Biomedical subjects

Jochen Kissel

Publications and source records attributed to Jochen Kissel.

6 recordsLinked to original sources

PubMed2006

Impact features on Stardust: implications for comet 81P/Wild 2 dust.

Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth. The morphologies of these surprisingly diverse features were created by particles varying from dense mineral grains to loosely bound, polymineralic aggregates ranging from tens of nanometers to hundreds of micrometers in size. The cumulative size distribution of Wild 2 dust is shallower than that of comet Halley, yet steeper than that of comet Grigg-Skjellerup.

Journal Article↗

PubMed2006

Comet 81P/Wild 2 under a microscope.

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Journal Article↗

PubMed2006

Xenomict energy in cold solids in space.

Minerals on earth whose crystalline order has been reduced by radioactive decay of contained atoms are termed "metamict." They are rare and few because in most crystalline solids, atoms and vacancies are relatively mobile at terrestrial temperatures, and radiation damage tends to be self-annealing. This is not the case in the extreme cold of deep space. Below roughly 100 K, reduced vacancy mobility allows cosmic ray and solar wind induced lattice defects to endure and accumulate for eons, reaching energy densities of up to MJ kg(-1) in some materials. We examine the possible effects of the release of energy stored in cold deep-space materials when solid-state defects recombine upon warming due to impacts, gravitational infall, or perihelion. Dimensional analysis suggests energetic defect recombination in radiation-damaged "xenomict" solids in comets, and planetesimals may, in some circumstances, raise internal temperatures enough to melt ice and volatilize frozen gases. We speculate that this may account for some cometary outbursts and Deep Impact experiment results. Calorimetric experiments on appropriately irradiated natural and synthetic materials are needed to further quantify these mechanisms.

Cold Temperature↗

PubMed2006

Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary material by COSIMA onboard ROSETTA.

Chemometric data evaluation methods for time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been tested for the characterization and classification of minerals. Potential applications of these methods include the expected data from cometary material to be measured by the COSIMA instrument onboard the ESA mission ROSETTA in the year 2014. Samples of the minerals serpentine, enstatite, olivine, and talc have been used as proxies for minerals existing in extraterrestrial matter. High mass resolution TOF-SIMS data allow the selection of peaks from inorganic ions relevant for minerals. Multivariate cluster analysis of peak intensity data by principal components analysis and the new method CORICO showed a good separation of the mineral classes. Classification by k nearest-neighbor classification (KNN) or binary decision trees (CART method) results in more than 90% correct class assignments in a leave-one-out cross validation.

Journal Article↗

PubMed2004

Surface of young Jupiter family comet 81P/Wild 2: view from the Stardust Spacecraft.

Images taken by the Stardust mission during its flyby of 81P/Wild 2 show the comet to be a 5-kilometer oblate body covered with remarkable topographic features, including unusual circular features that appear to be impact craters. The presence of high-angle slopes shows that the surface is cohesive and self-supporting. The comet does not appear to be a rubble pile, and its rounded shape is not directly consistent with the comet being a fragment of a larger body. The surface is active and yet it retains ancient terrain. Wild 2 appears to be in the early stages of its degradation phase as a small volatile-rich body in the inner solar system.

Cosmic Dust↗

PubMed2004

Assignment of quinone derivatives as the main compound class composing 'interstellar' grains based on both polarity ions detected by the 'Cometary and Interstellar Dust Analyser' (CIDA) onboard the spacecraft STARDUST.

The 'Cometary and Interstellar Dust Analyser' (CIDA) is a particle impact time-of-flight mass spectrometer onboard the NASA spacecraft STARDUST. A series of positive and negative ion mass spectra from the impact of (apparently) interstellar dust particles has been collected since 1999. In the meantime laboratory work has been performed to better understand the ion formation processes of organic grains impacting at those speeds (>15 km/s) and to relate them to some other ion formation methods. The key ion types were the negative ions, with some additional information from the positive ions. Here, first the principal ion formation rules are briefly reviewed. Secondly, the common substance class is inferred mainly by the application of exclusion principles, and appears to be partly condensed aromatic and quinonoid compounds with high oxygen and low nitrogen content. Oxygen appears to be present in quinone-type structures with condensed aromatic rings, possibly with furan substructures and some hydroxyl moieties. Some nitrogen may be present in pyrrole- or quinoline-type structures. Considerations of thermodynamics and radiation physics of these dust particles within the solar system are consistent with this interpretation. Quinoenzyme cofactors such as the known compound pyrroloquinoline-quinone (PQQ) and its subconstituents would be expected to yield similar mass spectra.

Dust↗