Saturn Forms by Core Accretion in 3.4 Myr

TL;DR

This study presents two in situ core accretion simulations for Saturn, demonstrating that at large distances, core growth rate primarily controls formation timescale, with results aligning with observed disk lifetimes.

Contribution

The paper introduces two new core accretion models for Saturn that show similar formation timescales despite different opacity assumptions, highlighting the dominant role of core growth rate.

Findings

Both models produce ~3.4 Myr formation timescales.

Core growth rate limits planet formation at large distances.

Results suggest applicability to Uranus and Neptune.

Abstract

We present two new in situ core accretion simulations of Saturn with planet formation timescales of 3.37 Myr (model S0) and 3.48 Myr (model S1), consistent with observed protostellar disk lifetimes. In model S0, we assume rapid grain settling reduces opacity due to grains from full interstellar values (Podolak 2003). In model S1, we do not invoke grain settling, instead assigning full interstellar opacities to grains in the envelope. Surprisingly, the two models produce nearly identical formation timescales and core/atmosphere mass ratios. We therefore observe a new manifestation of core accretion theory: at large heliocentric distances, the solid core growth rate (limited by Keplerian orbital velocity) controls the planet formation timescale. We argue that this paradigm should apply to Uranus and Neptune as well.