Pebble accretion at the origin of water in Europa

TL;DR

This paper models solids transport in the circum-Jovian disk to explain the water content of Europa, suggesting pebble accretion near the snowline as a key formation mechanism.

Contribution

It introduces a new model of solids transport considering multiple physical processes, explaining Europa's low water content through pebble accretion near the snowline.

Findings

Pebble water content aligns with Europa's observed water fraction.

Europa likely formed from dehydrated material inside the snowline.

Satellite migration was linked to snowline evolution.

Abstract

Despite the fact that the observed gradient in water content among the Galilean satellites is globally consistent with a formation in a circum-Jovian disk on both sides of the snowline, the mechanisms that led to a low water mass fraction in Europa ($\sim$$8\%$) are not yet understood. Here, we present new modeling results of solids transport in the circum-Jovian disk accounting for aerodynamic drag, turbulent diffusion, surface temperature evolution and sublimation of water ice. We find that the water mass fraction of pebbles (e.g., solids with sizes of 10$^{-2}$ -- 1 m) as they drift inward is globally consistent with the current water content of the Galilean system. This opens the possibility that each satellite could have formed through pebble accretion within a delimited region whose boundaries were defined by the position of the snowline. This further implies that the migration of the forming satellites was tied to the evolution of the snowline so that Europa fully accreted from partially dehydrated material in the region just inside of the snowline.