Astronomers using the Vera C. Rubin Observatory in Chile have discovered a large icy object beyond Pluto that may eventually be classified as a dwarf planet. The candidate, provisionally named 2026 ED138, is estimated to be between about 600 and 1,500 kilometers across and travels around the Sun at roughly 46 times Earth’s average orbital distance. If its size and shape are confirmed, it could become one of the largest known objects in the outer solar system.
The discovery came from Rubin’s enormous survey camera
The Vera C. Rubin Observatory was designed to repeatedly photograph large areas of the southern sky. Its camera can detect faint objects by comparing images taken at different times.
2026 ED138 was identified because it moved slightly against the background stars.
Its size is still uncertain
Astronomers estimate the object’s diameter from its brightness, but that method depends on how reflective its surface is. A bright icy body can appear larger or smaller depending on its albedo.
That is why the current size range remains broad.
Why it might qualify as a dwarf planet
The International Astronomical Union defines dwarf planets as bodies that orbit the Sun, are massive enough for gravity to make them roughly round, but have not cleared their orbital neighborhood.
If 2026 ED138 is near the upper end of the size estimate, it would almost certainly be round.
Pluto is the most famous member of the group
Pluto was reclassified as a dwarf planet in 2006, joining Ceres, Eris, Haumea and Makemake in the IAU’s recognized list.
The decision remains one of astronomy’s most widely discussed classification changes.
The object orbits farther out than Pluto
Pluto’s average distance from the Sun is about 40 astronomical units. The new candidate’s orbit lies around 46 astronomical units away.
At that distance, sunlight is weak and surface temperatures are extremely low.
Longer-wavelength observations are needed
Researchers hope to use facilities such as the Atacama Large Millimeter/submillimeter Array to measure the object’s thermal emission.
Combining heat measurements with visible brightness can provide a much better estimate of actual size.
Rubin Observatory is only beginning its survey
The observatory’s Legacy Survey of Space and Time is expected to catalog billions of stars and galaxies while also detecting moving objects throughout the solar system.
Astronomers expect it to transform the inventory of distant trans-Neptunian bodies.
The outer solar system remains poorly mapped
Objects beyond Neptune are faint, slow-moving and extremely distant. Many can take centuries to complete one orbit.
That makes repeated wide-field observations essential for discovering and tracking them.
The discovery could improve models of solar-system formation
The number, size and orbital distribution of distant icy bodies provide clues about how the giant planets migrated early in solar-system history.
Each new object adds another data point to those models.
There may be many more large bodies waiting to be found
Rubin’s sensitivity means researchers may discover additional dwarf-planet candidates over the next several years. Some could be smaller than Pluto, while others may challenge existing assumptions about the outer solar system.
The discovery of 2026 ED138 is therefore likely to be an early result rather than an isolated one.
Classification will take time
Scientists must refine the orbit, measure the object’s physical size and determine whether its gravity has made it round before formal classification.
For now, 2026 ED138 is a candidate, but it already demonstrates the discovery power of one of astronomy’s newest observatories.
Sources
- NSF–DOE Vera C. Rubin Observatory announcement
- U.S. National Science Foundation
- Reuters, Oct. 29, 2026
Its surface composition is another open question
Objects at this distance can contain mixtures of water ice, methane, nitrogen and darker organic material. Spectroscopic observations may eventually reveal which substances dominate the surface of 2026 ED138. Composition can help researchers connect the object to other populations in the Kuiper Belt and beyond.
Color and reflectivity will also improve estimates of its diameter because the current size range depends heavily on assumed brightness properties.
A formal dwarf-planet label is not automatic
Even if the object proves large enough to be round, the International Astronomical Union would still need sufficient observational evidence before adding it to the official list. Astronomers may spend years refining measurements before classification becomes formal.
That caution is normal in planetary science. The importance of the discovery does not depend on immediate naming status; its orbit and physical properties are already scientifically valuable.
