Rubin Observatory Detects Dwarf Planet Candidate Beyond Pluto

Astronomers have identified a possible dwarf planet beyond Pluto’s orbit using observations from the Vera C. Rubin Observatory in Chile, CNN reported.

Provisionally named ED138, the object has an estimated diameter of between 600 and 1,500 kilometres. Its physical size remains uncertain, and it has not been officially recognised as a dwarf planet, according to CNN.

The discovery began when Matthew Holman, a Smithsonian senior astrophysicist and astronomy lecturer at Harvard University, searched Rubin data collected earlier in 2026. He used a computer programme he helped develop to examine billions of detections of moving objects.

Holman, who also works with the Rubin Operations team, initially checked whether the detection could be a false positive or a software error, CNN reported.

He then worked with Mario Jurić, Rubin’s Solar System lead scientist and an astronomy professor at the University of Washington. Jurić located 20 additional observations in Rubin’s catalogue dating back to March 2026. Using other sources, the researchers eventually traced the object’s orbit back 10 years.

According to CNN, ED138 currently lies about 46 astronomical units from the sun. An astronomical unit represents the average distance between Earth and the sun.

Its location places it among trans-Neptunian objects, which orbit the sun beyond Neptune. ED138 is too faint to see without equipment, although Holman said sufficiently capable amateur astronomers could observe it if they knew where to look.

Several circumstances helped the object escape earlier detection, CNN reported. Its position in the southern sky makes observation difficult from the northern hemisphere, excluding many telescopes from the search.

It has also appeared against the crowded background of the Milky Way. Holman explained that, from Earth’s perspective, ED138 had spent the past 20 years moving across that region, where large numbers of stars make moving objects harder to distinguish.

Rubin began operating in 2025 and houses the world’s largest digital camera, according to CNN. The observatory stands on a mountain 2,682 metres high and can image the entire sky every three days.

The candidate adds to Rubin’s detections of asteroids and smaller trans-Neptunian objects. Megan Schwamb, an astrophysicist at Queen’s University Belfast and a member of Rubin’s Solar System Operations team, told CNN she was surprised that such a large object emerged so early in the observatory’s commissioning observations.

The distinction between a candidate and a confirmed dwarf planet remains important. CNN reported that the International Astronomical Union recognises five dwarf planets: Ceres, Pluto, Haumea, Makemake and Eris.

Under the definitions adopted in 2006, dwarf planets are nearly round objects orbiting the sun that have not cleared their orbital neighbourhoods of debris. Pluto’s classification changed because it did not meet that orbit-clearing requirement, CNN explained.

ED138’s estimated size range would place it above Ceres, the smallest recognised dwarf planet. Holman nevertheless stressed that establishing its actual physical size is necessary before its status can be settled.

Michele Bannister, an associate professor at the University of Canterbury who was not involved in the discovery, told CNN that the object’s combination of substantial size and distant orbit makes it scientifically significant.

Further telescope observations will investigate its physical properties. According to CNN, confirmation as a dwarf planet would be followed by a permanent number and a name, through a process whose timing and naming arrangements remain unsettled.

Sources

• ‘It’s big’: Astronomers make startling discovery of a possible dwarf planet beyond Pluto