Astronomers have identified a large icy object beyond Pluto that could become the Solar System’s sixth officially recognised dwarf planet. Provisionally designated 2026 ED138, the object was discovered in data from the NSF–DOE Vera C. Rubin Observatory and may be one of the largest objects found in the distant Solar System in about two decades.
2026 ED138 has not yet been confirmed as a dwarf planet. Scientists need additional observations to determine its exact size and physical properties before its status can be established.
What is 2026 ED138?
2026 ED138 is a trans-Neptunian object (TNO)—a body that orbits the Sun beyond Neptune. It is currently about 46 astronomical units (AU) from the Sun. One AU is the average distance between Earth and the Sun, meaning ED138 is currently roughly 46 times farther from the Sun than Earth.
For comparison, Pluto’s average distance from the Sun is about 40 AU. Initial estimates suggest that ED138 could be between 600 and 1,500 kilometres in diameter.
That is a surprisingly large range, but it reflects an important problem – scientists can measure how bright the object appears, but its actual size depends partly on how much sunlight its surface reflects. If the larger estimates are correct, ED138 could rank among the largest dwarf-planet candidates known beyond Neptune.
Has a sixth dwarf planet been discovered?
Not yet. The International Astronomical Union (IAU) currently recognises five dwarf planets in the Solar System:
- Ceres
- Pluto
- Eris
- Haumea
- Makemake
For an object to qualify as a dwarf planet, it must orbit the Sun, have enough mass for its own gravity to make it approximately round, and not have cleared its orbital neighbourhood.
Scientists believe ED138 may be large enough to be round under its own gravity, but its exact size and physical characteristics still need to be established.
How was the possible new dwarf planet found?
On October 13, 2026, astrophysicist Matthew Holman was running data collected earlier in the year by the Vera C. Rubin Observatory through a search algorithm. The software compares billions of detections and looks for patterns showing that different points of light actually belong to the same moving object.
ED138 stood out because its apparent brightness was unusually high for an object at such a great distance. The team then searched Rubin’s observations for additional appearances of the object.
They found 20 more observations, giving a total of 30 Rubin observations across 20 nights between March 4 and July 11, 2026.
The object was hiding in old astronomical data
One of the most interesting parts of the discovery is that ED138 wasn’t completely invisible before 2026. Researchers searched archival observations and found the object in images going back to 2016.
Data from the Dark Energy Camera (DECam), combined with the Asteroid Institute’s ADAM Precovery service, helped scientists trace more than a decade of ED138’s movement through the Solar System.
Why did astronomers miss ED138 for so long?
ED138 lies close to the plane of the Milky Way, where the background is crowded with enormous numbers of stars. A faint, distant Solar System object moving slowly across such a dense background can easily get lost among the stars.
Rubin Observatory’s ability to repeatedly photograph the sky and use algorithms to identify movement helped separate ED138 from that crowded background.
This is what makes the discovery particularly significant. Rubin isn’t simply producing sharper pictures of space. It is repeatedly collecting huge amounts of data and using computational methods to find what has changed or moved.
What makes the Vera C. Rubin Observatory different?
The Vera C. Rubin Observatory, located on Cerro Pachón in Chile, was designed to repeatedly survey the southern sky. Its Simonyi Survey Telescope combines a large telescope with the world’s largest digital camera for astronomy, allowing researchers to capture enormous areas of the sky with high sensitivity.
The observatory’s decade-long Legacy Survey of Space and Time (LSST) officially began in 2026. The ED138 discovery came from observations taken during the period leading up to the main survey, showing the discovery potential of the system even before the full survey gets underway.
And ED138 is not Rubin’s first major Solar System discovery this year.
In April, the Rubin team submitted observations of more than 11,000 new asteroids to the International Astronomical Union’s Minor Planet Center. That submission included roughly 380 new trans-Neptunian objects.
How big is 2026 ED138 really?
The current estimate is 600–1,500 km across. Scientists need observations at infrared and longer wavelengths to better determine its size because reflected visible light alone cannot tell researchers exactly how large or reflective its surface is.
Follow-up observations, including potential observations with facilities such as ALMA, could help constrain its physical properties. Once scientists have a better estimate of its size, they will have a clearer idea of whether ED138 is massive enough to have become roughly spherical under its own gravity.
ED138 could eventually become the Solar System’s sixth recognised dwarf planet. But there is another story here.
A potentially kilometre-scale—or larger—world was sitting in astronomical images dating back years, hidden among millions of background stars. It took a new generation of telescope technology, repeated observations and algorithms capable of searching billions of detections to connect those faint points of light.
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