TESS Archive Adds Seven Years of Observations for Dwarf-Planet Candidate 2026 ED138

![TESS observations of 2026 ED138 stacked along its predicted path; the combined detection is at right](https://arxiv.org/html/2610.40106v1/ed138_tess_orbit.png) Figure: Te Han et al., arXiv:2610.40106, CC BY 4.0. A telescope built to find planets around distant stars also captured a faint object far beyond Neptune—years before astronomers knew to look for it. In a preprint posted October 29, MIT researchers report finding the dwarf-planet candidate 2026 ED138 in five month-long sectors of NASA’s TESS archive, spanning 2019 to 2026. Four of those observing periods predate the candidate’s October 27 announcement by the Vera C. Rubin Observatory. TESS did not discover the object. Rubin first identified it in its 2026 survey data; earlier images from the Dark Energy Camera also helped extend its record back to 2016. The later TESS analysis is an example of “precovery”: once an object’s orbit is known, researchers can search older observations for traces of where it had already been. That search was difficult. ED138 is too faint to pick out in a single TESS frame, and the field is crowded: the team says each 21-arcsecond TESS pixel contains roughly 7 to 21 catalogued stars. They modeled and removed the background stars, suppressed the remaining static light, then shifted and stacked images along ED138’s predicted route. The combined signal reached 34 sigma. The eight TESS positions also agree with the JPL orbit, though they are much less precise than the measurements used to calculate it. The archive has extended the observational timeline, not settled what ED138 is. Its estimated diameter is still broad—about 600 to 1,500 kilometres—and infrared observations are needed to determine whether it is large enough to count as a dwarf planet. The precovery paper is currently an arXiv preprint, so its results have not yet completed peer review. The useful surprise is methodological: old survey images can become new evidence when a later discovery supplies the path to search. TESS’s archive was built for exoplanet work, but it also preserves a record of moving objects crossing its field of view. Read the [TESS precovery paper](https://arxiv.org/abs/2610.40106) and the [Rubin Observatory discovery announcement](https://rubinobservatory.org/news/rubin-first-dwarf-planet-candidate). ~science