Astronomers have found a large, icy world far beyond Pluto that could one day join the small family of dwarf planets. For now, it is only a candidate. Its temporary name is 2026 ED138, and scientists say more work is needed before anyone can call it a dwarf planet for sure.
The discovery was announced on October 27, 2026, by the NSF–DOE Vera C. Rubin Observatory in Chile. The International Astronomical Union Minor Planet Center announced the observations the same day, and the team presented the results at a meeting of the American Astronomical Society’s Division for Planetary Sciences in Spokane, Washington.
Here is the key point to keep in mind as you read: “candidate” is not a small detail. It is the whole story. The object is real, its orbit has been traced back over more than 10 years, and its size suggests it could be round. But until follow-up observations pin down its exact size, scientists cannot say it meets the full definition of a dwarf planet.
What we know / What we don’t know
What we know:
- The object, provisionally named 2026 ED138, was found in data from the Rubin Observatory’s Simonyi Survey Telescope in Chile.
- It was first spotted on the evening of October 13, 2026, by Matthew Holman, a senior astrophysicist at the Center for Astrophysics, Harvard and Smithsonian, using search software he developed with colleague Kevin Napier.
- Rubin observed it 30 times on 20 nights between March 4 and July 11, 2026, and older telescope images trace it back to 2016 — more than 10 years of orbit data in total.
- It is currently about 46 astronomical units (AU) from the Sun, where 1 AU is the average distance between Earth and the Sun. Pluto averages about 40 AU.
- Based on its brightness, distance, and assumed reflectivity, the team estimates it is between 600 and 1,500 kilometers (about 370 to 930 miles) across.
- Its orbit is tilted almost 25 degrees off the plane of the solar system, which suggests it was nudged by gravitational interactions with Neptune in the distant past.
- It was hiding in a crowded patch of sky near the plane of the Milky Way, where millions of stars made it hard to spot.
- The Rubin Observatory is jointly funded by the U.S. National Science Foundation and the U.S. Department of Energy, and its 10-year Legacy Survey of Space and Time began in June 2026.
What we don’t know:
- Whether 2026 ED138 is truly round. A dwarf planet must be massive enough for its own gravity to pull it into a round shape, and that has not been proven yet.
- Its exact size. The 600 to 1,500 kilometer range is wide because scientists do not yet know how reflective its surface is. Infrared observations are needed to narrow it down.
- What it is made of, what its surface looks like, or whether it has moons. None of that has been measured yet.
- When, or even whether, the International Astronomical Union will formally recognize it. One researcher quoted in coverage of the announcement said confirming its size will probably take a few months.
How a world this big stayed hidden
It sounds strange that something possibly as wide as 1,500 kilometers could go unnoticed until 2026. The answer is distance, faintness, and a very crowded background.
2026 ED138 sits in a part of the sky close to the plane of the Milky Way. To most telescopes, it was lost among millions of background stars. It moves slowly, it is faint, and earlier surveys were not built to pick a slow-moving speck out of that kind of crowd night after night.
Rubin changed that in two ways. It scans the southern sky over and over, and its software sifts through billions of detections of moving objects and links the ones that belong to the same body. Holman was running Rubin data from earlier in 2026 through that kind of search code when ED138 turned up.
His first reaction, in his own words, was “excited disbelief.” He said objects like this are very rare, so he immediately checked whether he or the code had made a mistake. The checks held.
Then Mario Juric, a University of Washington professor who leads Rubin’s solar system team, searched Rubin’s catalogs and found 20 more observations going back to March 2026. Archival images from the Dark Energy Camera, found through the Asteroid Institute’s precovery service, pushed the record back to 2016. Together, those sightings let the team trace more than a decade of its orbit.
What makes something a dwarf planet?
The word “planet” gets used loosely in everyday talk, but astronomers use a stricter test. A dwarf planet orbits the Sun, is not a moon, has not cleared its neighborhood of other objects, and — the part that matters here — is massive enough for its own gravity to shape it into a nearly round ball.
