A collisionless scenario for Uranus tilting

TL;DR

This paper proposes a collisionless mechanism during planetary migration, involving a temporary satellite and inclination, to explain Uranus' high obliquity, challenging impact-based theories.

Contribution

It introduces a novel scenario where Uranus' tilt results from migration dynamics and satellite interactions, not a giant impact.

Findings

Uranus' obliquity can be generated without collisions.

A temporary satellite can induce the tilt during migration.

The satellite is ejected after the tilt, consistent with current observations.

Abstract

The origin of the high inclination of Uranus' spin-axis (Uranus' obliquity) is one of the great unanswered questions about the Solar system. Giant planets are believed to form with nearly zero obliquity, and it has been shown that the present behaviour of Uranus' spin is essentially stable. Several attempts were made in order to solve this problem. Here we report numerical simulations showing that Uranus' axis can be tilted during the planetary migration, without the need of a giant impact, provided that the planet had an additional satellite and a temporary large inclination. This might have happened during the giant planet instability phase described in the Nice model. In our scenario, the satellite is ejected after the tilt by a close encounter at the end of the migration. This model can both explain Uranus' large obliquity and bring new constraints on the planet orbital evolution.