Rubin Observatory Finds 2026 ED138, a Distant Possible Dwarf Planet

The NSF–DOE Vera C. Rubin Observatory in Chile has found its first dwarf planet candidate: a large, bright world beyond Pluto, given the provisional designation 2026 ED138, which scientists say could be among the largest objects ever discovered in the outer Solar System. The discovery was announced on 27 October by the International Astronomical Union’s Minor Planet Center and presented the same day at the American Astronomical Society’s Division for Planetary Sciences meeting in Spokane, Washington.

It is an early and striking result for an observatory that only began its ten-year Legacy Survey of Space and Time (LSST) this year, and a sign of how many distant objects may still be hiding in the Sun’s outer neighbourhood.

What Is 2026 ED138?

2026 ED138 is a trans-Neptunian object, meaning it orbits the Sun beyond Neptune. According to NOIRLab, which operates Rubin with SLAC, it currently lies about 46 astronomical units (au) from the Sun, where one au is the average Earth–Sun distance. Pluto, for comparison, averages about 40 au.

Its orbit is tilted by roughly 24 to 25 degrees to the plane of the planets, which places it in a population astronomers call “hot classical” Kuiper Belt objects. A technical note shared by the Rubin team on the Rubin Community forum adds that the orbit may lie near a 12:7 resonance with Neptune, although that needs confirming.

How Big Is It, and Is It Really a Dwarf Planet?

That is the open question. Based on its brightness, the team estimates a diameter of somewhere between about 600 and 1,500 kilometres. The wide range exists because astronomers do not yet know how reflective its surface is: a dark object must be larger to appear this bright, while an icy, reflective one could be smaller.

To be classed as a dwarf planet, an object must be massive enough for its own gravity to pull it into a roughly round shape. Infrared observations, which measure heat rather than reflected light, are needed to pin down its size and reflectivity. Only five bodies are currently recognised by the IAU as dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake. For more space and science stories, see our Science section.

How Was It Found?

The object was spotted on 13 October 2026 by Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian, a member of Rubin’s operations team, using software he developed with Kevin Napier to search for slow-moving distant bodies. Rubin had imaged it 30 times over 20 nights between 4 March and 11 July 2026, during the run-up to the main survey.

Researchers then traced it back in older images, including data from the Dark Energy Camera (DECam) in Chile going back to 2016, which helped to establish its orbit. NOIRLab says the object had probably been missed because it sits close to the crowded plane of the Milky Way, where faint moving dots are easily lost among background stars.

“Rubin Observatory’s super power is the ability to clearly capture movement and change among a vast number of objects and phenomena that humans have never seen before,” said Edward Ajhar, NSF Program Director for Rubin Observatory, in the NOIRLab release.

Why Does This Discovery Matter?

Large objects in the outer Solar System are rare, and each one tells scientists something about how the planets formed and migrated billions of years ago. Mario Jurić of the University of Washington, Rubin’s Solar System lead scientist, helped Holman double-check the find, and the pair located the extra Rubin and archival sightings that allowed its orbit to be mapped, according to Scientific American.

The pace is already rapid. In April the Rubin team submitted roughly 11,000 newly discovered asteroids to the Minor Planet Center, including about 380 trans-Neptunian objects. Because Rubin photographs the whole southern sky every few nights, astronomers expect it to find many more faint, distant bodies than earlier surveys.

What Happens Next?

• Follow-up observations: Astronomers will seek infrared and other measurements to estimate size and reflectivity.
• A possible name: If its orbit is secured and it receives a permanent number, the discoverers can propose a name to the IAU.
• More discoveries: Rubin’s survey runs for ten years, so further dwarf planet candidates are widely expected.

Rubin’s discovery comes as space science enjoys a busy autumn, with NASA also setting out its plans for a 2028 crewed Moon landing. Earlier this month the European Space Agency’s Euclid mission spotted a new comet.

Featured image: Rubin Observatory at night by Rubin Observatory/NSF/AURA/A. Pizarro D. via Wikimedia Commons, CC BY 4.0. File photo of the observatory on Cerro Pachón, Chile.

Sources

• NOIRLab — NSF–DOE Vera C. Rubin Observatory Reveals Its First Dwarf Planet Candidate in Our Solar System (27 October 2026).
• Rubin Observatory — Rubin’s first dwarf planet candidate (27 October 2026).
• U.S. National Science Foundation — New dwarf planet candidate discovered by NSF–DOE Rubin Observatory (27 October 2026).
• Scientific American — The Vera C. Rubin Observatory may have just discovered our solar system’s sixth dwarf planet (27 October 2026).
• GeekWire — A new pal for Pluto? Rubin Observatory finds its first dwarf planet candidate (27 October 2026).
• Rubin Community Forum — 2026 ED138: a dwarf-planet candidate found in early Rubin data (27 October 2026).