Rubin Telescope Spots Possible Sixth Dwarf Planet Beyond Pluto

The Vera C. Rubin Observatory in Chile has spotted a distant object that could become the sixth officially recognized dwarf planet in the solar system. Temporarily designated 2026 ED138, it orbits beyond Neptune and Pluto and may be among the largest and brightest bodies found in that region, according to USA Today and Live Science.

The object is now under consideration by the International Astronomical Union's Minor Planet Center, the global authority on classifying celestial bodies, USA Today reported, citing an Oct. 27 press release. Astronomers say more observations are needed before it can be confirmed.

How a hidden world was found

According to Live Science, 2026 ED138 orbits the sun at roughly 46 times the distance between Earth and the sun. Its orbit is tilted 25 degrees from the plane of the solar system, which put it in just the right position to be lost in the glow of the inner Milky Way, the researchers said. Many telescopes struggle to see past the millions of stars in the galaxy's central bulge.

Rubin images the entire southern sky every few nights with the largest digital camera ever built, Live Science reported, and it sends out millions of nightly alerts about objects that change brightness or position. That makes it well suited to finding anything that moves. USA Today said observations across 20 nights between March 4 and July 11 helped scientists confirm what they were seeing.

Astrophysicist Matthew Holman, who works on the observatory's data-processing software, wrote code with colleague Kevin Napier that compares billions of observations to work out which ones show the same moving object. Running Rubin data through it revealed the unusually large body. Holman said his first reaction was “excited disbelief,” and that he checked whether he or the code had made a mistake because such objects are very rare.

Live Science reported that the team also used earlier Rubin data and archival images from the Dark Energy Camera on the Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, also in Chile. With those, they mapped the object's orbit over the past 10 years.

How big is it, and is it a dwarf planet?

The size of 2026 ED138 is not measured directly. Researchers inferred it from the object's brightness, its surface reflectivity (albedo) and its distance from the sun. The estimate is a diameter between 370 and 930 miles (600 to 1,500 kilometers), a wide range. For comparison, Live Science put Pluto at 1,477 miles (2,377 km) across and Ceres, the smallest dwarf planet recognized by the astronomical union, at 595 miles (958 km). The upper end of the estimate is more than half of Pluto's diameter.

The commonly accepted definition says a dwarf planet has enough mass for its own gravity to pull it into a round shape, but not enough to clear debris from its orbital neighborhood. USA Today reported that icy bodies in the size range estimated for this object are expected to be round. Live Science said future observations should give a better picture of its diameter and density, which will help show whether it is round enough to qualify.

Five dwarf planets are currently recognized by the astronomical union: Pluto, Ceres, Eris, Haumea and Makemake. Reuters reported, as cited by USA Today, that Ceres is in the main asteroid belt between Mars and Jupiter, while the other four orbit beyond Neptune. Live Science noted that astronomers who study these worlds often recognize at least nine, with more candidates whose properties remain unknown.

Why it matters for the picture of the outer solar system

This find does not change anything in daily life, but it adds to the map of the solar system. Live Science described the Kuiper Belt, the region beyond Neptune stretching roughly 30 to 50 times the Earth-sun distance, as home to most known dwarf planets. Its small, icy bodies can act as frozen time capsules with clues about how the early solar system formed.

The discovery also shows what the new observatory can do so early in its work. The National Science Foundation jointly funds and operates Rubin with the Department of Energy's Office of Science, according to USA Today. Live Science said the observatory began its 10-year survey in July.

Holman said in a statement that if confirmed, 2026 ED138 would join a “very small family of worlds.” He added that because Rubin will image the whole southern sky repeatedly over 10 years, any others hiding in places earlier surveys skipped are now within reach.

What happens next

The Minor Planet Center is reviewing the object, and astronomers plan further observations to pin down its size and shape. No date for a decision has been given in the reports.

Around Prague, based on reporting by USA Today, Live Science