Astronomers using the Vera C. Rubin Observatory in Chile have discovered a potential new dwarf planet, designated 2026 ED138, lurking billions of kilometers beyond Pluto less than five months into the telescope’s decade-long survey.
In Plain English: The Clinical Takeaway
- What was found: A massive icy body in the outer solar system, roughly 47 times farther from Earth than Earth is from the sun, measuring between 600 and 1,500 kilometers wide.
- How it was missed: The object moves slowly, completing one solar orbit every 280 years, and was obscured by the dense starfields of the Milky Way.
- What happens next: Astronomers are tracking its orbit to observe a rare occultation—where the object passes in front of a distant star—to determine its exact size, shape, and potential presence of rings or moons.
Mapping the Fringes of the Solar System
The outer solar system is yielding its secrets to the Vera C. Rubin Observatory, perched high on a mountain in Chile. Astronomers revealed at a gathering of the American Astronomical Society’s Division of Planetary Sciences held in Spokane, Washington, as noted by sciencenews.org, that a prospective new dwarf planet had already surfaced in the telemetry less than five months into the facility’s 10-year sky mapping initiative. Another team reported a handful of new Neptune Trojans—icy objects sharing an orbit with Neptune—at the meeting and in the Astrophysical Journal Letters. These findings are filling in astronomers’ picture of the Kuiper Belt at the solar system’s frigid fringes.
“It feels a little bit like we’re replicating the 1800s and early 1900s, discovering what the solar system even looks like in general,” says Sam Deen, an amateur astronomer based in Simi Valley, California, as reported by sciencenews.org. “We’re finding out what there even is in the first place that makes up most of the Kuiper Belt.”
Recovering a Hidden World from Historical Archives
The Vera C. Rubin Observatory is mapping the entire southern sky every couple of nights, searching for faint and fast-moving cosmic objects. The observatory took its first images in June 2025 and officially began its decade-long survey in June 2026. Prior to the commencement of the official monitoring program, Rubin had already registered the displacement of a body traversing the void several billion kilometers past Pluto.
Rubin observed the object 30 times on 20 nights from March 4 to July 11, 2026. However, its presence went unnoticed until October 13, when astrophysicist Matt Holman of the Smithsonian Astronomical Observatory in Cambridge, Massachusetts, ran a search for moving dots of light in the data. Distance calculations placed the body, cataloged as 2026 ED138, at roughly 47 astronomical units from Earth, meaning it was situated about 47 times farther away than our planet is from the sun. Its brightness suggests a diameter between 600 and 1,500 kilometers, placing it in a size category comparable to known dwarf planets like Ceres and Makemake (NASA Dwarf Planets Overview). This scale is likely sufficient for gravity to have pulled it into a spherical shape.
“It’s really big. “No matter what you call it, it’s still the biggest thing we’ve found in the entire solar system in 19 years.”
When Holman realized what he had found, he was thrilled but cautious. “It’s quite an exciting thing,” Holman said in a news briefing at the meeting on October 27, as reported by sciencenews.org. “But one of the things that you need to do when you discover something potentially of this size is to try to verify that it’s true.”
Holman and his colleagues verified the object by locating it in archived data from the Dark Energy Camera, located on an adjacent mountaintop in Chile, from 2016. Amateur astronomers traced it back even further, finding it on photographic plates taken during a sky survey at Palomar Observatory in California in 1954. “They took an image from Palomar in 1954, and another about half an hour after the first one, that both by pure chance happen to point at where ED138 is,” Deen says. “And it’s really obvious. If you know it’s supposed to be there, it’s not particularly faint.”
Observational Challenges and Upcoming Occultations
The object evaded earlier detection because it crawls across the sky, completing an orbit around the sun once every 280 years. It also traveled against a dense backdrop of Milky Way stars, where it blended in seamlessly.
By combining observations spanning decades, astronomers calculated the object’s orbit with increased precision. Deen aims to observe the potential new dwarf planet pass in front of a distant star. Such an event, known as an occultation, can reveal critical details regarding the object’s size, shape, and whether it possesses moons or rings. Ordinarily, determining an object’s orbit with sufficient precision to predict an occultation requires years of study. “Getting to do it immediately is like being a kid in a candy shop, really,” Deen notes.
| Object Designation | Estimated Size Range | Orbital Characteristics | Discovery Context |
|---|---|---|---|
| 2026 ED138 | 600 – 1,500 km | ~280-year solar orbit; Kuiper Belt | Vera C. Rubin Observatory data, verified back to 1954 Palomar plates |
| Neptune Trojans (New Cluster) | Undeclared exact diameters | Trailing Neptune’s orbit at 60 degrees | Discovered in Rubin commissioning phase data masked by Milky Way |
Tracing Solar System Origins via Neptune Trojans
Alongside the dwarf planet candidate, a crop of newly spotted Neptune Trojans was also identified. These asteroids gather in the same orbit as Neptune, offset from the planet by 60 degrees. Astronomers hypothesize that these objects represent primordial building blocks of the solar system, preserving an ancient record of planetary formation and evolution.
"We would expect these groups to be symmetric in numbers, so you have to get more than two," planetary scientist Meg Schwamb of Queen's University Belfast stated in a news conference at the meeting on October 28, according to sciencenews.org. The trailing cloud had remained positioned in front of the Milky Way from Earth's perspective for 15 years, making individual detections difficult. Schwamb and her colleagues examined Vera Rubin data from the telescope's commissioning phase, finding two more trailing Trojans and one candidate.
“This is really the appetizer for what Rubin Observatory is going to do in its mission for the next ten years,” Schwamb added, as noted by sciencenews.org. “There’s hundreds more of these objects likely to be found.”
Future Satellite Interference and Outlook
“There are one hundred new satellites launching every week, and they keep getting bigger and brighter. These discoveries will be hindered by that.”
“Just finding a dwarf planet so quickly, maybe we’ll find something even bigger,” Lawler says. “There could be something the size of Mars out there. And then we’d have the whole planet debate all over again. It would be fun.”
References
- American Astronomical Society – Division of Planetary Sciences Meeting Proceedings (Spokane, Wash., October 2026).
- Astrophysical Journal Letters – Research reports on Neptune Trojan discoveries.
- NASA Science – Dwarf Planets Overview and Classification Guidelines.
