Actinide colloids and particles of environmental concern

We present the computational analysis of the 7.6 - 13.2 micrometer infrared (IR) spectrophotometry (R approximately equal to 120) of comet C/1995 O1 (Hale-Bopp) in conjunction with concurrent observations which extend the spectral energy distribution from the near-infrared to far-infrared wavelengths. The observations include temporal epochs pre-perihelion, (1996 October UT and 1997 February UT), near perihelion (1997 April UT), and postperihelion (1997 June UT). Through the computational modeling of small amorphous carbon, and crystalline and amorphous silicate grains in Hale-Bopp's coma, we find that as the comet approached perihelion, the grain size distribution (the Hanner modified power law) steepened (N = 3.4 pre-perihelion, to N = 3.7 near and post-perihelion) along with an increase in the fractal porosity of larger (greater than 1 micrometer) grains. The peak of the grain size distribution remained constant (ap = 0.2 micrometer) at each epoch. We attribute the emergence of the 9.3 micrometer peak near perihelion to crystalline orthopyroxeno grains released from inside the nucleus. Crystalline silicates (olivine and orthopyroxene) make up about 30% (by mass) of the submicron sized (less than 1 micrometer) dust grains in Hale-Bopp's coma during each epoch.

Grain Properties of Comet C/1995 O1 (Hale-Bopp) Deduced Through Computational Techniques

We report combined micro-infrared, micro-Raman, and field emission scanning electron microscope (FESEM) analyses of particles collected by the Stardust spacecraft during its flyby of comet 81P/Wild 2 on 2 January 2004 and successfully returned back to Earth on 15 January 2006. We present mid-infrared (IR) spectra of six of these particles. The CH2/CH3 ratios inferred from the infrared data are greater than those seen in organics in the diffuse interstellar medium, possibly indicating the presence of longer or less branched aliphatic chains. The micro-Raman data offer insights into the state of the order of the carbonaceous component present in the particles. Raman parameters for most of the particles span a similar range to that observed in interplanetary dust particles (IDPs) and the most primitive meteorites. Both the IR and Raman data imply the presence of a very labile carbonaceous component. Hydrated silicates may be present in two particles of Track 35, one of which may also contain carbonates, but further investigations with other techniques need to be performed to confirm these findings. In some cases, the analyses are difficult to interpret because of the presence of compressed aerogel mixed with the grains.

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Combined micro-Raman, micro-infrared, and field emission scanning electron microscope analyses of comet 81P/Wild 2 particles collected by Stardust

Laser mass spectrometry is a powerful tool for the sensitive, selective, and spatially resolved analysis of organic compounds in extraterrestrial materials Using microprobe two-step laser mass spectrometry (μL2MS), we have explored the organic composition of many different exogenous materials, including meteorites, interplanetary dust particles, and interstellar ice analogs, gaining significant insight into the nature of extraterrestrial materials Recently, we applied μL2MS to analyze the effect of heating caused by hypervelocity particle capture in aerogel, which was used on the NASA Stardust Mission to capture comet particles We show that this material exhibits complex organic molecules upon sudden heating Similar pulsed heating of carbonaceous materials is shown to produce an artifactual fullerene signal We review the use of μL2MS to investigate extraterrestrial materials, and we discuss its recent application to characterize the effect of pulsed heating on samples of interest

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Laser mass spectrometric detection of extraterrestrial aromatic molecules: Mini-review and examination of pulsed heating effects

We have used synchrotron Fe-XANES, XRS, micro Raman, and SEM-TEM analyses of Stardust track 41 slice and track 121 terminal area slices to identify Fe oxide (magnetite-hematite and amorphous oxide). Fe-Ti oxide, and V-rich chromite (Fe-Cr-V-Ti-Mn oxide) grains ranging in size from 200 nm to similar to ~10 μm. They co-exist with relict FeNi metal. Both Fe-XANES and microRaman analyses suggest that the FeNi metal and magnetite(Fe2O3FeO) also contain some hematite (Fe2O3). The FeNi has been partially oxidized (probably during capture), but on the basis of our experimental work with a light-gas gun and microRaman analyses, we believe that some of the magnetite-hematite mixtures may have originated on Wild 2. The terminal samples from track 121 also contain traces of sulfide and Mg-rich silicate minerals. Our results show an unequilibrated mixture of reduced and oxidized Fe-bearing minerals in the Wild 2 samples in an analogous way to mineral assemblages seen in carbonaceous chondrites and interplanetary dust particles. The samples contain some evidence for terrestrial contamination, for example, occasional Zn-bearing grains and amorphous Fe oxide in track 121 for which evidence of a cometary origin is lacking.

Z. Djouadi

Papers

In-situ Fe XANES of extraterrestrial grains trapped in aerogel collectors: An analytical test for the interpretation of Stardust samples analyses

Synchrotron X-rays in situ analysis of extraterrestrial grains trapped in aerogel

In-situ analyses of extraterrestrial grains trapped in aerogel.