Scientists using the Vera C. Rubin Observatory have identified 2026 ED138, a distant icy world estimated to measure 600 to 1,500 kilometers across. The discovery could expand the solar system’s five officially recognized dwarf planets to six.
Astronomers have discovered a large, distant object beyond Pluto that could become the sixth officially recognized dwarf planet in our solar system. The object, designated 2026 ED138, was identified using observations from the Vera C. Rubin Observatory in Chile, with the discovery announced on October 27, 2026.
Early measurements suggest the icy world measures between 600 and 1,500 kilometers (373 and 932 miles) across, making it one of the largest dwarf planet candidates discovered beyond Neptune. Scientists must gather more evidence before determining whether it meets the requirements for official classification.
The announcement marks an important discovery for the Rubin Observatory, which began its major sky survey earlier this year. The observatory’s powerful telescope and advanced computer systems are designed to detect faint objects that have escaped earlier searches.
How Astronomers Discovered 2026 ED138
The discovery began on October 13, when astronomer Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian examined observations collected by Rubin earlier in 2026.
Holman was using specialized software developed with colleague Kevin Napier to identify objects moving against the background of stars. The program compares billions of observations and searches for patterns that indicate the movement of distant objects through the solar system.
One object immediately stood out because of its unusual combination of brightness and distance.
“My first reaction was one of excited disbelief,” Holman said in the observatory’s announcement.
Holman initially questioned whether the result reflected a mistake in the observations or computer analysis. Follow-up checks supported the discovery, prompting researchers to search for additional images of the object.
University of Washington astronomy professor Mario Jurić examined Rubin’s records and identified 20 additional observations dating back to March 4, 2026.
In total, Rubin’s Simonyi Survey Telescope had observed ED138 30 times across 20 nights between March 4 and July 11, 2026.
Researchers also located older images captured by the Dark Energy Camera at Chile’s Cerro Tololo Inter-American Observatory. Those records extended back to 2016, allowing scientists to trace more than a decade of the object’s movement.
The International Astronomical Union’s Minor Planet Center announced the discovery on October 27. Holman and Jurić presented the findings that day at the 58th annual Division for Planetary Sciences meeting in Spokane, Washington.
A Large Icy World Beyond Pluto
ED138 currently lies approximately 46 astronomical units from the Sun. One astronomical unit represents the average distance between Earth and the Sun, approximately 150 million kilometers.
That places the newly discovered object about 6.9 billion kilometers, or 4.3 billion miles, from the Sun.
For comparison, Pluto orbits the Sun at an average distance of roughly 40 astronomical units. Neptune, the outermost recognized planet, has an average orbital distance of approximately 30 astronomical units.
Astronomers classify ED138 as a trans-Neptunian object, meaning it belongs to a broad population of bodies orbiting beyond Neptune.
Its orbit is tilted almost 25 degrees relative to the main plane of the solar system. This unusual inclination places it among objects known as hot-classical trans-Neptunian objects.
The word “hot” describes their orbital behavior rather than their temperature. These bodies follow more dynamically excited orbits than objects that remain close to the solar system’s main orbital plane.
Researchers believe gravitational interactions involving Neptune may have disturbed ED138’s original orbit billions of years ago.
Studying that movement could provide evidence about how the giant planets migrated during the solar system’s early development.
Why It Could Become the Sixth Dwarf Planet
The International Astronomical Union currently recognizes five dwarf planets: Ceres, Pluto, Eris, Haumea and Makemake.
Ceres orbits between Mars and Jupiter in the asteroid belt. The other four officially recognized dwarf planets occupy distant regions of the solar system beyond Neptune.
To qualify as a dwarf planet, an object must orbit the Sun, have enough mass for gravity to pull it into a nearly round shape, and not have cleared its orbital neighborhood of other objects. It also cannot be a natural satellite.
ED138 appears to meet several of those requirements, but astronomers have not yet established its exact size or shape.
The present size estimate depends on measurements of its brightness, distance and assumed surface reflectivity.
A bright object is not necessarily enormous. A smaller body with a highly reflective icy surface can appear as bright as a larger, darker object at the same distance.
This uncertainty explains why researchers currently estimate such a wide range for ED138’s diameter.
Infrared observations could help determine its actual size by measuring thermal radiation rather than relying entirely on reflected sunlight.
Scientists expect icy bodies within the estimated size range to be approximately round, but additional observations are needed to strengthen the case for dwarf planet status.
ED138 has not yet been officially classified as the solar system’s sixth dwarf planet.
Why Such a Large Object Remained Hidden
Despite its considerable estimated size, ED138 escaped earlier surveys because of its position against a particularly crowded section of the night sky.
The object appears close to the plane of the Milky Way, where millions of distant stars create a dense background of light.
For conventional surveys, separating a faint, slowly moving object from so many stationary background sources can be extremely difficult.
Rubin Observatory approaches the problem differently. Its exceptionally sensitive digital camera repeatedly photographs enormous sections of the southern sky, allowing scientists to compare observations taken at different times.
Computer algorithms identify tiny changes in position that may reveal asteroids, comets and other solar system bodies.
The technology makes it possible to discover objects that have appeared in previous astronomical images without being recognized.
ED138 demonstrates this capability. Once scientists identified it, they could locate earlier observations and improve calculations of its orbit.
Rubin Observatory Opens a New Era of Solar System Research
The Vera C. Rubin Observatory sits on Cerro Pachón in the Chilean Andes. It is jointly funded by the U.S. National Science Foundation and the Department of Energy’s Office of Science.
Its principal instrument, the Simonyi Survey Telescope, uses a 3,200-megapixel digital camera to survey the sky with exceptional detail.
The observatory’s Legacy Survey of Space and Time began in June 2026. Over 10 years, the project will repeatedly photograph the southern sky and create an extensive record of changes throughout the universe.
The project is expected to improve research into asteroids, distant solar system bodies, galaxies, dark matter and dark energy.
Its early findings have already demonstrated the telescope’s ability to identify previously unknown objects.
In April 2026, the Rubin team submitted observations of more than 11,000 new asteroids to the Minor Planet Center. Approximately 380 were trans-Neptunian objects.
The discovery of ED138 suggests that even relatively large bodies may remain undetected in sections of the sky that earlier surveys could not examine effectively.
Researchers are particularly interested in what these objects reveal about the solar system’s formation approximately 4.6 billion years ago.
Distant icy bodies can preserve evidence of ancient conditions and gravitational disturbances that shaped the planets’ present-day orbits.
Their positions, sizes and orbital characteristics help scientists test models of how Neptune and the other giant planets moved after forming.
What Happens Next for ED138?
Astronomers will continue monitoring ED138 and seek additional observations from other telescopes.
Infrared measurements are particularly important because they could narrow the estimated diameter and help determine whether the object has the rounded shape expected of a dwarf planet.
Researchers will also refine its orbit and investigate its physical properties.
The public can explore a visualization of ED138’s orbital path through Orbitviewer, an interactive application that displays solar system objects in three dimensions.
For now, the newly discovered body remains a promising candidate rather than an officially recognized dwarf planet. Its identification shows that even after centuries of astronomical observations, sizable unexplored worlds may still be hiding beyond Neptune.
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