Astronomers Discover Potential Sixth Dwarf Planet Beyond Pluto

Astronomers have discovered a potentially enormous icy world beyond Pluto that could become the sixth officially recognized dwarf planet in the solar system.

The Discovery

The object, temporarily named 2026 ED138, was identified by Matthew Holman, a senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, using observations from the Simonyi Survey Telescope at the NSF-DOE Vera C. Rubin Observatory. Mario Jurić, a University of Washington astronomy professor who leads Rubin's solar system team, helped gather additional evidence to verify the finding.

Holman discovered the object on the evening of October 13 while using specialized software developed with colleague Kevin Napier to search for previously unidentified objects moving through the solar system. Jurić then examined Rubin's stored observations and located 20 additional detections of ED138, including some captured as early as March 2026. The researchers also identified images of the object in historical records from other surveys dating back to 2016.

"If confirmed as a dwarf planet, ED138 would join a very small family of worlds," Holman said.

"Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation," Jurić said. "It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope."

Size and Classification

ED138 currently lies approximately 46 astronomical units from the Sun. Pluto's average orbital distance is about 40 astronomical units. Because ED138 travels beyond Neptune, astronomers classify it as a trans-Neptunian object.

Astronomers estimate ED138's diameter at between 600 and 1,500 kilometers. The range reflects uncertainty in how much sunlight its surface reflects. An icy object within that size range would generally be expected to have enough gravity to become round, but scientists will need more observations to establish its actual dimensions and determine whether it qualifies as a dwarf planet.

The International Astronomical Union currently recognizes five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake.

Why It Remained Undiscovered

ED138 occupies a region of the sky near the plane of the Milky Way, where millions of stars create a crowded background that made the distant object difficult for earlier telescopes to distinguish. Rubin Observatory's ability to repeatedly observe the Southern Hemisphere sky, combined with advanced computer algorithms, made the discovery possible.

The discovery adds to early results from Rubin as it began gathering observations ahead of its Legacy Survey of Space and Time, which officially started in June 2026. In April, Rubin's solar system researchers reported observations of more than 11,000 previously unknown asteroids, including approximately 380 new trans-Neptunian objects.

Why it matters

If confirmed, 2026 ED138 would become the sixth officially recognized dwarf planet, expanding the known population of large icy worlds beyond Neptune and suggesting more such objects may be found as Rubin continues surveying the southern sky over the next decade.

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Sources

• sciencedaily.com: A giant icy world hiding beyond Pluto could be our sixth dwarf planet | ScienceDaily
• smithsonianmag.com: Astronomers Found a Mysterious Object Orbiting Far Beyond Pluto. It Could Be a New Dwarf Planet Hidden in Our Solar System
• news.ssbcrack.com: Astronomers Discover Massive Icy World Beyond Pluto, a Potential Sixth Dwarf Planet - SSBCrack News

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