Submission + - Rubin Telescope discovers a new solar system planet (behindtheblack.com)
On the evening of 13 October, [Matthew] Holman was running data collected by Rubin earlier in 2026 through a search code he developed with CfA colleague Kevin Napier. The code is built to look at billions of detections of moving objects, compare them, and find the detections that correspond to the same object. Using this method, Holman uncovered ED138, and he immediately noticed that its brightness and distance indicated that it is unusually large. “My first reaction was one of excited disbelief,” says Holman. “Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.”
To remove any doubt, a detailed search through the data began in the hopes of uncovering more observations of ED138. Juri searched Rubin’s catalogs and images and found 20 more observations, going back to 4 March 2026. In all, Rubin observed ED138 30 times on 20 nights between 4 March and 11 July. Additional archival images from the DOE-fabricated Dark Energy Camera (DECam), and uncovered by the Asteroid Institute’s ADAM Precovery service, provided data going all the way back to 2016. These data allowed the team to trace more than 10 years of ED138's orbit. DECam is mounted on the NSF Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF NOIRLab.
ED138 is currently at a distance of about 46 astronomical units (au), where 1 au is the average distance between the Earth and the Sun. For reference, dwarf planet Pluto has an average distance of 40 au. This classifies ED138 as a trans-Neptunian object (TNO) — objects that orbit the Sun at a distance greater than Neptune’s.
The data suggests this new planet is the largest TNO object so far discovered, though at present the size estimate is very uncertain, from 350 to 1400 miles in diameter.
