Scientists may be on the verge of confirming the existence of yet another celestial body within our solar system. Astronomers from the Vera C. Rubin Observatory in Chile have identified an object that could potentially be classified as a dwarf planet, currently located farther from the Sun than Pluto. Provisionally named 2026 ED138, this object is estimated to measure between 600 and 1,500 kilometres in diameter.
Situated approximately 46 astronomical units from the Sun, this object is notably more distant than Pluto, which orbits at an average distance of 40 astronomical units. Due to its location, ED138 is classified as part of the trans-Neptunian object population. The discoverers suggest that it may be one of the brightest known objects of its kind, as well as one of the largest.
Understanding the Classification of Dwarf Planets
The distinction between a planet and a dwarf planet lies in their respective environments. While both orbit the Sun and possess sufficient gravitational force to take on a nearly spherical shape, a planet has cleared its orbit of other bodies of comparable size. In contrast, dwarf planets coexist with other objects in their orbital regions. This fundamental difference is why Pluto was reclassified from a planet to a dwarf planet in 2006.
Matthew Holman, a researcher at the Harvard-Smithsonian Centre for Astrophysics and a member of the observatory’s operational team, first identified ED138 on October 13 while analysing data collected by Rubin during 2026. A more in-depth search revealed additional observations and archival records dating back to 2016. This collection of images enabled the team to reconstruct over a decade of the object’s trajectory.
Astronomers explain that ED138 had managed to “hide” from detection due to its position in a region of the sky near the plane of the Milky Way, where millions of stars make it challenging to discern faint objects. The Vera C. Rubin Observatory’s ability to track celestial movements and analyse vast amounts of data facilitated the identification of ED138 amidst this field of light.
The Journey Towards Confirmation
While ED138’s classification as a dwarf planet remains unconfirmed, astronomers are aware that it is a trans-Neptunian object. They must obtain a more precise measurement of its size to determine if its gravity is sufficient to shape it into a nearly spherical form. If it does not meet this criterion, it will remain categorised as an object in the outer solar system. Further observations will also aid in understanding its physical properties and the nature of this celestial body. Should it fulfil the necessary requirements, ED138 would join the ranks of the five dwarf planets officially recognised by the International Astronomical Union: Ceres, Pluto, Haumea, Makemake, and Eris.
However, ED138 is not the only candidate awaiting classification as a dwarf planet. Astronomers have identified numerous objects in the outer solar system that, based on their size and characteristics, could potentially qualify. Among the most notable contenders are Gonggong, Quaoar, Sedna, and Orcus. Experts acknowledge that the list may be even longer.
The Challenges of Classification
Confirming these bodies as dwarf planets is not a straightforward task. Their immense distances complicate the direct measurement of their size and mass, and particularly, the determination of whether their gravity has shaped them into nearly spherical forms. For instance, obtaining high-resolution images of Pluto necessitated the launch of the New Horizons spacecraft, which took nearly nine and a half years to reach Pluto after its launch in 2006, culminating in a flyby in 2015. Three years later, it reached the even more distant object Arrokoth, a small planetesimal.
The solar system is often depicted as a star surrounded by eight planets, yet it is, in reality, a far more extensive and populated structure. Beyond planets and moons, it includes dwarf planets, asteroids, comets, and a vast array of smaller bodies extending well beyond Neptune. The Kuiper Belt stretches to approximately 50 astronomical units, while the scattered disc reaches nearly 1,000. Much farther out lies the Oort Cloud, a region that has never been directly observed and may extend up to 100,000 astronomical units from the Sun.