Plate Nº 13 · recorded October 30, 2026
Space & AstronomyReported finding
Rubin Observatory Finds Giant Dwarf Planet Candidate in Pluto's Neighborhood
Rubin Observatory's first dwarf planet candidate, 2026 ED138, spans 600-1,500 km and orbits within Pluto's distance range — hiding in plain sight for a decade.
By Elena Vasquez4 min read838 words
In brief
- Object 2026 ED138 measures an estimated 600-1,500 km across and takes about 281 years to orbit the Sun.
- It was first detected in Rubin data on 13 October 2026, traced through 30 detections over 20 nights.
- Archival Dark Energy Camera images show the object as far back as February 2016.
- Rubin's 3.2-gigapixel camera images a sky area about 40 full moons wide per exposure.
- The object's orbit tilts 24.5 degrees and stays between 36.86 and 49.04 AU from the Sun.
A newly discovered object called 2026 ED138, somewhere between 600 and 1,500 kilometers (373 to 932 miles) across, is the first dwarf planet candidate found by the Vera C. Rubin Observatory — and it may have been sitting unnoticed in telescope images for a decade.
The object orbits entirely within Pluto's distance range from the Sun, yet nobody spotted it until now. It may rank among the largest objects ever found in trans-Neptunian space — the region beyond Neptune — potentially rivaling the dwarf planets Makemake and Haumea in size.
"My first reaction was one of excited disbelief," said astrophysicist Matthew Holman of the Harvard-Smithsonian Center for Astrophysics, who made the discovery. "Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong."
He hadn't made a mistake. The code was right.
Why is the space beyond Pluto so hard to see?
The outer Solar System is an anti-Goldilocks zone: too cold and too dark for easy observation. Objects out there get very little sunlight to reflect, so they look extremely faint in visible light. They're also bitterly cold, giving off only a weak thermal glow in the far infrared — light at wavelengths our eyes can't see.
Then there's the motion problem. These bodies drift slowly against the background stars as they circle the Sun, so a telescope must look at the right patch of sky at exactly the right time. Miss it, and the object escapes detection.
Orbital misbehavior compounds the difficulty. Many trans-Neptunian objects orbit at strange angles rather than in the flat plane the inner planets follow, dramatically expanding the sky area astronomers must search.
Scientists have detected thousands of these objects — dwarf planets down to small icy bodies — while comets plunging inward hint at material from even farther out, in the hypothetical Oort Cloud that may stretch tens of thousands of astronomical units into space. An astronomical unit (AU) is the Earth-Sun distance, about 150 million kilometers.
In short: the region beyond 30 AU has been reconstructed from breadcrumbs. Now Rubin is changing that.
How did Rubin catch it?
The observatory, located in Chile, carries the largest digital camera ever built for astronomy: a 3.2-gigapixel instrument that images a patch of sky roughly 40 full moons wide in a single exposure. By repeatedly photographing the same southern-sky regions, it catches faint dots that shift position against the stars — the signature of Solar System objects.
Rubin saw first light in June 2025. By March 2026, ED138 had wandered into view.
On 13 October 2026, Holman was analyzing Rubin data with software built with colleague Kevin Napier when the large, unknown object appeared. The team traced it through 30 detections across 20 nights of observations, spanning 4 March to 11 July 2026.
Then came the archival surprise. Searching older data, the researchers found the Dark Energy Camera had already photographed ED138 in February 2016 — and again in 2017, 2018, 2019, and 2023. For a decade, evidence of this distant world sat waiting in astronomical images.
Those archival detections let the team map its orbit precisely. According to the Minor Planet Center, ED138 takes about 281 years to circle the Sun, swinging between 36.86 AU at its closest approach and 49.04 AU at its farthest. Pluto, for comparison, orbits between 29.6 and 49.08 AU. ED138's average distance, 42.95 AU, sits slightly beyond Pluto's.
Why did it hide for so long?
Two reasons. Its orbit tilts about 24.5 degrees relative to the plane of the Solar System — a textbook case of the orbital shenanigans that hide trans-Neptunian objects from surveys. Worse, it was lurking against the crowded backdrop of the Milky Way, where dense fields of stars camouflaged it further.
Its exact size remains unknown, and there's a catch. Brightness-based estimates can't distinguish a small, highly reflective icy body from a large, dark one. Until infrared measurements pin down how reflective ED138 is, researchers can only give the 600-1,500 km range.
At those dimensions, though, it's likely massive enough for its own gravity to pull it into a roughly spherical shape — a key requirement for dwarf planet status. If confirmed, it will earn a catchier name.
What comes next?
Plenty. Rubin began a decade-long survey in June 2026 and is expected to find thousands of unknown outer Solar System objects, helping astronomers piece together the region's history and evolution.
One tantalizing target is Planet Nine — a hypothetical massive world proposed to explain the odd orbits of some distant objects. Rubin could settle whether those orbits betray a hidden planet or something less dramatic.
"Rubin will image the whole southern sky again and again for ten years," Holman said, "so any others hiding in the places earlier surveys skipped are now within reach."
The takeaway: a giant world hid inside Pluto's orbital neighborhood for years, and Rubin is only getting started.
via rubinobservatory.org (Original)
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Correspondent covering money, funding and market shifts around general science news at SciBeat.
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