Astronomers announced on 27 October 2026 that 2026 ED138, a body beyond Neptune, is a candidate dwarf planet.
The team said the object was discovered by Matthew Holman, a member of the Center for Astrophysics | Harvard & Smithsonian.
Scientists say 2026 ED138 is likely between 600 and 1,500 kilometres (373 to 972 miles) wide. It currently lies about 46 astronomical units (AU) from the sun, beyond Pluto's average distance of roughly 40 AU.
On 13 October 2026, Holman found the object by searching earlier Rubin observations with code he developed alongside his CfA colleague Kevin Napier. The data showed 2026 ED138 in 30 observations across 20 nights from 4 March to 11 July 2026.
My first reaction was one of excited disbelief
Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.
The Dark Energy Camera (DEC) at Chile's Cerro Tololo Inter-American Observatory has observations of 2026 ED138 dating back to 2016. Mounted on the Víctor M. Blanco 4-meter Telescope, it also captured the object in 2017, 2018, 2019 and 2023.
In June of this year, Rubin Observatory began its 10-year Legacy Survey of Space and Time (LSST). Every few days, Rubin photographs the entire southern sky with a 3.2-gigapixel astronomy camera, the biggest digital camera ever built for the field.
Scientists say a gravitational encounter with Neptune likely altered 2026 ED138's course. Its orbit now sits at an angle of about 25 degrees to the solar system's plane.
Astronomers have confirmed just five dwarf planets to date: Pluto, Ceres, Eris, Haumea and Makemake.
If confirmed as a dwarf planet, ED138 would join a very small family of worlds
Because it lay in a crowded section of the Milky Way, packed with stars, the object was difficult to distinguish, the discovery team said.
Astronomers can estimate 2026 ED138's diameter from its brightness and distance, though surface reflectivity complicates the calculation. An icy, reflective small body may shine as brightly as a much bigger, darker one. More observations, especially in infrared wavelengths, will help determine the object's dimensions and whether it qualifies as a dwarf planet. NASA's James Webb Space Telescope is designed to detect infrared light, the wavelengths needed to establish 2026 ED138's size.
Rubin Solar System Lead Scientist Mario Jurić of the University of Washington contributed to the finding that Rubin had detected 2026 ED138.
This is hopefully just the first of many finds
In 2006, the International Astronomical Union reclassified Pluto, removing it from the planet category and creating a new one: dwarf planet. A dwarf planet is round, but lacks enough mass to dominate gravitationally in its orbital neighborhood.
Beyond the Kuiper Belt, a broad zone of icy bodies reaching about 55 astronomical units, lies the proposed Oort Cloud, potentially stretching tens of thousands of astronomical units into space. Thousands of trans-Neptunian objects have been found, including dwarf planets and smaller icy bodies. Comets heading toward the inner Solar System also reveal material from more remote areas. Far from the Sun, these objects get little light to reflect, so they’re exceptionally dim in optical wavelengths, and their thermal emission in the far infrared is weak. Many travel around the Sun on sharply tilted paths, leaving astronomers with a much larger area of sky to inspect.
Rubin has discovered over 11,000 asteroids that were previously unknown. Its 3.2-gigapixel camera captures a patch of sky about the size of 40 full moons in one exposure. The survey, which began in June 2026 and runs for a decade, is expected to turn up thousands of new objects in the outer Solar System.
The finding neither confirms nor rules out Planet Nine, a proposed object between Earth and Neptune in size that some astronomers think may exist in the distant solar system. A still-undetected massive world called Planet Nine is one explanation for the unusual paths of certain far-off trans-Neptunian objects. Rubin may reveal whether those odd orbits are caused by a distant planet or by rocks arranged in a planet-like shape.
there could easily be a Mars-sized object out there that just hasn't been found yet, or bigger
Rubin will image the whole southern sky again and again for 10 years, so any others hiding in the places earlier surveys skipped are now within reach.
But it is evidence that we have the capacity to find things and that there are amazing things left to be found
Further observations, particularly at infrared wavelengths, are needed to pin down 2026 ED138's size and whether it meets the criteria for dwarf planet status, astronomers say.