That last test is why size matters so much. Small, lumpy rocks do not count. Big, icy bodies usually do become round under their own gravity, and the team says icy bodies in ED138’s estimated size range are expected to be round. Expected, though, is not the same as measured.
Right now the size estimate itself is uncertain. Scientists judge size from how bright the object looks, how far away it is, and how much light its surface reflects. If the surface is dark, the object must be bigger to look as bright as it does. If it is bright and reflective, it could be smaller. That unknown — called albedo — is why the estimate spans 600 to 1,500 kilometers instead of giving one number.
Infrared observations can help because they measure heat, not just reflected sunlight, and that gives a much better handle on size. Until those observations come in, ED138 stays a candidate.
If it is confirmed, it would join only five worlds currently recognized by the International Astronomical Union as dwarf planets: Pluto, Ceres, Eris, Haumea, and Makemake. Ceres sits in the asteroid belt between Mars and Jupiter. The other four orbit beyond Neptune. ED138 would be the sixth, and by the team’s early analysis, among the largest ever found beyond Neptune.
Why this discovery matters even before confirmation
You do not need to wait for a formal label for this find to be important. It tells us something simple and striking: our map of the outer solar system is still incomplete.
Rubin only began its main 10-year survey in June 2026. Before that survey formally started, its solar system team had already submitted observations of more than 11,000 new asteroids to the Minor Planet Center, including roughly 380 new objects beyond Neptune. ED138 is the first dwarf planet candidate from that flood of data.
“If confirmed as a dwarf planet, ED138 would join a very small family of worlds,” Holman said in the observatory’s announcement. “Rubin will image the whole southern sky again and again for 10 years, so any others hiding in the places earlier surveys skipped are now within reach.”
Juric put it in similar terms, saying Rubin gives astronomers an unprecedented ability to explore the sky through speed, depth, and precision, and that the ability to search back through months or even decades of old images is changing how quickly and accurately orbits can be worked out.
That matters for science, not just for lists. Objects beyond Neptune are leftovers from how the solar system formed and how the giant planets moved long ago. Their orbits — including ED138’s steep 25-degree tilt — carry clues about past gravitational nudges from Neptune.
What happens next
The next steps are straightforward, and none of them are instant.
First, astronomers around the world can now organize follow-up observations, since the discovery has been announced through the Minor Planet Center. Infrared measurements are the priority because they will narrow the size range and test whether the body is round enough to qualify.
Second, Rubin will keep watching. Its survey photographs the southern sky repeatedly for a decade, so ED138 will be picked up again and again, and its orbit will get more precise over time. The public can also explore its orbit through the interactive Orbitviewer tool linked from the observatory’s announcement.
Third, if the size checks out, the question goes to the International Astronomical Union, which decides formal classifications. That process does not happen overnight, and the announcement itself promises no outcome. Until then, every accurate headline should say “candidate.” Follow our science and tech coverage for updates as the follow-up observations come in.
For everyday readers, one practical point: you cannot go outside and see ED138. It is far too faint, and it was found in telescope data, not by looking up. If you enjoy explainers like this one, we also break down everyday science close to home, like why king tides flood Southern California streets.
The honest summary is this: astronomers have found a genuinely large, genuinely interesting world beyond Pluto, traced it back through a decade of images, and shown it is a strong dwarf planet candidate. Whether it earns the title is a question for the next round of observations, probably months away. What is already certain is that the telescope that found it has only just started its 10-year watch — and ED138 is unlikely to be its last surprise.
Sources: NSF–DOE Vera C. Rubin Observatory announcement, “NSF–DOE Vera C. Rubin Observatory Reveals Its First Dwarf Planet Candidate in Our Solar System,” October 27, 2026 (primary source); Reuters, “Possible new dwarf planet identified orbiting beyond Pluto,” October 28, 2026; CNN, October 28, 2026; University of Washington News, October 27, 2026. 2026 ED138 is a dwarf planet candidate, not a confirmed dwarf planet; size, shape, and composition remain unconfirmed. Corrections check on October 28, 2026 found no correction or retraction of the announcement.
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