundation: candidate status and estimated size
- University of Washington: research team and discovery method
- Space.com: independent reporting on the candidate
Editorial note: This report reflects verified information available on October 30, 2026. For corrections, use our contact page.