‘Excited Disbelief’: New Dwarf Planet Candidate Spent Years Lost In A Crowd Of Stars

For about a decade, a distant world possibly hundreds of miles across has been showing up in telescope images of the outer solar system without anyone noticing it.

Now a new observatory in Chile has picked it out of the crowd. NSF–DOE Vera C. Rubin Observatory has found its first dwarf planet candidate, an object designated 2026 ED138 that currently lies beyond the orbit of Pluto. Early estimates suggest it may rank among the largest dwarf planet candidates ever discovered past Neptune.

If follow-up observations confirm it, ED138 would join a very short list. Only five objects carry official dwarf planet status from the International Astronomical Union: Pluto, Ceres, Eris, Haumea, and Makemake. Word of the discovery came from the IAU’s Minor Planet Center on October 27.

Finding a Dwarf Planet Candidate in Billions of Detections

Matthew Holman, a senior astrophysicist at the Center for Astrophysics | Harvard & Smithsonian (CfA), made the find on the evening of October 13. He was running Rubin data collected earlier in 2026 through a search program he built with CfA colleague Kevin Napier. Their code combs through billions of detections of moving objects and compares them to work out which specks of light belong to the same body.

One result stood out right away. Its brightness and distance pointed to something unusually large.

“My first reaction was one of excited disbelief,” Holman says in a statement. “Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.”

To rule out a mistake, Mario Jurić, Rubin’s Solar System lead scientist at the University of Washington, searched Rubin’s catalogs and images and turned up 20 more observations dating back to March 4, 2026. In all, Rubin’s Simonyi Survey Telescope caught ED138 30 times across 20 nights between March 4 and July 11. Archival images from the Dark Energy Camera in Chile, found through the Asteroid Institute’s ADAM Precovery service, stretched the record back to 2016, letting the team trace more than 10 years of ED138’s orbit.

A Tilted Orbit Beyond Pluto

ED138 currently sits about 46 astronomical units from the Sun. One astronomical unit equals the average distance between Earth and the Sun (roughly 93 million miles), which puts ED138 about 4.3 billion miles away. Pluto, by comparison, orbits at an average distance of 40 astronomical units. That placement makes ED138 a trans-Neptunian object, or TNO, the term for anything orbiting the Sun farther out than Neptune.

Its orbit also stands out for its angle. ED138’s path is tilted almost 25 degrees from the plane of the solar system, which classifies it as a hot-classical TNO. That steep tilt hints that Neptune’s gravity knocked it off the path it first followed.

Sizing Up Rubin’s Dwarf Planet Candidate

Plenty of objects orbit past Neptune, but only some qualify as dwarf planet candidates. To count as a dwarf planet, an object must be massive enough that its own gravity has squeezed it into a ball.

Using ED138’s distance, brightness, and estimated surface reflectivity (a property astronomers call albedo), the team estimates it measures between 600 and 1,500 kilometers across, or roughly 370 to 930 miles. An icy body of that size should be round. Because the reflectivity figure is an estimate rather than a measurement, the size range is wide, and infrared observations will be needed to pin down ED138’s size and confirm whether it truly is a dwarf planet.

Lost in a Crowded Patch of Sky

ED138’s location helps explain how something this big went unnoticed. It sits in a part of the sky near the Milky Way’s plane, where millions of stars crowd the view. Researchers say that dense background likely kept other telescopes from singling it out.

Rubin keeps returning to the whole Southern Hemisphere sky on a steady schedule, and its software checks enormous numbers of light sources to pick out the few that move like small solar system bodies.

“Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision,” says Jurić.

ED138 joins a fast-growing pile of Rubin discoveries. In April, before the Legacy Survey of Space and Time formally began in June 2026, the Rubin Solar System team submitted observations of more than 11,000 new asteroids to the Minor Planet Center, roughly 380 of them new TNOs.

“Rubin will image the whole southern sky again and again for ten years, so any others hiding in the places earlier surveys skipped are now within reach,” says Holman.

For now, ED138 remains a candidate whose final verdict depends on infrared follow-up. But with nearly a decade of sky-scanning still ahead, the solar system’s short list of dwarf planets may not stay short for long.