Detlef Rost

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed (∼180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Properties of Interplanetary Dust: Information from Collected Samples

The properties of hundreds of interplanetary particles have been determined by direct laboratory analysis of recovered samples. The particles that span the 1 μm to 1 mm size range have been collected from the stratosphere, from polar ice, and from deep sea sediments. Typically, these particles are black, somewhat porous and have chondritic elemental compositions. They are rather complex mineral assemblages in that they are mixtures of very large numbers of sub-micrometer-sized components. While the data are not totally representative of small interplanetary meteoroids at 1 AU they provide significant insight into the common physical properties of meteoroids. These properties can be used as guidelines for analysis of spacecraft and astronomical observations and for modeling solar system dust as well as some circumstellar dust in systems around other stars.

Evidence for boron incorporation into the serpentine crystal structure

Abstract Serpentinite mud volcanoes from the Mariana forearc comprise B-rich mantle wedge peridotites serpentinized by slab fluids. The major component of these rocks are serpentine group minerals [Mg3Si2O5(OH)4], showing highly variable textural and geochemical features. Micro-Raman spectroscopy reveals that the serpentine minerals are well-crystallized lizardite and chrysotile. In situ SIMS spot analyses and element mapping via ToF-SIMS show that B is evenly distributed across serpentine grains, suggesting that serpentine, both lizardite and chrysotile in different textural regions, can host significant amounts of B (up to -200 μg/g) into its crystal structure. As such structurally bound B can only be released during recrystallization or serpentine breakdown, our results have implications for modeling of the efficiency of cross-arc fluid mobile element recycling in subduction zones and stress the importance of the hydrated forearc mantle as a reservoir for fluid mobile elements.

Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements

Abstract The presence of boron in the structure of diamond is rare in nature, and even when present, reported values are ≤0.5 ppm. This study used various spectroscopic methods and time-of-fight (ToF-) SIMS to characterize and analyze for boron in natural type IIb blue diamonds, including the well-known Hope and the Blue Heart diamonds, and on one high-pressure, high-temperature annealed natural stone. Infrared spectroscopy measurements reveal uncompensated boron values as large as 1.72 ± 0.15 ppm, which is significantly higher than the previously reported maximum of 0.5 ppm. ToF-SIMS analyses gave spot total boron concentrations as high as 8.4 ± 1.1 ppm for the Hope diamond to less than 0.08 ppm in other blue diamonds. By comparison, a type Ia diamond did not show detectable boron. ToF-SIMS analyses revealed strong zoning of boron in some diamonds, which was confirmed by mapping the uncompensated boron using synchrotron infrared spectroscopy. This greater range of boron concentrations compared to previous studies might be explained by the larger number of natural diamonds analyzed here, 78, compared to <10 samples reported in the literature. The samples in this study are all gem-quality diamonds, including some Intense to Fancy-Deep blue diamonds; color intensity, however, only loosely correlates with the boron content. Boron is also likely responsible for the phosphorescence emissions of type IIb diamonds, in the red at 660 nm and in the blue-green at 500 nm. Our results are consistent with previous work suggesting that the emissions are caused by donor-acceptor pair recombination processes involving boron and other defects. The exact nature of the phosphorescence processes is still not fully understood, but likely involves complex steps of charge carrier trapping and detrapping.

Improvements in quantification accuracy of inorganic time‐of‐flight secondary ion mass spectrometric analysis of silicate materials by using C60 primary ions

Time-of-flight secondary ion mass spectrometry is a very useful tool for the comprehensive characterization of samples by in situ measurements. A pulsed primary ion beam is used to sputter secondary ions from the surface of a sample and these are then recorded by a time-of-flight mass spectrometer. The parallel detection of all elements leads to very efficient sample usage allowing the comprehensive analysis of sub-micrometre sized samples. An inherent problem is accurate quantification of elemental abundances which mainly stems from the so-called matrix effect. This effect consists of changes in the sputtering and ionization efficiencies of the secondary neutrals and ions due to different sample compositions, different crystal structure or even different crystallographic orientations. Here we present results obtained using C60 molecules as a new primary ion species for inorganic analyses. The results show an improvement in quantification accuracy of elemental abundances, achieving relative errors as small as the certified uncertainties for the analyzed silicate standards. This improvement is probably due to the different sputter mechanism for C60+ primary ions from that for single atomic primary ions such as Ga+, Cs+ or Ar+. The C60+ cluster breaks up on impact, distributing the energy between its constituent carbon atoms. In this way it excavates nano-craters, rather than knocking out single atoms or molecules from the surface via a collision cascade, leading to a more reproducible sputter process and much improved quantification.

