Cometary dust: the diversity of primitive refractory grains

Abstract

Comet dust is primitive and shows significant diversity. Our knowledge of the properties of primitive cometary particles has expanded significantly through microscale investigations of cosmic dust samples (anhydrous interplanetary dust particles (IDPs), chondritic porous (CP) IDPs and UltraCarbonaceous Antarctic micrometeorites, Stardust and Rosetta), as well as through remote sensing (Spitzer IR spectroscopy). Comet dust are aggregate particles of materials unequilibrated at submicrometre scales. We discuss the properties and processes experienced by primitive matter in comets. Primitive particles exhibit a diverse range of: structure and typology; distribution of constituents; concentration and form of carbonaceous and refractory organic matter; Mg- and Fe-contents of the silicate minerals; sulfides; existence/abundance of type II chondrule fragments; high-temperature calcium–aluminium inclusions and ameboid-olivine aggregates; and rarely occurring Mg-carbonates and magnetite, whose explanation requires aqueous alteration on parent bodies. The properties of refractory materials imply there were disc processes that resulted in different comets having particular selections of primitive materials. The diversity of primitive particles has implications for the diversity of materials in the protoplanetary disc present at the time and in the region where the comets formed.This article is part of the themed issue ‘Cometary science after Rosetta’.

Analogues of interplanetary dust particles to interpret the zodiacal light polarization

“…This kind of materials were found in cometary comae particles together with CC, as shown by remote or in-situ observations (see e.g. Wooden et al, 2017). Our past and present laboratory measurements with PROGRA2 (Hadamcik et al, 2007a;2009b) have shown the importance of the presence of carbonaceous particles when trying to simulate cometary particles (with a global low-albedo).…”

“…Their precise composition (relative ratio of different elements, structure of the grains in the particles) can give some insight on their origin in the early solar system. The main technique to access their composition is remote or in-situ infrared spectroscopy compared to laboratory studies of collected particles (Hanner and Bradley, 2004 and references therein;Wooden et al, 2017). Cometary dust represents an un-equilibrated, heterogeneous mixture of crystalline and glassy or amorphous silicate minerals, organic refractory materials, and other constituents such as iron sulphide and possibly minor amount of iron oxides.…”

Fine‐grained material associated with a large sulfide returned from Comet 81P/Wild 2

“…Wooden et al. () recently tied together several lines of evidence pointing to late formation of Wild 2 materials, several Mya the onset of CAI formation. These include an abundance of objects with O isotopic signatures close to the terrestrial value, and an overabundance of late stage objects including Fe‐rich type II chondrules, and late Al dates (Ogliore et al.…”

Cometary science after Rosetta

“…Diane Wooden (NASA Ames Research Center) presented her overview on the diversity of primitive cometary dust particles and their implications for understanding conditions in the early Solar System [34]. Karl Battams (Naval Research Laboratory, USA) addressed the topic of objects that experience extreme conditions: sungrazers and sunskirters that venture much closer to the Sun than most comets that are observed from the Earth [35].…”