Enrichment of Jupiter's atmosphere by late planetesimal bombardment

TL;DR

This paper proposes that Jupiter's atmospheric enrichment with heavy elements resulted from late planetesimal accretion facilitated by significant orbital migration of proto-Jupiter from about 20 AU to its current position.

Contribution

The study demonstrates through modeling that Jupiter's migration enables late planetesimal accretion, explaining atmospheric enrichment inconsistent with in-situ formation models.

Findings

Migration from ~20 AU to current orbit is crucial for late accretion.

Late accretion can enrich the atmosphere if the outer layer is fully mixed and relatively thin.

In-situ formation models cannot account for observed enrichment without migration.

Abstract

Jupiter's atmosphere is enriched with heavy elements by a factor of about 3 compared to proto-solar. The origin of this enrichment and whether it represent the bulk composition of the planetary envelope remain unknown. Internal structure models of Jupiter suggest that its envelope is separated from the deep interior and that the planet is not fully mixed. This implies that Jupiter's atmosphere was enriched with heavy elements just before the end of its formation. Such enrichment can be a result of late planetesimal accretion. However, in-situ Jupiter formation models suggest the decreasing accretion rate with increasing planetary mass, which cannot explain Jupiter's atmospheric enrichment. In this study, we model Jupiter's formation and show that an migration of proto-Jupiter from $\sim$ 20 AU to its current location can lead to a late planetesimal accretion and atmospheric enrichment. Late planetesimal accretion does not occur if proto-Jupiter migrates only a few AU. We suggest that if Jupiter's outermost layer is fully-mixed and is relatively thin (up to $\sim$ 20\% of its mass), such late accretion can explain its measured atmospheric composition. It is therefore possible that Jupiter underwent significant orbital migration followed by late planetesimal accretion.