Constraints to Uranus' Great Collision. IV. The Origin of Prospero

TL;DR

This paper investigates whether Uranus's large obliquity resulted from a great collision and explores the origin of its irregular moon Prospero, analyzing capture mechanisms and their plausibility within planetary formation scenarios.

Contribution

It provides a detailed analysis of the collision hypothesis for Uranus's obliquity and evaluates potential formation mechanisms for Prospero, considering various timing and capture scenarios.

Findings

Prospero could not have existed during the collision event.

Capture of Prospero after the collision is dynamically challenging.

The collision hypothesis for Uranus's obliquity remains uncertain.

Abstract

It is widely accepted that the large obliquity of Uranus is the result of a great tangential collision (GC) with an Earth size proto-planet at the end of the accretion. We attempt to constraint the GC scenario as the cause of Uranus' obliquity as well as on the mechanisms able to give origin to the Uranian irregulars. Different capture mechanisms for irregulars operate at different stages on the giant planets formation process. The mechanisms able to capture the uranian irregulars before and after the GC are analysed. Assuming that they were captured before the GC, we calculate the orbital transfer of the nine irregulars by the impulse imparted by the GC. If their orbital transfer results dynamically implausible, they should have originated after the GC. We investigate and discuss the dissipative mechanisms able to operate later. In particular Prospero could not exist at the time of the GC. Different capture mechanisms for Prospero after the GC are investigated. Gas drag by Uranus'envelope and pull-down capture are not plausible mechanisms. Capture of Prospero through a collisionless interaction seems to be difficult. The GC itself provides a mechanism of permanent capture. However, the capture of Prospero by the GC is a low probable event. Catastrophic collisions could be a possible mechanism for the birth of Prospero and the other irregulars after the GC. Orbital and physical clusterings should then be expected. Either Prospero had to originate after the GC or the GC did not occur. In the former case, the mechanism for the origin of Prospero after the GC remains an open question. In the latter case, another theory to account for Uranus' obliquity and the formation of the Uranian regular satellites on the equatorial plane of the planet would be needed.