NSF and DOE’s Rubin Observatory finds a dwarf planet candidate

Beyond the orbit of Pluto, the NSF-DOE Vera C. Rubin Observatory has identified 2026 ED138, a newly discovered object and dwarf planet candidate. Matthew Holman of Astrophysics | Harvard & Smithsonian found the candidate while refining Rubin’s algorithms for detecting distant moving objects, demonstrating the observatory’s capabilities even during testing phases. Initial analysis suggests 2026 ED138 may be among the largest and brightest bodies discovered in the trans-Neptunian region, and Holman recalls his initial reaction was “one of excited disbelief.”

Rubin Observatory Discovers Trans-Neptunian Object 2026 ED138

The newly identified trans-Neptunian object 2026 ED138 currently resides approximately 46 astronomical units from the Sun, placing it slightly beyond the average orbital distance of Pluto at 40 au. This distance firmly categorizes the object as a trans-Neptunian object, orbiting the Sun at a greater distance than Neptune.

Initial observations suggest 2026 ED138 may rank among the largest and brightest objects discovered in this remote region of the Solar System, prompting further investigation into its composition and characteristics. “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,” Holman explained.

This capability is transforming how quickly and accurately orbits can be determined and the distant Solar System understood. Rubin Observatory’s unique strengths extend beyond simply identifying new objects. It is capable of capturing movement and change among a vast number of phenomena previously unseen. This power greatly extends the capacity to reveal and understand new things about the Solar System, the Milky Way and billions of other galaxies across the Universe.

Rubin Observatory is jointly funded by the U.S. National Science Foundation and the U.S. Office of Science. “Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision,” the observatory team reports. With the largest camera ever built, Rubin Observatory is expected to create an ultra-wide, ultra-high-definition, time-lapse record of the Universe, promising a wealth of new discoveries in the years to come.

Holman’s Search Code Uncovers Bright Dwarf Planet Candidate

This unexpected finding highlights the observatory’s capacity to yield discoveries even during its testing phases, demonstrating the effectiveness of the search code developed with colleague Kevin Napier. The code functions by comparing billions of detections, identifying those that correspond to the same object, and ultimately revealing previously unseen celestial bodies. Initial observations indicated an unusually large object, prompting Holman to meticulously verify the results. “My first reaction was one of excited disbelief,” Holman said, explaining his immediate need to rule out any errors in the data or the code itself.

A detailed search through the collected data followed, seeking further observations of ED138 to confirm its existence and orbital characteristics. Mario Jurić, faculty at the University of Washington and Rubin Solar System Lead Scientist presented these results alongside Holman at the 58th Annual Division for Planetary Sciences meeting in Spokane, Washington. If confirmed by the International Astronomical Union Minor Planet Center, ED138 would be among the largest dwarf planets ever discovered in this region of the Solar System.

ED138’s Orbit Reveals Hot-Classical Trans-Neptunian Status

Analysis of 2026 ED138’s orbital path confirms its classification as a hot-classical trans-Neptunian object, a designation stemming from its 25-degree tilt relative to the plane of the Solar System and suggesting past gravitational interactions with Neptune. This orbital characteristic distinguishes ED138 from other trans-Neptunian objects and provides clues to its formation and evolutionary history within the outer Solar System.

The team determined this tilt by combining observations spanning over a decade, using both Rubin Observatory data and archival images from the Dark Energy Camera mounted on the NSF Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory. This distance, coupled with initial size estimates, prompted further investigation into whether the object meets the criteria for dwarf planet status, requiring sufficient mass for self-gravitation into a rounded shape.

Combined Data from Rubin and DECam Track 10-Year Orbit

Combining observations from the Rubin Observatory’s Simonyi Survey Telescope and the Dark Energy Camera on the Blanco 4-meter Telescope, astronomers have reconstructed a decade-long orbital path for the dwarf planet candidate 2026 ED138, revealing details impossible with shorter observation windows. This process demonstrates the observatory’s capacity to use existing astronomical resources, maximizing the scientific return from both current and past observations. The extended timeline provided by the combined data is important for accurately determining ED138’s orbital parameters, including its inclination and eccentricity, which provide clues to its origin and evolutionary history.

Rubin Observatory’s Capabilities Enable Solar System Discovery

The team submitted observations of over 11,000 new asteroids, including roughly 380 trans-Neptunian objects, to the IAU Minor Planet Center in April, anticipating further discoveries as the main survey commenced. Kathy Turner, DOE’s Program Manager for Rubin Observatory, emphasized the observatory’s unique strengths extend beyond dark energy research to encompass the identification of this dwarf planet candidate.

The discovery of 2026 ED138 validates early predictions made by the Rubin Solar System team, who previously characterized their large submission of observations as “the tip of the iceberg.” The team’s confidence stemmed from the observatory’s design, intended to reveal a far greater number of objects than previously possible with existing telescopes. This early success suggests a substantial increase in the rate of trans-Neptunian object discoveries is now underway. The observatory’s power lies in its capacity to capture faint changes in position over time, a critical feature for identifying distant, slowly moving objects.

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