Possible New Dwarf Planet: What Was Discovered Beyond Pluto’s Orbit?

TVS News AI, editorially supervised, presents Possible New Dwarf Planet: What Was Discovered Beyond Pluto’s Orbit.

Around 46 astronomical units from the Sun, a new celestial body is moving under the provisional designation 2026 ED138. According to initial analyses, the object could be among the largest and brightest bodies orbiting the Sun beyond Pluto’s orbit. ED138 is therefore a promising, though still unconfirmed, candidate for another dwarf planet.

The object was discovered by astronomer Matthew Holman of the Harvard-Smithsonian Center for Astrophysics in Cambridge. He analyzed data collected by the Vera C. Rubin Observatory in the same year. Using a search algorithm he developed himself, he sifted through billions of detections of moving objects. When ED138 appeared in the data, its brightness, combined with its distance, already indicated an unusual size.

Why Holman Initially Did Not Believe His Discovery

“My first reaction was joyful disbelief,” Holman said. “Objects like these are very rare, so I immediately checked whether I or the code had made a mistake.”

The rarity was his first reason to examine the finding critically. The team then searched archival images for additional images of ED138. This allowed its orbit to be traced over more than ten years. As a result, not only the object’s current position is known, but also a considerably longer section of its orbit.

The discovery itself

Holman did not find ED138 by directly looking at an already known celestial body. The search algorithm initially identified the object in the collected detections. It was the unusual combination of brightness and distance that led Holman to conclude that it might be larger. Additional verification using archived images subsequently confirmed that the same object had been observable for years.

Size and distance

ED138 is currently around 46 astronomical units from the Sun. One astronomical unit corresponds to the average distance between Earth and the Sun. Pluto lies at an average distance of 40 astronomical units. ED138 therefore orbits the Sun farther out than Pluto.

The Size Estimate Will Determine Its Classification

Whether an object qualifies as a dwarf planet depends primarily on its size and shape. The team estimates ED138’s diameter from its brightness, distance and estimated surface reflectivity at 600 to 1,500 kilometers.

The estimate therefore covers a considerable range. According to the statement, icy bodies of this size are generally round; a round shape is also a prerequisite for recognition as a dwarf planet. At 600 kilometers, the size estimate remains considerably less precise. At 1,500 kilometers, planetary scientist Ralf Jaumann of the Free University of Berlin considers ED138 a promising candidate.

Jaumann also pointed to the uncertainty of the calculation: “Of course, you can only estimate the size, and something between 600 and 1,500 kilometers is still a little imprecise.” For precisely that reason, no final classification can yet be derived from the current estimate.

The orbit is more precisely known than the size

In ED138’s case, the orbit is already relatively well known, Jaumann said. His observation: “It is already interesting that, using a telescope from Chile, you really do find an object out there, that you can also track it in this way and that you have already determined a large part of its orbit.”

ED138 therefore has a comparatively solid observational foundation. The decisive weakness, by contrast, is its estimated size. Its chances of official recognition will improve only if the object lies near the upper end of the range and actually has the required round shape.

Not Yet Confirmed as a Member of the Dwarf Planet Class

Unlike a dwarf planet, a planet has cleared its orbital path of small bodies. This distinction is crucial to the classification. According to the available information, ED138 is a promising candidate, but it is still not a confirmed dwarf planet.

The International Astronomical Union, abbreviated IAU, currently officially recognizes five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake. The most recent celestial body to be recognized as a dwarf planet was in 2008. Alongside the official objects, there are numerous other candidates, to which ED138 now belongs.

The IAU also introduced the dwarf planet class 20 years ago, when Pluto was renamed from planet to dwarf planet. ED138 would therefore not only add another object spatially beyond Pluto’s orbit to the class. It would also have to meet the astronomical requirements for a dwarf planet.

The current situation can therefore be clearly stated: ED138 has been discovered, its orbit has been traced over more than ten years and its diameter has been estimated at 600 to 1,500 kilometers. Whether it becomes an officially recognized additional dwarf planet will be decided by the still-unclear questions of its size and shape.