Astronomers have identified a distant Solar System object that may qualify as a dwarf planet. Provisionally named 2026 ED138, it lies about 7.1 billion kilometers from the Sun and is the largest of roughly 2,300 objects beyond Pluto that the Vera C. Rubin Observatory has discovered, according to the observatory’s chief Solar System scientist, Mario Jurić.
The International Astronomical Union defines dwarf planets as bodies large enough for their gravity to make them round, but not massive enough to dominate their orbital neighborhoods. Because ED138 is too far away to observe its shape directly, its status remains uncertain.
The discovery came from images taken by Rubin between March and July. In individual frames, ED138 looked like a bright star. Software developed by astrophysicist Matthew Holman and colleague Kevin Napier linked its appearances across different nights, revealing that the point of light was moving and allowing the team to determine its orbit. The orbit is tilted by nearly 25 degrees relative to the planets’ orbits. Earlier images from other telescopes also showed the object, helping confirm the finding.
Based on its brightness, distance and assumptions about how much sunlight its surface reflects, Holman estimates that ED138 could be between 595 and 1,500 kilometers across. Icy bodies in the outer Solar System larger than about 400 kilometers are expected to be capable of becoming round, but observations have not yet established whether ED138 meets that test.
At the upper end of the estimate, ED138 would be comparable in size to Haumea and Makemake, both recognized dwarf planets. At the lower end, it would rank around 20th among the largest known dwarf planets and candidates. Pluto and Eris are considerably larger, each measuring more than 2,200 kilometers across.
The find does not provide evidence for or against the proposed Planet Nine, a hypothetical body some astronomers believe may orbit farther from the Sun. Holman said the discovery does show that objects remain to be found in the outer Solar System. He also suggested ED138 may have formed closer to the Sun, near Jupiter or Saturn, before a close encounter with a giant planet sent it outward.
Further observations could refine what is known about ED138. The James Webb Space Telescope may enable more detailed measurements, and finding a moon orbiting the object would help astronomers calculate the combined mass. As ED138 crosses a crowded region of sky, it may also pass in front of distant stars. Such events could provide a more precise estimate of its size and potentially clues about whether it has an atmosphere.
Sources: Folha Ciência.