Astronomers have found a possible new dwarf planet far beyond Pluto, potentially one of the largest icy worlds ever found in the outer solar system. The object, provisionally named 2026 ED138, was spotted in data from the NSF–DOE Vera C. Rubin Observatory in Chile and announced by the International Astronomical Union Minor Planet Center on October 27, 2026. If confirmed, the new dwarf planet candidate 2026 ED138 would join just five officially recognised dwarf planets and mark the largest trans-Neptunian object found in about two decades.

The discovery is the first dwarf planet candidate from Rubin Observatory, whose giant survey telescope only began its decade-long Legacy Survey of Space and Time in June 2026. It was found in early commissioning data by a scientist running custom search code through billions of detections of moving objects.

Key Points

• 2026 ED138 is a large, bright icy object orbiting about 46 times farther from the Sun than Earth, beyond Pluto's average distance of 40 astronomical units.
• Scientists estimate it is between 600 and 1,500 kilometres across, making it potentially among the largest dwarf planets ever found beyond Neptune.
• It was discovered by Matthew Holman of the Center for Astrophysics at Harvard & Smithsonian in Rubin Observatory data spanning March 4 to July 11, 2026.
• The object hid for years in a crowded patch of sky near the plane of the Milky Way, and was later traced in archive images going back to 2016 and possibly 1954.
• Infrared observations, possibly with the James Webb Space Telescope, are still needed to pin down its exact size and confirm it as a dwarf planet.

What Happened

On the evening of October 13, 2026, Matthew Holman was running data collected by Rubin Observatory earlier in the year through search code he developed with colleague Kevin Napier. The code sifts through billions of detections of moving objects and finds the detections that belong to the same body. That night it flagged something so bright and so distant that it was plainly unusually large.

Holman, a Rubin operations team member at the Center for Astrophysics, checked and rechecked the result; so rare was the finding that his first instinct was that it must be a code bug. It was not. Mario Jurić, a University of Washington astronomy professor and Rubin's solar system lead scientist, searched the observatory's catalogues and found 20 more observations of the same object, from July 11 back to March 4, 2026: 30 observations on 20 nights in total.

The team then traced the object further back in archival images from other surveys to 2016, giving astronomers more than a decade of orbital arc. The International Astronomical Union Minor Planet Center reviewed the work and announced the discovery, publishing data about an orbit tilted 25 degrees from the planets' plane. Holman and Jurić presented the results at the American Astronomical Society's Division for Planetary Sciences meeting in Spokane, Washington.

Background: The Dwarf Planet Family So Far

The International Astronomical Union defines a dwarf planet as an object in orbit around the Sun that is large enough to pull itself into a nearly round shape but has not cleared its orbit of debris. Only five worlds currently hold the title: Pluto, Eris, Haumea and Makemake, all beyond Neptune, and Ceres in the asteroid belt between Mars and Jupiter.

Pluto, the best known of the group, was demoted from full planet status in 2006, a decision that still stirs public debate two decades on. Eris, slightly more massive than Pluto, helped trigger that reclassification. Beyond them sits a long list of suspected dwarf planets awaiting the measurements that would confirm their roundness and size.

ED138 lives in that same far realm. Classed as a trans-Neptunian object, it orbits in the Kuiper Belt, the ring of icy bodies beyond Neptune left over from the solar system's formation. Astronomers suspect it formed much closer to the Sun before Neptune's gravity flung it into its wider, tilted orbit, now about 46 astronomical units from the Sun.

New Dwarf Planet Candidate 2026 ED138: How Big Is It?

The honest answer is that nobody knows yet. Based on ED138's distance, brightness and assumed surface reflectivity, the team estimates a diameter between 600 and 1,500 kilometres, or roughly 370 to 930 miles. At the lower end it would be the smallest dwarf planet yet observed; at the upper end it would be smaller than Pluto, Eris and Haumea but larger than Makemake and Ceres.

The uncertainty comes down to reflectivity: a bright, icy surface reflects more sunlight and so looks bigger than a dark, rocky one at the same distance. Astronomers cannot yet tell how much light ED138's surface bounces back, so its true size stays bracketed by that range. At roughly 1,000 kilometres across, an icy body that large should have enough gravity to pull itself round, the key test for dwarf planet status.

That is why the next observations matter so much. Infrared measurements, which sense the heat an object gives off rather than the sunlight it reflects, can break the size-versus-brightness deadlock. The James Webb Space Telescope is one candidate instrument for that work.

Reactions and Quotes

Holman, who made the discovery, was measured about what it means. "If confirmed as a dwarf planet, ED138 would join a very small family of worlds," he said at the announcement. He also put the find in historical perspective: "Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation."

Jurić, who verified the detection in Rubin's catalogues, stressed the telescope's role. "It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope," he said.

Pedro Bernardinelli, an astronomer at the University of São Paulo in Brazil, explained why scientists are confident the object is genuine rather than an artefact: "Given how big it is, it should be round, which is why we think it's a dwarf planet candidate."

Why It Matters

A new dwarf planet is more than a new name on a list. Each icy world beyond Neptune is a frozen time capsule from the solar system's birth, and its orbit is a record of the gravitational shoving match that arranged the planets. ED138's tilted, distant orbit points to an early close encounter with Neptune.

The discovery also matters as a proof of concept for Rubin Observatory itself. Jointly funded by the US National Science Foundation and the Department of Energy, the observatory sits on Cerro Pachón in central Chile with a 3,200-megapixel survey camera, and its mission is to photograph the entire southern sky every few nights for a decade. Finding a near-generation-scale object in pre-survey data suggests its outer solar system catalogue will be transformed within a few years.

What Happens Next

Confirmation comes in stages. First, astronomers will keep tracking ED138 to refine its orbit, using both new Rubin observations and further dives into archival survey images. A longer orbital arc sharpens predictions of where the object will be years from now.

Second, infrared observations will narrow the size estimate. If those measurements show a body large enough to be round, the case for dwarf planet status strengthens greatly. Finally, the International Astronomical Union would need to formally recognise ED138, a process that also involves giving it a proper name to replace the provisional 2026 ED138 designation. That naming step could take years.

Meanwhile, Rubin Observatory's main survey is only just beginning, and astronomers expect it to uncover many more trans-Neptunian objects, including further dwarf planet candidates.

Frequently Asked Questions

What is 2026 ED138?

2026 ED138 is a large, bright icy object orbiting beyond Pluto that scientists have identified as a dwarf planet candidate. It was found in Rubin Observatory data and announced by the International Astronomical Union Minor Planet Center on October 27, 2026.

How big is the new dwarf planet candidate?

Scientists estimate it is between 600 and 1,500 kilometres across. The wide range reflects uncertainty about how reflective its surface is; infrared observations are needed to measure its exact size.

Is 2026 ED138 officially a dwarf planet yet?

Not yet. It is a candidate. Confirmation requires measurements, probably in infrared light, showing it is large enough to be nearly round.

How far away is 2026 ED138?

It is currently about 46 astronomical units from the Sun, roughly 4.3 billion miles away. Pluto orbits at an average distance of about 40 astronomical units.

Why was it only discovered now?

ED138 hides in a crowded patch of sky near the plane of the Milky Way, where millions of stars can mask a faint moving object. Rubin's continuous sky survey and software that sifts billions of detections finally picked it out, and archive images later traced it back to at least 2016.

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