Two refractory Wild 2 terminal particles from a carrot‐shaped track characterized combining MIR/FIR/Raman microspectroscopy and FE‐SEM/EDS analyses

Abstract

Abstract-We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter-family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE-SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca-free and low-Ca, Mg-rich, Mg,Fe-olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni-free and low-Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE-SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE-SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.

GIADA: shining a light on the monitoring of the comet dust production from the nucleus of 67P/Churyumov-Gerasimenko

“…GIADA fluffy lowdensity aggregates analogs among the Wild 2 particles could be the volatile-rich aggregates producing bulbous tracks (type C, Hörz et al 2006), in the capturing aerogel, leaving organic IR features along the track and carbon-rich small fragments completely scattered throughout the track (Sandford et al 2006;Rotundi et al 2008). Compact GIADA particles can be associated with Wild 2 dense mineral grains, forming type A carrotlike thin trails (e.g., Hörz et al 2006;Rotundi et al 2014), and/or to cluster IDPs carving type B bulbous trails ending in stylus tracks (e.g., Hörz et al 2006;Rotundi et al 2008). Compact and dense particles with bulk density constrained in the range (1.9 ± 1.1) × 10 3 kg m −3 (Rotundi et al 2015;Fulle et al 2015b) and sizes (80 to 800 µm) that prevent their dynamics to be affected by coma and spacecraft potentials (Fulle et al 2015a).…”

Dynamics of non-spherical dust in the coma of 67P/Churyumov– Gerasimenko constrained by GIADA and ROSINA data

“…consistent with cometary mineralogy (e.g. Brownlee et al 2006;Brunetto et al 2011;Rotundi et al 2014). Taking into account the density constraints settled by GIADA data, we simulated the motion of 30 particles detected by GIADA during P1 and P2.…”

Rotating dust particles in the coma of comet 67P/Churyumov-Gerasimenko

“…All these models assume that the dust grains are spherical. However, the stratospheric interplanetary dust particles (IDPs; Rotundi et al 2007Rotundi et al , 2014 or the samples brought by the Stardust mission from comet 81P/Wild (Brownlee et al 2006;Zolensky et al 2006;Rotundi & Rietmeijer 2008) imply strongly irregular dust shapes by origin.…”