Mike Chillit

Astronomers using early data from the Vera C. @VRubinObs Observatory have identified 2026 ED138, a large object beyond Neptune that could qualify as a dwarf planet. It currently lies about 46 astronomical units from the Sun, roughly 6.9 billion kilometres. The discovery was announced on 27 October, although further observations are needed to establish its size and physical properties. Matthew Holman identified the object on 13 October using software developed with Kevin Napier to connect separate detections of moving objects. Mario Jurić then recovered additional observations in Rubin’s data, while searches of other surveys uncovered images dating back to 2016. That archival material gives astronomers more than a decade of observations with which to calculate its orbit. An object can appear in telescope images for years before anyone recognises that those detections belong to the same body. The estimated diameter is between approximately 600 and 1,500 kilometres. This considerable uncertainty comes from its unknown surface reflectivity, or albedo. At a given distance, a smaller object with a reflective surface can appear as bright as a larger object with a darker surface. The often-mentioned diameter of around 1,000 kilometres therefore depends on an assumed albedo. Follow-up measurements could narrow that range, including observations of a stellar occultation, when the object passes in front of a distant star. An icy body of this size could have enough gravity to become approximately rounded, one of the requirements for dwarf planet status. Under the International Astronomical Union’s definition, a dwarf planet orbits the Sun, has sufficient self-gravity to achieve a nearly round shape, has not cleared its orbital neighbourhood and is not a satellite. ED138 remains a candidate while its properties are investigated. ED138 was found against a crowded background of Milky Way stars, which probably helped it escape earlier searches. Rubin’s repeated observations and tracking algorithms allowed researchers to identify its movement through that field. Studying such objects helps reconstruct the early Solar System: their orbits and surface compositions preserve evidence of how the giant planets migrated and redistributed smaller bodies beyond Neptune. 🎃 rubinobservatory.org/es/news…