Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets

TL;DR

This paper investigates the peculiar orbital distribution of extreme trans-Neptunian objects (ETNOs) and suggests that their observed properties, explained by the Kozai mechanism, imply the existence of at least two undiscovered trans-Plutonian planets.

Contribution

It provides evidence supporting the presence of multiple unseen planets beyond Neptune based on the orbital characteristics of ETNOs and the Kozai mechanism.

Findings

Observed excess of ETNOs near the ascending node is not due to observational bias.

The orbital distribution of ETNOs is consistent with shepherding by unseen planets.

Analysis suggests at least two trans-Plutonian planets likely exist.

Abstract

The existence of an outer planet beyond Pluto has been a matter of debate for decades and the recent discovery of 2012 VP113 has just revived the interest for this controversial topic. This Sedna-like object has the most distant perihelion of any known minor planet and the value of its argument of perihelion is close to 0 degrees. This property appears to be shared by almost all known asteroids with semimajor axis greater than 150 au and perihelion greater than 30 au (the extreme trans-Neptunian objects or ETNOs), and this fact has been interpreted as evidence for the existence of a super-Earth at 250 au. In this scenario, a population of stable asteroids may be shepherded by a distant, undiscovered planet larger than the Earth that keeps the value of their argument of perihelion librating around 0 degrees as a result of the Kozai mechanism. Here, we study the visibility of these ETNOs and confirm that the observed excess of objects reaching perihelion near the ascending node cannot be explained in terms of any observational biases. This excess must be a true feature of this population and its possible origin is explored in the framework of the Kozai effect. The analysis of several possible scenarios strongly suggest that at least two trans-Plutonian planets must exist.