Discovery and dynamics of a Sedna-like object with a perihelion of 66 au

TL;DR

The discovery of the Sedna-like TNO 2023 KQ14 ('Ammonite') with a unique orbit provides new insights into the early solar system and supports the existence of a distant planet influencing trans-Neptunian objects.

Contribution

This paper reports the discovery of a new Sedna-like object with a unique orbit that fills a gap in the observed distribution and offers evidence for a primordial orbital clustering.

Findings

Ammonite's orbit is dynamically stable over 4.5 billion years.

It fills the previously unexplained 'q-gap' in TNO distribution.

Supports the existence of a large, distant planet in the solar system.

Abstract

Trans-Neptunian objects (TNOs) with large perihelion distances ($q > 60$ au) and semi-major axes ($a > 200$ au) provide insights into the early evolution of the solar system and the existence of a hypothetical distant planet. These objects are still rare and their detection is challenging, yet they play a crucial role in constraining models of solar system formation. Here we report the discovery of a Sedna-like TNO, 2023\,KQ$_{14}$, nicknamed `Ammonite', with $q = 66$ au, $a = 252$ au, and inclination $i=11^\circ$. Ammonite's orbit does not align with those of the other Sedna-like objects and fills the previously unexplained `$q$-gap' in the observed distribution of distant solar system objects. Simulations demonstrate that Ammonite is dynamically stable over 4.5 billion years. % with less than 1\% variation in its semi-major axis. Our analysis suggests that Ammonite and the other Sedna-like objects may have shared a primordial orbital clustering around 4.2 billion years ago. Furthermore, Ammonite's stable orbit favors larger orbits ($\sim$ 500 au) rather than closer ones for a large hypothetical planet in present-day trans-Neptunian space.