Rubin Observatory Finds Massive Dwarf Planet Candidate 2026 ED138 Beyond Pluto

Astronomers using the Vera C. Rubin Observatory have found an enormous candidate dwarf planet far beyond Pluto, an icy world provisionally named 2026 ED138 that could become the sixth officially recognised dwarf planet in the Solar System if further observations confirm its size. The object was picked out of observations collected earlier in 2026, and researchers say it may measure between 600 and 1,500 kilometres wide, which would place it among the largest bodies known in the outer Solar System.

The discovery was reported on October 30, 2026, and it offers an early glimpse of what Rubin Observatory’s decade-long survey of the southern sky could reveal. ED138 was found in a difficult patch of sky near the plane of the Milky Way, where millions of stars make moving objects hard to spot, and its location in the southern sky also made it difficult to observe from the Northern Hemisphere.

Why 2026 ED138 Is Still Only a Candidate

For now, ED138 remains a candidate rather than a confirmed dwarf planet, and the distinction matters. Scientists still need to establish the object’s physical size before confirming its classification, because brightness and distance alone suggest it is unusually large but do not settle the question. Matthew Holman, a Rubin Operations team member who discovered ED138, said that process would take further observations, probably a few months.

Holman identified the object while analysing Rubin data with a computer program that searches billions of detections of moving objects and matches observations that may belong to the same body. He said its brightness and distance suggested it was unusually large, and that his first response was excited disbelief, followed by checks for an error in the code or a false detection.

Its location in the southern sky also made it difficult to observe from the Northern Hemisphere, and its earlier invisibility was not simply a question of size.

To examine the finding, Holman worked with Mario Jurić, Rubin’s Solar System lead scientist. Jurić searched Rubin’s catalogue and found 20 additional observations of ED138 dating back to March 2026, and researchers also used other sources to trace its orbit as far back as 10 years. That long trail of observations helped confirm that the object was real and moving, rather than a glitch in a single night’s data.

How Large and How Far Away Is ED138?

Astronomers estimate ED138 is between 600 and 1,500 kilometres wide, or roughly 370 to 930 miles. It is currently about 46 astronomical units from the Sun, where one astronomical unit is the average distance between Earth and the Sun, while Pluto orbits at an average distance of about 40 astronomical units. In other words, ED138 is further out than Pluto, in the cold region beyond Neptune known as the trans-Neptunian region.

ED138 is a trans-Neptunian object, meaning it orbits beyond Neptune. Its orbit is tilted nearly 25 degrees from the plane of the Solar System, a feature astronomers say places it in the hot-classical trans-Neptunian object group. The tilt also suggests gravitational interactions with Neptune disturbed its original orbit, pushing it onto a path that is angled away from the flat disc where most planets travel.

That tilted, distant orbit is part of why the find is scientifically interesting. Objects in the outer Solar System carry clues about how the planets formed and how their gravity shaped the small bodies around them, and each large new object adds another data point to that history. A body as large as ED138 could be, if confirmed, would be a significant addition rather than a minor footnote.

Why It Stayed Hidden in a Crowded Sky

The candidate sits in a difficult patch of sky, and that difficulty explains part of its story. It was found near the plane of the Milky Way, where millions of stars crowd the view and make moving objects harder to spot. Telescopes and searches focused elsewhere could miss a moving object against such a dense field of stars, even when the object itself is large.

Rubin’s regular monitoring of the southern sky, combined with algorithms that sift through millions to billions of points of light, helped the team pick it out. Holman said people do not typically search for things in the Milky Way, because there are so many stars that it is really hard to find moving objects there. The discovery therefore shows not only a new object, but also a new capability: a survey that can watch the same crowded sky again and again, and connect observations made at different times into a single moving body.

The same kind of patient, repeated observation is driving progress elsewhere in space science. On Mars, for example, NASA’s Perseverance rover has measured ultrafine dust that could shape future astronaut suits and habitats, while new Earth-observation work such as Pixxel’s satellite contracts for defence and intelligence imagery shows how modern telescopes and satellites are turning repeated sky and Earth surveys into practical data. Rubin Observatory belongs to that same shift, from single snapshots to surveys that watch the sky change over time.

• Object: 2026 ED138, a dwarf planet candidate beyond Pluto
• Estimated size: between 600 and 1,500 kilometres wide
• Distance: about 46 astronomical units from the Sun, beyond Pluto’s average 40 astronomical units
• Orbit: trans-Neptunian, tilted nearly 25 degrees from the plane of the Solar System
• Discovery: found in Rubin Observatory data, with 20 additional observations dating back to March 2026 and an orbit traced back 10 years
• Status: still a candidate, pending confirmation of its physical size over the coming months
• Survey: detected while Rubin Observatory prepares for its 10-year Legacy Survey of Space and Time

What Rubin Observatory Could Find Next

The Vera C. Rubin Observatory detected ED138 while preparing for the Legacy Survey of Space and Time, a 10-year survey of the southern sky. Its ability to repeatedly capture changes across a wide area helped researchers identify the object and connect observations made at different times, and that same approach is expected to reveal more distant bodies.

Holman said there might be a handful of other objects around ED138’s size for Rubin to find. The candidate is also bright enough that capable amateur observers could see it if they know where to look, although it is not visible to the naked eye. Edward Ajhar, NSF Program Director for Rubin Observatory, said the telescope’s ability to capture movement among many objects would expand scientists’ understanding of the Solar System, the Milky Way and other galaxies.

If confirmed, ED138 would join the recognised dwarf planets Pluto, Ceres, Eris, Haumea and Makemake, becoming the sixth in that group. That confirmation, however, is not automatic, and researchers are careful to describe it as a candidate until its size is measured more precisely. The coming months of observation will decide whether the largest estimates hold, or whether ED138 turns out to be smaller than its brightness first suggested.

What to Watch Next

What to watch next is whether further observations confirm ED138’s physical size, whether it is formally classified as a dwarf planet, and whether Rubin’s survey turns up the handful of similarly sized objects its team expects to find in the outer Solar System. Those answers will come from patient follow-up observation, not from a single night’s data, and they will show how much of the distant Solar System is still waiting to be found in the crowded sky near the Milky Way.