2026 ED138: Rubin spots a dwarf planet candidate
· BehindLines newsroom
An object detected in data from the Vera C. Rubin Observatory could join the dwarf planet family. Presented on 27 October under the provisional designation 2026 ED138, it remains a candidate: its classification depends in particular on a better measurement of its size.
A discovery in Rubin data
According to the announcement published by SLAC, Matthew Holman identified the object on 13 October by applying search code developed with Kevin Napier to Rubin's 2026 data. The program links detections corresponding to the same moving object. Further searches brought together thirty Rubin observations, taken on twenty nights between 4 March and 11 July 2026.
Images from the DECam camera, located using the Asteroid Institute's ADAM Precovery service, extend the record back to 2016. They therefore provide access to a much longer trajectory than the discovery period alone.
How a retrospective search works
The Asteroid Institute explains that Precovery starts with an orbit and its uncertainty, calculates possible positions on different dates, then searches the archives for corresponding observations. An old image becomes useful once researchers know where to look.
The service states that candidate detections require expert review before any submission to the Minor Planet Center. Finding compatible points and validating their identification remain two separate stages.
A public Rubin technical note also describes the provision of ED138 images and catalogues to data rights holders. The note specifies that measurements submitted to the Minor Planet Center are public, while the rest of the data set remains restricted.
A size that remains uncertain
At the time of the announcement, the object was about 46 astronomical units from the Sun, according to the release. One unit corresponds to the average Earth–Sun distance. Its estimated diameter ranges from 600 to 1,500 kilometres, depending on assumptions about its reflectivity.
Infrared observations are still needed to determine its size more accurately and confirm its nature. The discovery thus supplies a target for astronomical follow-up, without establishing the existence of an officially recognised dwarf planet at this stage.