Discovery and Dynamics of a New Sedna-like Object with a Perihelion of 66 au in the FOSSIL project

We report the results on a newly identified Extreme Trans-Neptunian Object (TNO) with Sedna-like characteristics. This object, discovered in the Formation of the Outer Solar System: An Icy Legacy (FOSSIL) project, was first detected in May 2023, with precovery in March 2023 and tracking in August 2023. Additional data from CFHT DDT in July 2024 and archived data extend the total observation arc to 10.1 years, revealing orbital parameters similar to known Sedna-like objects. The initial barycentric orbital elements are a = 251.86±0.28 au, e = 0.7383±0.0003, i = 10.98 degrees, q = 66 au. Its longitude of perihelion does not cluster with most currently known extreme TNOs (a > 150, q > 42).

Our team has performed orbital integrations to understand its long-term dynamical behavior. Using different integrators to ensure robustness in our findings, we have tracked the stability of orbital elements over a span of +4.5 Gyr. Based on the initial orbital elements and covariance matrix, the semimajor evolution (a/a0) of representative clones (highest, lowest a and best-fit a) is smaller than 1%. The inclination evolution oscillates between 8 and 11 degrees. According to previous literature, three known Sedna-like objects exhibit clustering of their primordial longitude of perihelion. Our backward integrations suggest that this newly discovered object also clusters with the other three Sedna-like objects. This clustering is estimated to have occurred around -4.2 Gyr, roughly a few hundred million years after the formation of the Solar System.