Rubin observations reveal 2026 ED138, a large dwarf-planet candidate

Researchers have identified 2026 ED138 in observations from the Vera C. Rubin Observatory, adding a large candidate world to the known population of objects beyond Neptune. The International Astronomical Union’s Minor Planet Center announced it under the provisional designation 2026 ED138.

Its discovery emerged while Rubin was still being commissioned, before the observatory began its planned Legacy Survey of Space and Time. Astrophysicist Matthew Holman spotted the object while analyzing Rubin observations with software developed alongside colleague Kevin Napier.

The New York Post reports that the team traced it through 30 detections over 20 nights, spanning 4 March to 11 July 2026. Researchers also located it in older Dark Energy Camera images dating to February 2016, extending the observational record beyond Rubin’s newer data. The available size estimates are substantial but imprecise.

Jurić described ED138 as roughly 1,000 kilometers across and told GeekWire that finding an object of that scale may occur about once in a generation. Another account gives a wider estimated diameter range of 600 to 1,500 kilometers, explaining that uncertainty about surface reflectivity complicates the calculation. The New York Post says its size may rival Makemake and Haumea.

Those estimates do not settle whether ED138 qualifies as a dwarf planet. Universe Today describes it as an unconfirmed candidate and quotes Holman saying that confirmation would add it to a small group of worlds. The candidate label therefore reflects a possible classification, not a confirmed status.

Its provisional designation and detection are distinct from that unresolved classification. The object’s orbit offers another measure of its scale and distance. The Minor Planet Center’s figures put its orbital period at about 281 years, with its distance from the Sun ranging from 36.86 to 49.04 astronomical units.

A separate account compares Pluto’s average distance at 40 astronomical units; another gives Pluto’s orbital range as 29.6 to 49.08 astronomical units. These comparisons place ED138’s path in the outer Solar System, while showing that its closest and farthest points span a broad range.

Jurić characterized ED138 as the largest trans-Neptunian object found in about 20 years and said Rubin found it during telescope commissioning. That claim underscores the scientific significance researchers attach to the discovery, while the size range and outstanding dwarf-planet classification remain uncertain.

Rubin is expected to find more objects of this kind, and its planned survey will provide a larger body of observations for studying the distant Solar System.