Astronomers have discovered a massive object in the outer Solar System that could become the sixth officially recognised dwarf planet. The object, named 2026 ED138, was identified using observations from the Vera C. Rubin Observatory in Chile and is estimated to measure between 600 and 1,500 kilometres across.
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The discovery was announced on October 27 by the International Astronomical Union's Minor Planet Center. Scientists believe the object could be among the largest dwarf planet candidates discovered beyond Neptune.
How was the mysterious object discovered?
Astrophysicist Matthew Holman of the Harvard-Smithsonian Center for Astrophysics spotted the object on October 13 while analysing data collected by the observatory earlier this year.
Holman was using software developed with colleague Kevin Napier to identify moving objects among billions of astronomical detections.
"My first reaction was one of excited disbelief," Holman said.
{{/usCountry}}"My first reaction was one of excited disbelief," Holman said.
{{/usCountry}}"Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong."
Further investigation revealed that the observatory had recorded the object 30 times across 20 nights between March 4 and July 11, 2026.
Researchers subsequently discovered something even more surprising. The object had appeared in archival images captured by the Dark Energy Camera as far back as February 2016, meaning evidence of its existence had remained unnoticed for more than a decade.
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What do scientists know about 2026 ED138?
The object is currently located approximately 46 astronomical units from the Sun, with one astronomical unit representing the average distance between Earth and the Sun.
According to a research paper, its orbit is tilted approximately 24.4 degrees relative to the Solar System's plane.
Scientists believe its position against the densely populated background of the Milky Way made it particularly difficult for earlier telescopes to detect.
Its exact diameter remains uncertain because astronomers have yet to determine how much sunlight its surface reflects.
However, its estimated size suggests that gravity may have shaped it into a roughly spherical body, a key requirement for dwarf planet classification.
Could more hidden worlds be discovered?
Further infrared observations will be needed to establish the object's actual size and determine whether it qualifies as a dwarf planet.
If confirmed, it would join Pluto, Ceres, Eris, Haumea and Makemake, the five dwarf planets officially recognised by the International Astronomical Union.
Scientists expect the Rubin Observatory's decade-long sky survey to uncover many more distant objects, potentially transforming our understanding of the Solar System's formation.
"Rubin will image the whole southern sky again and again for ten years," Holman said, "so any others hiding in the places earlier surveys skipped are now within reach."