Oxygen Isotopic Composition of Coarse- and Fine-grained Material from Comet 81P/Wild 2

TL;DR

This study analyzes the oxygen isotopic compositions of particles from comet 81P/Wild 2, revealing insights into early Solar System materials and the comet's diverse origins.

Contribution

It provides the first detailed isotopic analysis of both coarse and fine particles from Wild 2, showing their compositional diversity and potential origins.

Findings

Large particles have narrow isotopic range similar to meteorites.

Fine particles exhibit a broad isotopic range, indicating diverse origins.

Results suggest Wild 2 contains both inner and outer Solar System materials.

Abstract

Individual particles from comet 81P/Wild 2 collected by NASA's Stardust mission vary in size from small sub-$\mu$m fragments found in the walls of the aerogel tracks, to large fragments up to tens of $\mu$m in size found towards the termini of tracks. The comet, in an orbit beyond Neptune since its formation, retains an intact a record of early-Solar-System processes that was compromised in asteroidal samples by heating and aqueous alteration. We measured the O isotopic composition of seven Stardust fragments larger than $\sim$2 $\mu$m extracted from five different Stardust aerogel tracks, and 63 particles smaller than $\sim$2 $\mu$m from the wall of a Stardust track. The larger particles show a relatively narrow range of O isotopic compositions that is consistent with $^{16}$O-poor phases commonly seen in meteorites. Many of the larger Stardust fragments studied so far have chondrule-like mineralogy which is consistent with formation in the inner Solar System. The fine-grained material shows a very broad range of O isotopic compositions ($-70<\Delta^{17}$O$<+60$) suggesting that Wild 2 fines are either primitive outer-nebula dust or a very diverse sampling of inner Solar System compositional reservoirs that accreted along with a large number of inner-Solar-System rocks to form comet Wild 2.