Astronomers have identified 2026 ED138, a large, icy object orbiting beyond Neptune that could become one of the largest recognized dwarf planets in the Solar System. Discovered in data from the NSF–DOE Vera C. Rubin Observatory, the object is estimated to be between 600 and 1,500 kilometers in diameter and currently lies about 46 times farther from the Sun than Earth does. Scientists have designated it a dwarf planet candidate, but additional observations are needed to determine its true size and whether it meets the requirements for that classification.
The discovery was announced on October 27, 2026, after researchers identified the object in observations collected earlier in the year. Its unusual brightness suggests that it may be significantly larger than many other objects in the distant Solar System. The finding also demonstrates the potential of the Rubin Observatory’s wide-field survey to reveal previously overlooked worlds in the Kuiper Belt and other regions beyond Neptune.
Key Takeaways
- New discovery: Astronomers identified 2026 ED138 in data collected by the Vera C. Rubin Observatory.
- Potential dwarf planet: Its estimated diameter ranges from approximately 600 to 1,500 kilometers.
- Extreme distance: It orbits around 46 astronomical units from the Sun, farther away than Pluto’s average distance.
- Unusual orbit: Its orbital inclination is approximately 24.4 degrees relative to the plane of the Solar System.
- Not officially classified: Scientists need better measurements of its physical size before confirming its dwarf planet status.
- Future observations: Telescopes capable of detecting the object’s thermal emission could help resolve uncertainties about its dimensions.
What Is 2026 ED138?
2026 ED138 is a trans-Neptunian object, meaning it orbits the Sun beyond Neptune. These distant bodies occupy a cold region of the Solar System that contains icy remnants left over from planetary formation.
The object has attracted attention because of its brightness. Only a small number of known trans-Neptunian objects are intrinsically brighter, making ED138 an unusually promising candidate for a large distant world.
The discovery was made by Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian, who is also involved with Rubin Observatory operations. Holman used a computer program developed with colleague Kevin Napier to search through billions of detections of moving objects and identify observations that might belong to the same celestial body.
The search revealed ED138 in data collected between March 4 and July 11, 2026. Further examination of the observatory’s records confirmed additional sightings, helping researchers establish its orbit.
Scientists also found earlier observations from the Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile. Those observations extend the object’s observational record back to 2016, giving researchers a longer baseline for studying its movement.
According to the Rubin Observatory announcement, the discovery emerged from data gathered while the observatory was preparing for its major long-term survey.
How Large Is the Newly Discovered Object?
The estimated diameter of 2026 ED138 ranges from approximately 600 to 1,500 kilometers. That wide range reflects an important difficulty in studying distant objects: astronomers often observe reflected sunlight rather than measuring an object’s physical dimensions directly.
A relatively small object with a bright, reflective surface can appear as luminous as a much larger object with a darker surface. Without knowing how much sunlight the surface reflects, researchers cannot determine the diameter precisely from brightness alone.
| Property | Current estimate or status |
|---|---|
| Provisional designation | 2026 ED138 |
| Object type | Trans-Neptunian object |
| Estimated diameter | 600–1,500 km |
| Current distance from the Sun | Approximately 46 AU |
| Orbital inclination | Approximately 24.4 degrees |
| Discovery data | Vera C. Rubin Observatory |
| Dwarf planet status | Candidate; not yet confirmed |
One astronomical unit, or AU, is the average distance between Earth and the Sun, approximately 150 million kilometers. At 46 AU, ED138 is therefore more than 6.8 billion kilometers from the Sun.
If future measurements place it near the upper end of the estimated size range, it could be among the largest dwarf planet candidates known beyond Neptune.
Why Scientists Think It Could Be a Dwarf Planet
A dwarf planet is a body that orbits the Sun, has sufficient mass for its own gravity to pull it into an approximately round shape, has not cleared its orbital neighborhood of other objects, and is not a natural satellite.
ED138’s estimated dimensions make it a plausible candidate. However, scientists have not yet established its exact physical size, shape or composition.
The distinction matters because a large asteroid or irregular icy body does not automatically qualify as a dwarf planet. Researchers need sufficient evidence to determine whether the object is massive enough for gravity to have shaped it into a rounded body.
The International Astronomical Union currently recognizes five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake. Ceres lies in the asteroid belt between Mars and Jupiter, while the other four orbit in the outer Solar System.
If ED138 is confirmed as a dwarf planet, it would join this small group. It would not become a newly discovered major planet, and the designation would not change the existing classification of Neptune as the Solar System’s outermost major planet.
Where Is 2026 ED138 Located?
The object currently orbits the Sun at a distance of roughly 46 AU, compared with Pluto’s average distance of approximately 40 AU.
