2026 ED138: A Large Trans-Neptunian Object in Early Rubin Observatory Data, and How Many More May Remain
Abstract
We characterize a large trans-Neptunian object (TNO), 2026 ED138, discovered in data taken by the NSF-DOE Vera C. Rubin Observatory with the linking code pointdexter, and validate it independently. 2026 ED138 has absolute magnitude HV=3.19, implying a diameter of 612-1530 km for geometric albedos between 0.25 and 0.04 and making it one of the ten intrinsically brightest known TNOs and a dwarf-planet candidate. At i≈19.4 it is bright enough in the sky for ground-based spectroscopy and light curves and for detailed study with HST and JWST. Archival DECam detections extend its arc to more than ten years (3789 days). Its orbit, with barycentric a=43.09 au, e=0.139 and i=24.4∘, lies at the edge of the 12:7 mean-motion resonance with Neptune, like that of the dwarf planet Haumea, but with g−r=0.63 it is too red to be a member of Haumea's collisional family. 2026 ED138 was missed by earlier surveys because it lies far south and near the crowded regions of the Galactic plane. Our recoveries of the known TNOs with HV<4 suggest that about 3 more objects like them, and probably more, remain undiscovered away from the Galactic plane. More such objects probably lie within 10∘ of the plane, which no search has yet covered to this depth.
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BibTeX
@misc{holman20262026,
title = {{2026 ED138: A Large Trans-Neptunian Object in Early Rubin Observatory Data, and How Many More May Remain}},
author = {Matthew J. Holman and Mario Jurić and Kevin J. Napier and Jacob A. Kurlander and Aren Heinze and Joachim Moeyens and Megan E. Schwamb and Pedro H. Bernardinelli and Ian Sullivan and Eric C. Bellm and Silvia Protopapa and Colin Orion Chandler and Ian Chow and Eric J. Christensen and Samuel Cornwall and Siegfried Eggl and Sarah Greenstreet and Chester Li and Erfan Nourbakhsh and James E. Robinson and Devanshi Singh and Danica Zilkova},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38693},
eprint = {2610.38693},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38693},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - 2026 ED138: A Large Trans-Neptunian Object in Early Rubin Observatory Data, and How Many More May Remain
AU - Matthew J. Holman
AU - Mario Jurić
AU - Kevin J. Napier
AU - Jacob A. Kurlander
AU - Aren Heinze
AU - Joachim Moeyens
AU - Megan E. Schwamb
AU - Pedro H. Bernardinelli
AU - Ian Sullivan
AU - Eric C. Bellm
AU - Silvia Protopapa
AU - Colin Orion Chandler
AU - Ian Chow
AU - Eric J. Christensen
AU - Samuel Cornwall
AU - Siegfried Eggl
AU - Sarah Greenstreet
AU - Chester Li
AU - Erfan Nourbakhsh
AU - James E. Robinson
AU - Devanshi Singh
AU - Danica Zilkova
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38693
UR - https://arxiv.org/abs/2610.38693
AB - We characterize a large trans-Neptunian object (TNO), 2026 ED138, discovered in data taken by the NSF-DOE Vera C. Rubin Observatory with the linking code pointdexter, and validate it independently. 2026 ED138 has absolute magnitude H_V=3.19, implying a diameter of 612-1530 km for geometric albedos between 0.25 and 0.04 and making it one of the ten intrinsically brightest known TNOs and a dwarf-planet candidate. At i≈19.4 it is bright enough in the sky for ground-based spectroscopy and light curves and for detailed study with HST and JWST. Archival DECam detections extend its arc to more than ten years (3789 days). Its orbit, with barycentric a=43.09 au, e=0.139 and i=24.4^∘, lies at the edge of the 12:7 mean-motion resonance with Neptune, like that of the dwarf planet Haumea, but with g−r=0.63 it is too red to be a member of Haumea's collisional family. 2026 ED138 was missed by earlier surveys because it lies far south and near the crowded regions of the Galactic plane. Our recoveries of the known TNOs with H_V<4 suggest that about 3 more objects like them, and probably more, remain undiscovered away from the Galactic plane. More such objects probably lie within 10^∘ of the plane, which no search has yet covered to this depth.
ER -