Experimentelle und Analytische Planetologie
TOF-SIMS, NanoSIMS, and TEM analysis of interplanetary dust particles - Preparation for the Stardust
cometary sample return mission
Before in 2006 the Stardust mission will bring material from comet Wild 2 under controlled conditions to Earth,
anhydrous IDPs represent probably the only source for cometary matter that is available for analysis in
terrestrial laboratories. Like meteorites, IDPs have their own individual history that links them to their respective
parent bodies and that can be revealed with modern analytical techniques. In most previous studies, only one
analytical technique has been applied to individual particles and averaged properties from different sub-sets of
the IDP collection were compared. Major technical developments during recent years provide the opportunity to
study individual particles with a great variety of analytical techniques.
For
a comprehensive study of small samples like IDPs a combination of different techniques is appropriate to yield a
maximum of information on single grains and their components. While isotopic anomalies within such grains
can easily be detected with NanoSIMS, TOF-SIMS allows a chemical and often mineralogical identification of
the respective carrier phases. With NanoSIMS alone, this would be impossible in case of very small samples
due to sample destruction.
Because of its characteristics, TOF-SIMS is
a suitable technique for the analysis of samples from the Stardust mission. Grains from comet Wild 2 as well as
contemporary interstellar dust are projected samples to be brought back in 2006. For both types of particles it is
indispensable to use analytical methods that introduce the least possible bias and that allow subsequent
analyses with other techniques. TOF-SIMS with its comprehensive analysis and the little sample destruction
meets these requirements.
In continuation of a comprehensive
consortium study of IDPs from stratospheric dust collector U2071, three particles were selected for TOF-SIMS,
NanoSIMS, and TEM analysis. Since 1994, when the consortium study was initiated, technical improvements in
both SIMS variants, especially in achievable lateral resolution and sensitivity have significantly enhanced the
abilities to study these tiny, extremely fine-grained, complex particles. U2071J2. TOF-SIMS
and TEM results yield typical sizes much lower than 1 µm for different phases within this heterogeneous
IDP. Several of these grains can be identified as olivine, pyroxene, and Fe,Ni-sulfides. Al-rich areas are probably
GEMS (glass with embedded metal and sulfides). Since there is no indication for the presence of hydrous
minerals, U2071J2 can be classified as an anhydrous IDP, a class that is often connected to comets. However,
NanoSIMS results show no indication of isotopic anomalies in oxygen or the presence of presolar matter. Most
element ratios relative to Si are below 1, an indication for the presence of residual silicone oil.
U2071C9 also shows heterogeneities
on a sub-micrometer scale. Olivine, pyroxene, and some Al-rich phases (probably feldspar, one also enriched in
S) were identified by TOF-SIMS and TEM. NanoSIMS analyses again show no isotopic anomalies.
U2071H1h mainly consists of a single Mg-rich
phase. Onion shell like distributions of OH, F, and S are strong hints for contamination.
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