Astronomers using the NSF-DOE Vera C. Rubin Observatory have identified what could be a new dwarf planet beyond Neptune. The object, provisionally designated 2026 ED138, appears to be a large icy body between 600 and 1,500 kilometers (373 to 932 miles) across, although infrared observations will be needed to determine its precise size and confirm its status.
Mosaic of images taken by the Vera Rubin Observatory in 2026 ED138. Image credits: NSF / DOE / Vera C. Rubin Observatory / NOIRLab / SLAC / AURA / M. Jurić, University of Washington / D. de Martin & M. Zamani, NSF’s NOIRLab.
A possible new dwarf planet
“Rubin gives us an unprecedented ability to explore the sky with a combination of speed, depth, and precision,” said Dr. Mario Juric, Rubin Solar System Principal Scientist at the University of Washington.
“And this discovery is just the beginning. Once we identify a new object, we can search back months or even decades to find it in images no one knew to see.”
“This ability to discover and ‘pre-spot’ objects is transforming how quickly and accurately we can determine the trajectory of objects and understand our distant solar systems.”
Juric and his colleagues estimate ED138’s diameter from its brightness, distance and assumed reflectance. An icy object of this size would be expected to become round under its own gravity, which is one of the requirements for classification as a dwarf planet.
Infrared observations will be required to establish the object’s exact dimensions. If its status is confirmed, ED138 would become the sixth dwarf planet to be identified, joining Pluto, Ceres, Eris, Haumea and Makemake.
“The superpower of Rubin Observatory is its ability to clearly see motion and change among a vast number of objects and phenomena never seen before by humans,” said Dr. Edward Ajar, NSF program director at Rubin Observatory.
“Its power greatly expands our ability to reveal and understand new things about our solar system, the Milky Way, and the billions of other galaxies in the universe.”
“The unique strengths of Rubin Observatory make it an excellent tool for investigating a wide range of astrophysical phenomena, from dark energy to the discovery of this dwarf planet candidate,” added Dr. Kathy Turner, DOE’s Rubin Observatory program manager.
An object in the Kuiper belt
ED138 is currently about 46 astronomical units (AU) from the Sun. One AU is the average distance between Earth and the Sun; Pluto’s average distance is about 40 AU.
The object is therefore a trans-Neptunian object, a class of icy bodies that orbit beyond Neptune. Its orbit is tilted by approximately 25 degrees relative to the plane of the solar system, making ED138 a “hot classic” Kuiper belt object. These objects are thought to have been displaced from their original orbits by Neptune’s gravity.
Despite its size, ED138 went unnoticed because it lies in a region of the sky near the Milky Way’s dense stellar surface, where millions of stars can make faint objects difficult to detect.
Repeated surveys reveal faint motion
The discovery was enabled by Rubin Observatory’s software, which repeatedly scans the southern sky for the faint movements of distant objects.
“If confirmed as a dwarf planet, ED138 would join a group of very small worlds,” said Dr. Matthew Holman, an astronomer at Harvard University and the Smithsonian Center for Astrophysics.
“Rubin will photograph the entire southern sky repeatedly over a 10-year period, so others hiding in places where previous surveys skipped are now within reach.”
M. Juric et al., “2026 ED138,” MPEC 2026-U85.
Source: www.sci.news
