Researchers at the Vera C. Rubin Observatory in Chile have identified a distant body, provisionally designated 2026 ED138, that may join the ranks of known dwarf planets. The object lies roughly 46 astronomical units (AU) from the Sun—just beyond Pluto’s average orbit of 40 AU—and belongs to the population of trans‑Neptunian objects (TNOs) that populate the outer solar system.
Size and Brightness
Initial estimates place the diameter of 2026 ED138 between 600 and 1,500 kilometers, making it one of the larger and brighter TNOs observed to date. Its apparent brightness, combined with its distance, suggests the object could be among the most easily detectable members of this distant class.
Discovery and Observation History
The object was first flagged on October 13 by Matthew Holman, a researcher at the Harvard‑Smithsonian Center for Astrophysics and part of the Rubin Observatory’s operations team. Holman identified the source while reviewing data collected by the telescope in 2026. Subsequent analysis uncovered additional images of the same object in archived observations dating back to 2016, allowing the team to piece together more than a decade of its orbital path.
ED138 managed to evade earlier detection because it appears against the bright backdrop of the Milky Way’s disk, a region dense with stars that can obscure fainter objects. The Rubin Observatory’s massive data processing capabilities enabled astronomers to isolate the faint signature of the object amid this stellar crowd.
Classification Challenges
While the object meets basic criteria for dwarf‑planet status—orbiting the Sun and possessing sufficient mass to assume a near‑spherical shape—its classification remains pending. Determining whether its gravity has indeed shaped it into a sphere requires more precise measurements of its size and mass, which are difficult to obtain at such distances.
If confirmed, 2026 ED138 would become the sixth dwarf planet recognized by the International Astronomical Union, joining Ceres, Pluto, Haumea, Makemake, and Eris. It would also add to a growing list of candidates that include Gonggong, Quaoar, Sedna and Orcus, among dozens of other outer‑solar‑system bodies that exhibit dwarf‑planet characteristics.
Confirming dwarf‑planet status for distant objects is a complex task. Direct imaging of Pluto, for example, required the New Horizons probe, which traveled nearly nine and a half years from launch in 2006 to its 2015 flyby. Even farther objects, such as the small planetesimal Arrokoth, demanded similarly lengthy missions.
Context Within the Solar System
The solar system extends far beyond the eight planets commonly depicted in textbooks. In addition to planets and moons, it contains a myriad of small bodies, including dwarf planets, asteroids, comets and countless TNOs. The Kuiper Belt stretches out to about 50 AU, while the scattered disk reaches nearly 1,000 AU. Beyond these regions lies the Oort Cloud, a hypothesized shell that may extend up to 100,000 AU, though it has never been directly observed.
As surveys like those conducted by the Rubin Observatory continue to scan the sky, astronomers expect to uncover more distant objects that could reshape our understanding of the solar system’s outer frontier.
Steve Lopez is a Senior Editorial Columnist and Health & Public Policy reporter for News Raise. Steve focuses on healthcare advancements, medical technologies, and public health policies.
