Rubin Observatory spots a possible dwarf planet, 2026 ED138, beyond Neptune

The announcement came at a meeting of the American Astronomical Society's Division for Planetary Sciences in Spokane, Washington.

Matthew Holman, an astrophysicist at the Center for Astrophysics in Cambridge, Massachusetts, ran custom code across Rubin's records of moving objects and flagged the dot. The program, built with colleague Kevin Napier, sifts billions of detections for observations that might belong to the same body. Holman is also involved with Rubin Observatory operations. The search covered data collected between 4 March and 11 July 2026. Earlier observations from the Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile push the record back to 2016. That gives astronomers a longer baseline for its orbit.

Distance is the easy part. The object sits about 46 times farther from the Sun than Earth does, or roughly 4.3 billion miles out. Neptune orbits at about 30 times Earth's distance.

It is a trans-Neptunian object, one of the icy remnants left over from planet formation. Most such bodies sit in the Kuiper Belt, the donut-shaped region beyond Neptune. Dwarf planets are not confined there: Ceres sits in the asteroid belt between Mars and Jupiter, and Eris lies at the edge of the solar system.

Why the dwarf planet label matters

The International Astronomical Union recognizes five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake. The category dates from 2006, when the union set out what separates a planet from everything else. If 2026 ED138 is confirmed, it would be the first official addition to that list since the category was created. The criteria are demanding: an object must orbit the Sun, be massive enough for gravity to make it round, and have cleared its orbital neighbourhood of similar bodies. Pluto failed the third test. It was reclassified in 2006, a year after Eris turned up nearby. Astronomers describe 2026 ED138 as a candidate, not a member of the club.

What changes for readers is mostly symbolic. The official roster of worlds has not moved since the category was created. That is a matter of labels, not of the object itself.

It does not appear to be the long-theorized ninth planet, Vice reported. The closer comparison is with Haumea and Makemake, which sit in the same distant region. The comparison is about location and size, not about a hidden giant.

What the numbers say

Size estimates put the diameter between 600 and 1,500 kilometers, or roughly 370 to 930 miles. The range is wide because astronomers see reflected sunlight, not the object itself. A small body with a bright, reflective surface can look as luminous as a much larger dark one. Only a small number of known trans-Neptunian objects are intrinsically brighter, which is what makes this one such a promising candidate for a large distant world. At the top of the range it could rival Haumea and Makemake. Reports differ slightly on the orbit. One gives an inclination of about 24.4 degrees relative to the plane of the Solar System; another says about 25 degrees. Either way the object travels on a heavily tilted path compared with the planets. The gap is small and does not affect the classification.

Brightness is a proxy, not a measurement.

Rubin's opening act

The Rubin Observatory has only recently become fully operational. It is expected to discover an estimated 32,000 objects beyond Neptune's orbit over the next decade, many of them small and several of them dwarf planets. The 2026 ED138 detection came from data gathered while the observatory was preparing for its major long-term survey. Rubin's main survey has not yet begun. The first results are arriving before the main survey starts.

Paul Byrne, a planetary scientist at Washington University in St. Louis, told National Geographic that the find "heralds a new era of solar system and planetary science". Samantha Lawler, an astronomer at the University of Regina, said it was nice to have confirmation that the "giant, expensive, complicated machine is working". Byrne also said this part of the solar system is largely unknown, and that each detection brings researchers closer to understanding how planetary systems form. Both comments point at the same thing. A survey earns its keep on volume.

That estimate is the number to watch.

What happens next

Astronomers need better measurements of the object's physical size before anyone can confirm dwarf planet status. Telescopes that detect its thermal emission could settle the question of its dimensions. Thermal emission offers a way around the reflected-light problem. Scientists plan to use the James Webb Space Telescope and ALMA to examine its size and check whether it has moons. The question is physical, not positional.

Nothing is settled yet. If upcoming observations verify its size and round shape, it would join the five confirmed dwarf planets, each formally recognized by the International Astronomical Union. If they do not, 2026 ED138 stays a candidate. The classification depends on those follow-up measurements.

The union will have the final say on whether the object joins the list.