The Maximum Mass Solar Nebula and the early formation of planets

TL;DR

This paper introduces the concept of the Maximum Mass Solar Nebula, emphasizing early disc formation's role in planet formation, and suggests that most protoplanetary discs are already capable of forming planets due to early large planetesimal formation.

Contribution

It presents a new framework linking star and disc formation, highlighting the importance of early disc mass and transient spiral arms in planetesimal formation.

Findings

Protoplanetary discs start in a self-gravitating state with transient spiral arms.

Spiral arms efficiently trap dust, aiding planetesimal formation.

Most observable discs are already capable of hosting planets.

Abstract

Current planet formation theories provide successful frameworks with which to interpret the array of new observational data in this field. However, each of the two main theories (core accretion, gravitational instability) is unable to explain some key aspects. In many planet formation calculations, it is usual to treat the initial properties of the planet forming disc (mass, radius, etc.) as free parameters. In this paper, we stress the importance of setting the formation of planet forming discs within the context of the formation of the central stars. By exploring the early stages of disc formation, we introduce the concept of the Maximum Mass Solar Nebula (MMSN), as opposed to the oft-used Minimum Mass Solar Nebula (here mmsn). It is evident that almost all protoplanetary discs start their evolution in a strongly self-gravitating state. In agreement with almost all previous work in this area, we conclude that on the scales relevant to planet formation these discs are not gravitationally unstable to gas fragmentation, but instead form strong, transient spiral arms. These spiral arms can act as efficient dust traps allowing the accumulation and subsequent fragmentation of the dust (but not the gas). This phase is likely to populate the disc with relatively large planetesimals on short timescales while the disc is still veiled by a dusty-gas envelope. Crucially, the early formation of large planetesimals overcomes the main barriers remaining within the core accretion model. A prediction of this picture is that essentially all observable protoplanetary discs are already planet hosting.