NSF–DOE Vera C. Rubin Observatory reveals its first dwarf planet candidate in our solar system

Read this release on the Vera C. Rubin Observatory website

In the outer reaches of our solar system, beyond the orbit of Pluto, NSF–DOE Vera C. Rubin Observatory has spotted 2026 ED138 — a large, bright trans-Neptunian object that scientists have identified as a dwarf planet candidate. The observations were announced today by the International Astronomical Union Minor Planet Center (MPC). If confirmed, ED138 would be among the largest dwarf planets ever discovered in this region of the solar system.

With observations taken during the run up to the Legacy Survey of Space and Time (LSST), NSF–DOE Vera C. Rubin Observatory has discovered a new dwarf planet candidate in our solar system. The candidate, which has been given the provisional designation 2026 ED138 (ED138), was found by Rubin Operations team member and in-kind contributor Matthew Holman (Center for Astrophysics | Harvard & Smithsonian [CfA]). He contributes to improving Rubin's algorithms that search for distant moving objects in our solar system. The candidate’s distance from the sun places it beyond the orbit of dwarf planet Pluto. Initial analysis indicates that it may be among the largest and brightest bodies scientists have discovered in this region of the solar system.

Rubin Observatory is jointly funded by the U.S. National Science Foundation and the U.S. Department of Energy's Office of Science.

“Rubin Observatory's superpower is the ability to clearly capture movement and change among a vast number of objects and phenomena that humans have never seen before,” said Edward Ajhar, NSF Program Director for Rubin Observatory. “That power greatly extends our ability to reveal and understand new things about our solar system, the Milky Way, and billions of other galaxies across the universe.”

“Rubin Observatory’s unique strengths make it an incredible tool for investigating a wide range of astrophysical phenomena, from dark energy to the discovery of this dwarf planet candidate,” said Kathy Turner, DOE’s Program Manager for Rubin Observatory.

Today, MPC announced the discovery in a Minor Planet Electronic Circular. Mario Jurić, faculty at the University of Washington and Rubin solar system Lead Scientist, and Holman presented the results at a press conference at the 58th Annual Division for Planetary Sciences (DPS) meeting in Spokane, Washington.

On the evening of 13 October, Holman was running data collected by Rubin earlier in 2026 through a search code he developed with CfA colleague Kevin Napier. The code is built to look at billions of detections of moving objects, compare them, and find the detections that correspond to the same object. Using this method, Holman uncovered ED138, and he immediately noticed that its brightness and distance indicated that it is unusually large.

“My first reaction was one of excited disbelief,” Holman said. “Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.”

To remove any doubt, a detailed search through the data began in the hopes of uncovering more observations of ED138. Jurić searched Rubin’s catalogs and images and found 20 more observations, going back to 4 March 2026. In all, Rubin observed ED138 30 times on 20 nights between 4 March and 11 July. Additional archival images from the DOE-fabricated Dark Energy Camera (DECam), and uncovered by the Asteroid Institute’s ADAM Precovery service, provided data going all the way back to 2016. These data allowed the team to trace more than 10 years of ED138's orbit. DECam is mounted on the NSF Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF NOIRLab.

ED138 is currently at a distance of about 46 astronomical units (au), where 1 au is the average distance between the Earth and the sun. For reference, dwarf planet Pluto has an average distance of 40 au. This classifies ED138 as a trans-Neptunian object (TNO) — objects that orbit the sun at a distance greater than Neptune’s.

Scientists study the size, composition, and orbital trajectories of TNOs to understand how the solar system formed, how the giant planets migrated over time, and how smaller objects have been scattered throughout this evolution. ED138’s orbit is tilted almost 25 degrees off of the plane of the solar system, classifying it as a hot-classical TNO and suggesting that it was disturbed from its original orbit through gravitational interactions with Neptune.

Not all TNOs are considered dwarf planet candidates, with the distinction being in the size and shape of the object. To be a dwarf planet an object needs to be massive enough for its own gravity to pull it into a round shape. Based on ED138’s distance, brightness and estimated surface reflectivity (albedo), the team estimates that its size is between 600 and 1500 kilometers, and icy bodies this large are expected to be round.