Determination of relative sensitivity factors during secondary ion sputtering of silicate glasses by Au+, Au+2 and Au+3 ions

In recent years, Au-cluster ions have been successfully used for organic analysis in secondary ion mass spectrometry. Cluster ions, such as Au(2)(+) and Au(3)(+), can produce secondary ion yield enhancements of up to a factor of 300 for high mass organic molecules with minimal sample damage. In this study, the potential for using Au(+), Au(2)(+) and Au(3)(+) primary ions for the analysis of inorganic samples is investigated by analyzing a range of silicate glass standards. Practical secondary ion yields for both Au(2)(+) and Au(3)(+) ions are enhanced relative to those for Au(+), consistent with their increased sputter rates. No elevation in ionization efficiency was found for the cluster primary ions. Relative sensitivity factors for major and trace elements in the standards showed no improvement in quantification with Au(2)(+) and Au(3)(+) ions over the use of Au(+) ions. Higher achievable primary ion currents for Au(+) ions than for Au(2)(+) and Au(3)(+) allow for more precise analyses of elemental abundances within inorganic samples, making them the preferred choice, in contrast to the choice of Au(2)(+) and Au(3)(+) for the analysis of organic samples. The use of delayed secondary ion extraction can also boost secondary ion signals, although there is a loss of overall sensitivity.

Subduction zone forearc serpentinites as incubators for deep microbial life

Significance We document organic matter encapsulated in rock clasts from a oceanic serpentinite mud volcano above the Izu–Bonin–Mariana subduction zone (Pacific Ocean). Although we cannot pinpoint the exact origin of the organic matter, chemical analysis of the constituents resembles molecular signatures that could be produced by microbial life deep within or below the mud volcano. Considering the known temperature limit for life, 122 °C, and the subduction zone forearc geotherm where such mud volcanoes are located, we estimate that life could exist as deep as ∼10,000 m below the seafloor. This is considerably deeper than other active serpentinizing regions such as midocean ridges and could have provided sheltered ecosystems for life to survive the more violent phases of Earth’s history. Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu–Bonin–Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni–Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth’s largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth’s history such as the late heavy bombardment and global mass extinctions.

Mineral-specific trace element contents of interplanetary dust particles

Abstract Sections of interplanetary dust particles (IDPs) have been analyzed with proton-induced X-ray emission (PIXE) and scanning transmission ion microscopy (STIM) in order to determine trace element contents and distributions on a micrometer scale as well as particle densities and masses. To accomplish this, several improvements of the proton microprobe and of the data acquisition system, as well as special sample preparation were necessary.

Nuclear astrophysics with CHILI

We recently completed CHILI (Chicago Instrument for Laser Ionization), a laser resonant ionization mass spectrometer that will be capable of a lateral resolution of 10 nm, a useful yield (atoms detected per atom removed from the sample) of 30–50%, and nearly complete suppression of interfering monatomic and molecular ions [1]. CHILI is equipped with six tunable lasers, allowing simultaneous measurement of the isotopic compositions of three elements. As part of the initial testing of CHILI, we plan a number of measurements that can constrain stellar nucleosynthesis models. (1) Simultaneous Sr, Zr, and Ba isotopic measurements of mainstream SiC grains will allow deeper understanding of observational constraints on the masses and internal 13C distributions of 13C pockets in AGB stars [2]. (2) Simultaneous Cr, Fe, and Ni isotopic measurement of mainstream grains will probe the effects of galactic chemical evolution on the initial isotopic compositions of AGB stars. (3) Simultaneous Ti, Zr, and Mo isotopic measurements of carbide inclusions within presolar graphite will constrain timescales of grain formation around AGB stars and mixing in Type II supernova ejecta. (4) Mapping of primitive meteorites for Sr, Zr, and Mo isotopes might reveal new types of presolar grains, including those responsible for r-process enrichments seen in some progressive chemical leaching experiments.