A Possible Dwarf Planet Was Hiding in Pluto's Neighborhood, and Rubin Just Found It

Astronomers have found a large icy object in the Kuiper Belt that may be a dwarf planet, according to ScienceAlert. Named 2026 ED138, it is the first dwarf planet candidate for the Vera C. Rubin Observatory, and it may be one of the largest objects found so far beyond Neptune.

What makes the discovery striking is where the object lives. Its entire orbit lies within the range of distances at which Pluto circles the Sun, yet it went unnoticed until now.

2026 ED138 by the numbers

• 600 to 1,500 kilometers (373 to 932 miles): the estimated width. The range is wide because brightness alone cannot separate a small, shiny object from a larger, darker one.
• About 281 years: the time the object takes to orbit the Sun once, according to the Minor Planet Center.
• 36.86 and 49.04 astronomical units: its closest and farthest distances from the Sun. Pluto ranges between 29.6 and 49.08 astronomical units.
• About 42.95 astronomical units: its average orbital distance, slightly beyond Pluto's.
• About 24.5 degrees: the tilt of its orbit relative to the plane of the Solar System.
• 30 detections over 20 nights: how often Rubin recorded it, from March 4 to July 11, 2026.

How it stayed hidden

Objects beyond Neptune are hard to spot. They get little sunlight to reflect, so they are extremely faint, and they are so cold that they give off only a weak glow in the far infrared. They also move against the background stars, so a telescope has to look at the right place at the right time.

Orbits add to the problem. Many objects out there travel at odd angles instead of in a flat plane, which widens the area of sky that must be searched. ScienceAlert said 2026 ED138 was also sitting against the crowded backdrop of the Milky Way, where many stars made it harder to pick out.

How Rubin and an old archive found it

Rubin has the largest digital camera ever built for astronomy. Its 3.2-gigapixel camera can image an area of sky equal to around 40 full moons in one exposure, and it returns to the same regions repeatedly so that moving points of light stand out. The telescope saw first light in June 2025, and by March 2026 the object had entered its field of view.

On Oct. 13, 2026, astrophysicist Matthew Holman of the Harvard-Smithsonian Center for Astrophysics was analyzing Rubin observations with software developed with colleague Kevin Napier when the object caught his attention. Holman described his reaction as “excited disbelief” and said he first checked whether he or the code had made a mistake.

The team then searched older data and found the object in images from the Dark Energy Camera, going back to February 2016. The camera also captured it in 2017, 2018, 2019 and 2023. Those older observations extended the record by years and let the researchers work out its orbit.

Why it matters

For most readers, the discovery will not change daily life, but it adds to what is known about the outer Solar System. If the object is at the larger end of the estimate, it could be comparable in size to the dwarf planets Makemake and Haumea. ScienceAlert noted that at those dimensions it is likely massive enough for its own gravity to pull it into a roughly spherical shape, one of the defining traits of a dwarf planet.

The finding also shows what Rubin was built to do. By repeatedly surveying large parts of the southern sky, it can pick out faint, slow-moving objects that earlier surveys missed. The case of 2026 ED138 suggests that such objects can sit in plain sight in old images for years, waiting for someone to look.

The object's exact size is still unknown, and it remains a candidate rather than a confirmed dwarf planet.

Around Prague, based on reporting by ScienceAlert