Rubin Observatory finds possible sixth dwarf planet beyond Pluto

A large object beyond Pluto has been discovered by the NSF–DOE Vera C. Rubin Observatory, and the IAU Minor Planet Center assigned it the provisional designation 2026 ED138 on Oct. 27, 2026.

ED138 is about 46 astronomical units away, beyond Pluto’s average distance of 40 astronomical units, making it a trans-Neptunian object (an object orbiting beyond Neptune). Its path tilts almost 25 degrees from the solar system’s plane, and researchers say Neptune’s gravity disturbed it from its original path. Matthew Holman and Mario Jurić presented the discovery on Oct. 27, 2026, at the 58th Annual Division for Planetary Sciences meeting in Spokane, Washington.

Researchers estimate the object measures between 600 and 1,500 kilometers across, based on its distance, brightness, and estimated surface reflectivity. Researchers expect bodies of that scale to be round, a requirement for dwarf planet status, though not every trans-Neptunian object is massive enough for its own gravity to pull it into a sphere. Researchers still need infrared observations to pin down the exact dimensions and confirm the object’s nature.

Matthew Holman, who works at the Center for Astrophysics | Harvard & Smithsonian, uncovered the object on October 13, 2026, by running Rubin data through software he built with Kevin Napier to spot repeat detections of the same moving body. Holman said his first reaction was excited disbelief, and he immediately checked whether he or the code had made an error because such objects are very rare. He develops algorithms to find distant moving objects.

Rubin logged 30 detections of the object across 20 nights from March 4, 2026, to July 11, 2026. Archival images from the Dark Energy Camera, located through the Asteroid Institute’s ADAM Precovery service, extend the record back to 2016. The NSF Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory hosts the camera, part of NSF NOIRLab.

Millions of stars crowd the sky region near the Milky Way‘s plane, and they probably hid the object. Rubin’s regular southern-sky monitoring and sorting algorithms spotted the object’s motion. Most telescopes would have lost it among background sources. Rubin can also search older images for the object even when no one knew to look there, speeding up orbit determination.

Confirmation would make the object a sixth dwarf planet, joining the five worlds the International Astronomical Union already recognizes: Pluto, Ceres, Eris, Haumea, and Makemake. Early analysis places it among the biggest dwarf planet candidates beyond Neptune. Researchers using other observatories can now conduct follow-up observations to learn more about its characteristics.

Researchers still need infrared measurements to fix the object’s exact dimensions and confirm dwarf-planet status. The orbital record spans more than 10 years. The International Astronomical Union Minor Planet Center revealed the discovery through a Minor Planet Electronic Circular on Oct. 27, 2026.

Mario Jurić, a University of Washington astronomy professor and Rubin’s solar system lead scientist, said the object is the largest trans-Neptunian object discovered in roughly 20 years, during commissioning. “Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation,” Jurić said. He added that finding objects in older images is changing how quickly and accurately researchers determine distant solar system orbits.

Jurić said Rubin can survey the sky using speed, depth, and precision, and that finding objects this way changes how researchers determine orbits. Holman said confirmation as a dwarf planet would place the object in a small family of worlds. He also said Rubin will repeatedly image the whole southern sky for 10 years, which puts other hidden objects within reach.

The observatory sits on Cerro Pachón in Chile, with joint funding from the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science. The LSST Camera carries 3200 megapixels and ranks as the largest digital camera ever built. At night, Rubin captures a fresh sky image every 40 seconds, and the system issues public alerts within two minutes of spotting a change.

On Feb. 24, 2026, the observatory sent out 800,000 alerts in a single night, and the alert system could reach seven million per night during the 10-year survey. The survey will scan the southern sky each night using the largest digital camera ever constructed. Newswise projects that during LSST’s first year, Rubin will photograph more celestial bodies than every other optical observatory in history combined.

Information moves from Chile to SLAC’s data center in California for early processing, and the system matches it against templates built from prior images of the same patch of sky. The public can explore the object on Orbitviewer, an interactive web app that displays solar system objects in three dimensions and real time. Scientists with data rights can access images through the Rubin Science Platform.

The observatory started gathering early Legacy Survey of Space and Time data in June 2026. In April, it sent more than 11,000 new asteroid observations, including about 380 trans-Neptunian objects, to the Minor Planet Center. Researchers called that April submission a first installment.

Researchers examine trans-Neptunian objects to understand how the solar system formed, how giant planets moved, and how giant planets scattered smaller bodies. Not every trans-Neptunian object qualifies as a dwarf planet candidate. The difference depends on whether an object’s gravity is strong enough to pull it into a round shape.

Edward Ajhar, the NSF program director for Rubin Observatory, said the facility captures movement and change among many never-before-seen objects, revealing details about the solar system, the Milky Way, and billions of galaxies. Kathy Turner, the Department of Energy program manager for Rubin Observatory, said the facility’s unique capabilities make it a powerful instrument for studying astrophysical topics including dark energy and this newly identified dwarf planet candidate.

The facility takes its name from Vera Rubin, who supplied the first convincing proof that dark matter exists. It runs the largest camera ever constructed, and NSF NOIRLab and SLAC National Accelerator Laboratory operate it together.