# Model of Neptune's protoplanetary disk forming in-situ its surviving regular satellites after Triton's capture and comparison of the protoplanetary disks of the four gaseous giants

## TL;DR

This study models Neptune's protoplanetary disk to understand its formation and the impact of Triton's capture, revealing similarities with Uranus's disk despite unique features caused by moon interactions.

## Contribution

It introduces an isothermal oscillatory density model for Neptune's primordial disk, accounting for the effects of Triton's capture and comparing it with other gaseous giants' disks.

## Key findings

- Neptune's disk has a steep power-law density profile (k=-3.0).
- The disk's radial extent is smaller than Uranus's, likely truncated by Triton.
- Neptune's core density and rotation are comparable to Uranus's.

## Abstract

We fit an isothermal oscillatory density model of Neptune's protoplanetary disk to the surviving regular satellites and its innermost ring and we determine the radial scale length of the disk, the equation of state and the central density of the primordial gas, and the rotational state of the Neptunian nebula. Neptune's regular moons suffered from the retrograde capture of Triton that disrupted the system. Some moons may have been ejected, while others may have survived inside their potential minima. For this reason, the Neptunian nebula does not look like any of the nebulae that we modeled previously. In particular, there must be two density maxima deep inside the core of the nebula where no moons or rings are found nowadays. Even with this strong assumption, the recent discovery of the minor moon N XIV complicates further the modeling effort. With some additional assumptions, the Neptunian nebula still shares many similarities with the Uranian nebula, as was expected from the relative proximity and similar physical conditions of the two systems. For Neptune's primordial disk, we find a steep power-law index ($k=-3.0$), needed to accommodate the arrangement of the outer moons Larissa, N XIV, and Proteus. The rotation parameter that measures centrifugal support against self-gravity is quite small ($\beta_0=0.00808$), as is its radial scale length (13.6 km). The extent of the disk ($R_{\rm max}=0.12$ Gm) is a lot smaller than that of Uranus ($R_{\rm max}=0.60$ Gm) and Triton appears to be responsible for the truncation of the disk. The central density of the compact Neptunian core and its angular velocity are higher than but comparable to those of Uranus' core. In the end, we compare the models of the protoplanetary disks of the four gaseous giants.