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Primordial Orbital Clustering of Sednoids

Presentation #202.09 in the session TNO Theory and Physical Properties (Oral Presentation)

Published onOct 23, 2023
Primordial Orbital Clustering of Sednoids

We have been studying Solar System histories that involve the early brief presence of a rogue planet (Huang et al 2022, ApJL, 938). In those models an ‘iceberg’ of large-perihelion (q > 50 au) TNOs with semimajor axes beyond 200 au are produced. We observe that iceberg TNOs with extremely high perihelia (q > 120 au) have not yet had time to homogenize their perihelion directions due to differential precession, and compute where on the sky such objects will preferentially be detected. This work motivated us to examine the past history of the three most detached TNOs — Sedna, 2012 VP113, and Leleakuhonua — also collectively known as Sednoids. By integrating backwards their nominal and cloned orbits for the Solar System’s age, we surprisingly found that the only time their apsidal lines were clustered was 4.5 billion years ago (at perihelion longitude of 200 degrees with circular variance of 8 degrees). This “primordial orbital clustering” is independent of the observational biases that contribute to the current on-sky clustering in the large-a Kuiper Belt. If future Sednoid discoveries confirm these findings, this strongly argues for an initial early event which imprinted this particular apsidal orientation on the early detached TNO populations; it has been modified only by the expected precession from the 4 giant planets over the last 4 Gyr. The rogue planet model naturally produces this signature, but other scenarios that could potentially create it include a dominant close-in stellar flyby 4.5 Gyr ago or self-gravity of a massive primordial scattering disk.

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