Icy object beyond Pluto emerges as dwarf planet candidate
Known as 2026 ED138, the object has an estimated diameter of 600 to 1,500 km, but further observations are needed to establish its size.
Astronomers working with Chile’s Vera C. Rubin Observatory have announced an icy object beyond Pluto that could qualify as the solar system’s sixth officially recognized dwarf planet. Provisionally named 2026 ED138, it is about 46 astronomical units from the Sun.
Its diameter remains uncertain. Astronomers estimated a range of 600 to 1,500 km using its apparent brightness, distance and assumptions about how much light its surface reflects. Mario Jurić, Rubin’s solar system lead, estimated it at roughly 1,000 km.
The object appears against the densely populated star field near the Milky Way’s plane, making detection difficult. Rubin repeatedly photographs the southern sky, allowing astronomers to identify objects that move between observations.
On October 13, Harvard & Smithsonian astrophysicist Matthew Holman identified ED138 while processing Rubin observations with software developed alongside Kevin Napier. Jurić subsequently found it in 30 images taken over 20 nights from March through July. Earlier surveys also recorded it, extending the observation record to 2016.
Dwarf planet status requires sufficient mass for gravity to make an object round. Infrared observations are needed to establish ED138’s actual size. Official recognition could take longer: the International Astronomical Union has not added Quaoar or Gonggong to its list, although research papers often classify both as dwarf planets.