ED138’s orbit is also tilted by around 24.4 degrees relative to the plane in which most planets orbit. This makes its path more inclined than the orbits of the major planets.
Researchers believe gravitational interactions with Neptune may have contributed to its unusual orbital configuration. Such interactions can change the paths of smaller bodies over long periods, scattering them into more distant or inclined orbits.
The object is part of the broader population of trans-Neptunian bodies that preserves evidence of the Solar System’s early history. Studying their positions, sizes and orbital patterns can help scientists understand how the giant planets migrated and how gravity redistributed icy material during the Solar System’s formation.
How the Vera C. Rubin Observatory Found It
The discovery highlights the capabilities of the Vera C. Rubin Observatory, located on Cerro Pachón in Chile. Its large telescope and 3.2-gigapixel camera are designed to repeatedly survey wide areas of the sky and detect objects that move or change brightness.
Rather than relying only on observations of known celestial bodies, researchers can analyze enormous datasets to identify objects that earlier surveys missed.
Holman’s search software compared detections across Rubin’s observations to identify the moving object now designated ED138. Additional observations helped confirm that the detections represented a real body rather than a data-processing error.
The observatory’s long-term Legacy Survey of Space and Time is designed to repeatedly image the southern sky over a period of about 10 years. This repeated coverage is expected to improve the inventory of asteroids, trans-Neptunian objects and other bodies in the Solar System.
ED138 is an early example of the discoveries that can emerge when large astronomical datasets are combined with specialized computational searches.
What Astronomers Still Need to Learn
Despite the discovery, several questions remain unanswered.
The first is the object’s physical diameter. Researchers hope that observations at longer wavelengths, including those possible with the Atacama Large Millimeter/submillimeter Array (ALMA), will help measure heat emitted by the object. Thermal measurements can help distinguish a small, reflective body from a larger, darker one.
Scientists also need to investigate its surface properties, composition and shape. At present, there is not enough evidence to conclude that ED138 has a surface resembling Pluto’s or that it possesses features such as nitrogen glaciers.
Its orbital characteristics will also benefit from continued observation. More precise measurements can improve estimates of its trajectory and clarify whether it participates in a particular orbital resonance with Neptune.
These uncertainties are normal in the early stages of studying a newly identified distant object. Its provisional designation reflects that the research is ongoing.
The Bigger Picture
The discovery of 2026 ED138 demonstrates that the outer Solar System still contains large objects that have escaped clear identification. The region beyond Neptune is populated by icy bodies that preserve clues about the conditions under which the planets formed and evolved.
Finding another potentially large dwarf planet would help astronomers refine estimates of how many such worlds exist and how they are distributed. It would also strengthen the case for systematic sky surveys that can detect objects hidden in crowded or difficult-to-observe regions.
The Rubin Observatory’s contribution extends beyond this single discovery. As its survey collects more observations, astronomers expect to identify additional moving objects and reconstruct their orbits with greater precision. The resulting data could reshape scientific understanding of the Solar System’s distant population.
FAQs
1. What is 2026 ED138?
2026 ED138 is a large trans-Neptunian object discovered in observations from the Vera C. Rubin Observatory. It is a candidate dwarf planet because its estimated size suggests it may be large enough for gravity to make it approximately round.
2. How big is 2026 ED138?
Its estimated diameter ranges from about 600 to 1,500 kilometers. Scientists need additional measurements to narrow the range.
3. Is 2026 ED138 officially a dwarf planet?
No. It is currently a dwarf planet candidate. Its physical size and ability to meet the dwarf planet criteria still need to be established.
4. How far is 2026 ED138 from Earth?
The object is currently about 46 astronomical units from the Sun. Its exact distance from Earth varies as both Earth and ED138 move along their orbits.
5. Could astronomers discover more dwarf planets?
Yes. The Rubin Observatory’s long-term survey is designed to find many previously unknown Solar System objects. Further observations may reveal additional large trans-Neptunian bodies, although not every discovery will qualify as a dwarf planet.
Looking Ahead
The immediate priority for astronomers is to measure ED138’s physical size more accurately and determine whether it is massive enough to be classified as a dwarf planet. Thermal observations and continued tracking will help researchers establish its characteristics and refine its orbital model. Until then, it remains a promising candidate rather than a confirmed addition to the Solar System’s dwarf planet population.
The discovery also offers an early indication of what large-scale astronomical surveys can achieve. As Rubin continues collecting data, researchers will have more opportunities to find distant worlds, test theories about planetary migration and improve the Solar System’s inventory. ED138 may eventually join the recognized dwarf planets, but even before that confirmation, it provides a valuable new target for studying the icy frontier beyond Neptune.
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