This preliminary analysis places ED138 among the largest dwarf planet candidates ever discovered beyond Neptune, though observations in the infrared are needed to constrain its exact size and confirm its nature as a dwarf planet. If confirmed, ED138 would join the five dwarf planets recognized by the International Astronomical Union (IAU): Pluto, Ceres, Eris, Haumea, and Makemake.

ED138 was found in a region of sky close to the plane of the Milky Way — a crowded region filled with millions of stars. To most telescopes, ED138 has been lost among the myriad background sources, which is likely why it was not discovered until now. Rubin Observatory’s regular and continuous monitoring of the entire Southern Hemisphere sky, combined with powerful algorithms that sift through millions to billions of points of light to identify those corresponding to small moving objects, enabled the team to spot ED138 within the crowded field.

“Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision,” Jurić said. “And the discovery is just the beginning: once we identify a new object, we can search back months, and sometimes even decades, finding it in images where nobody knew to look. This ability to both discover and ‘precover’ objects is transforming how quickly and accurately we can determine their orbits and understand the distant solar system.”

ED138 joins the rapidly growing sample of solar system objects discovered by Rubin since it began collecting early data in preparation for the LSST, which began in June 2026. In April, before LSST formally began, the Rubin Solar System team submitted observations of over 11,000 new asteroids to the IAU Minor Planet Center (MPC), which included roughly 380 new TNOs. At the time, the team called this large submission “the tip of the iceberg” and expressed their excitement for the discoveries to come once LSST began. With the discovery of ED138, those hopes are coming to fruition.

“If confirmed as a dwarf planet, ED138 would join a very small family of worlds,” Holman said. “Rubin will image the whole southern sky again and again for ten years, so any others hiding in the places earlier surveys skipped are now within reach.”

Now that Rubin has identified ED138, scientists around the globe can organize follow-up observations to uncover even more information about its nature. Images of ED138 are made available to Rubin data rights holders on the Rubin Science Platform, an online, web-based environment where scientists can access, explore, and process the massive amounts of data being produced by the LSST. The public can also interact with this discovery on Orbitviewer, an interactive web-based app that provides an intuitive way to explore the structure of our cosmic backyard in three dimensions and in real time.

More information

The Rubin Solar System Operations team is composed of Mario Jurić, Aren Heinze, Jacob A. Kurlander, Matthew J. Holman, Kevin J. Napier, Ian Sullivan, Eric C. Bellm, Megan E. Schwamb; Joachim Moeyens, Ian Chow, Pedro H. Bernardinelli, Colin Orion Chandler, Sarah Greenstreet, Samuel Cornwall, Siegfried Eggl, Chester Li, Eric J. Christensen, Erfan Nourbakhsh, James E. Robinson, Devanshi Singh, and Danica Zilkova.

NSF–DOE Vera C. Rubin Observatory, funded by the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science, is a groundbreaking new astronomy and astrophysics observatory on Cerro Pachón in Chile. It is named after astronomer Vera Rubin, who provided the first convincing evidence for the existence of dark matter. Using the largest camera ever built, Rubin is repeatedly scanning the sky for 10 years to create an ultra-wide, ultra-high-definition, time-lapse record of our universe.

NSF–DOE Vera C. Rubin Observatory is a joint initiative of the U.S. National Science Foundation (NSF) and the U.S. Department of Energy’s Office of Science (DOE/SC). Its primary mission is to carry out the Legacy Survey of Space and Time, providing an unprecedented data set for scientific research supported by both agencies. Rubin is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory. NSF NOIRLab is managed by the Association of Universities for Research in Astronomy (AURA) and SLAC is operated by Stanford University for the DOE. France provides key support to the construction and operations of Rubin Observatory through contributions from CNRS/IN2P3. Rubin Observatory is privileged to conduct research in Chile and gratefully acknowledges additional contributions from more than 40 international organizations and teams.

The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

The DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. 

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

SLAC National Accelerator Laboratory explores how the universe works at the biggest, smallest, and fastest scales and invents powerful tools used by researchers around the globe. As world leaders in ultrafast science and bold explorers of the physics of the universe, we forge new ground in understanding our origins and building a healthier and more sustainable future. Our discovery and innovation help develop new materials and chemical processes and open unprecedented views of the cosmos and life’s most delicate machinery. Building on more than 60 years of visionary research, we help shape the future by advancing areas such as quantum technology, scientific computing, and the development of next-generation accelerators. SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science.