A dwarf planet candidate beyond Pluto has been identified in new observations from the Vera C. Rubin Observatory, giving astronomers a rare look at a large and distant world in the outer solar system. The object, provisionally designated 2026 ED138, is not an officially recognized dwarf planet yet, but scientists say it could eventually join Pluto and four other bodies in that category.
Rubin Observatory announced the discovery on October 27, 2026. Initial estimates suggest ED138 is between about 600 and 1,500 kilometers wide and currently lies roughly 46 astronomical units from the Sun. One astronomical unit is the average distance between Earth and the Sun. Pluto’s average distance is about 40 astronomical units, making ED138 more distant than Pluto at its present location.
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ED138 is classified as a trans-Neptunian object, or TNO, because it orbits beyond Neptune. TNOs include a wide range of icy bodies, from relatively small remnants left over from the solar system’s formation to objects large enough to be considered dwarf planet candidates.
The new object stands out because of its estimated size and brightness. Based on its distance, how much sunlight it reflects and assumptions about its surface reflectivity, researchers estimate that ED138 could be comparable in scale to some of the larger known dwarf planet candidates beyond Neptune. However, that estimate has a wide range, and its actual diameter has not been measured directly.
That uncertainty matters. A distant object can appear bright because it is relatively large, highly reflective or some combination of both. Infrared observations should help astronomers refine the estimate and learn more about the object’s physical properties.
Why ED138 is not officially a dwarf planet yet
The phrase “dwarf planet” is not simply a synonym for “large object beyond Neptune.” Under the International Astronomical Union’s definition, a dwarf planet must orbit the Sun, be massive enough for its own gravity to pull it into a nearly round shape, and not have cleared its orbital neighborhood. It also cannot be a moon.
Scientists believe icy bodies in ED138’s estimated size range are likely to be rounded by their own gravity. But likely is not the same as confirmed. Researchers still need better measurements of its size, reflectivity and composition before the object can be evaluated with greater confidence.
For now, ED138 has a provisional designation rather than an official dwarf planet name. If later observations establish that it meets the necessary criteria, it could become the sixth dwarf planet recognized by the IAU, joining Ceres, Pluto, Eris, Haumea and Makemake.
How the object remained hidden for so long
ED138 was not necessarily invisible to earlier telescopes. The bigger problem was where it appeared in the sky.
The object is located near the plane of the Milky Way, a region packed with background stars. A faint, slowly moving object can be difficult to separate from that dense field, especially when observations are made only occasionally. Rubin’s combination of repeated imaging, wide sky coverage and software designed to identify moving objects helped bring ED138 to light.
Matthew Holman, a Rubin Operations team member and astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, found the object while running a search code through billions of detections collected earlier in 2026. Further checks by Rubin Solar System lead scientist Mario Jurić uncovered additional observations, reducing the chance that the initial signal was an error.
Rubin observed ED138 30 times across 20 nights between March 4 and July 11, 2026. Researchers also found older images from the Dark Energy Camera that extend the observational record back to 2016. Those archival detections, sometimes called “precovery” observations, help astronomers calculate the object’s orbit more accurately.
What ED138 could reveal about the outer solar system
Finding a large object in this region is useful for more than expanding the list of possible dwarf planets. The distribution and orbits of TNOs preserve clues about how the solar system developed.
ED138’s orbit is tilted nearly 25 degrees relative to the solar system’s main plane. Rubin researchers classify it as a hot-classical TNO and say its path may have been altered by gravitational interactions with Neptune. Studying objects with unusual orbits can help scientists reconstruct how the giant planets moved and how smaller icy worlds were scattered during the solar system’s early history.
The discovery also demonstrates why repeated surveys matter. A single image may show only a faint point of light. A series of images taken over time can reveal motion, establish an orbit and make it possible to search older records for the same object.
What happens next
The immediate priority is follow-up observing. Infrared measurements could narrow ED138’s size range and provide a better indication of its surface properties. Continued tracking will also improve knowledge of its orbit and help researchers determine how it fits into the population of distant solar system bodies.
There is no indication that ED138 is a new major planet or a replacement for Pluto. The discovery concerns a possible dwarf planet, a smaller class of worlds that share their orbital neighborhoods with other objects. Pluto itself remains classified as a dwarf planet under the IAU’s 2006 definition.
Rubin’s Legacy Survey of Space and Time is expected to repeatedly scan the southern sky for a decade. That makes ED138 potentially more than an isolated discovery: it may be an early example of the distant objects the observatory will uncover as its survey continues.
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