Direct measurement of decimeter-sized rocky material in the Oort cloud

TL;DR

This study reports the first direct detection of decimeter-sized rocky bodies in the Oort cloud, supporting models that predict rocky material is implanted in the outer Solar System during its formation.

Contribution

It provides the first direct observation and characterization of rocky meteoroids from the Oort cloud, confirming predictions of migration-based Solar System formation models.

Findings

Detected a decimeter-sized rocky meteoroid on a retrograde orbit.

Estimated rocky meteoroid flux impacting Earth from the Oort cloud.

Found rocky objects constitute about 6% of Oort cloud impactors.

Abstract

The Oort cloud is thought to be a reservoir of icy planetesimals and the source of long-period comets (LPCs) implanted from the outer Solar System during the time of giant planet formation. The abundance of rocky ice-free bodies is a key diagnostic of Solar System formation models as it can distinguish between ``massive" and ``depleted" proto-asteroid belt scenarios and thus disentangle competing planet formation models. Here we report a direct observation of a decimeter-sized ($\sim2$ kg) rocky meteoroid on a retrograde LPC orbit ($e \approx 1.0$, i = $121^{\circ}$). During its flight, it fragmented at dynamic pressures similar to fireballs dropping ordinary chondrite meteorites. A numerical ablation model fit produces bulk density and ablation properties also consistent with asteroidal meteoroids. We estimate the flux of rocky objects impacting Earth from the Oort cloud to be $1.08^{+2.81}_{-0.95} \mathrm{meteoroids/10^6 km^2/yr}$ to a mass limit of 10 g. This corresponds to an abundance of rocky meteoroids of $\sim6^{+13}_{-5}$\% of all objects originating in the Oort cloud and impacting Earth to these masses. Our result gives support to migration-based dynamical models of the formation of the Solar System which predict that significant rocky material is implanted in the Oort cloud, a result not explained by traditional Solar System formation models.