Outer solar system possibly shaped by a stellar fly-by

TL;DR

A stellar fly-by in the outer solar system can explain the peculiar distribution and orbits of TNOs and Sednoids, suggesting such events are more common than previously thought and may have shaped planetary characteristics.

Contribution

This study demonstrates through simulations that a stellar fly-by can account for the outer solar system's properties, challenging previous assumptions about the rarity of such events.

Findings

Fly-bys can produce the observed TNO distribution and Sednoid orbits.

Such events are more likely than previously estimated.

The scenario explains Neptune's higher mass compared to Uranus.

Abstract

The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.