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At least 37 records · Page 2Linked to original sources
PubMed1998

Carbonaceous micrometeorites from Antarctica.

Over 100 000 large interplanetary dust particles in the 50-500 micrometers size range have been recovered in clean conditions from approximately 600 tons of Antarctic melt ice water as both unmelted and partially melted/dehydrated micrometeorites and cosmic spherules. Flux measurements in both the Greenland and Antarctica ice sheets indicate that the micrometeorites deliver to the Earth's surface approximately 2000x more extraterrestrial material than brought by meteorites. Mineralogical and chemical studies of Antarctic micrometeorites indicate that they are only related to the relatively rare CM and CR carbonaceous chondrite groups, being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals. However, there are also marked differences between these two families of solar system objects, including higher C/O ratios and a very marked depletion of chondrules in micrometeorite matter; hence, they are "chondrites-without-chondrules." Thus, the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects, probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles, comets. One of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early Earth, and more recently, with the early history of the solar system.

Antarctic Regions↗
PubMed1994

Rapid assessment of radiobiological doses for terrestrial and interplanetary space missions.

This paper presents the doses levels expected in orbits in chart form, covering the range 300-800 km of altitude and 0-90 degrees of inclination behind shieldings similar to the Hermes spacecraft and the EVA spacesuit matter distributions. These charts allow users to rapidly find the radiobiological dose received in the most critical organs of the human body either in normal situations or during a large solar event. Outside the magnetosphere, during interplanetary or lunar missions, when the dose received during crossing of the radiation belts become negligible, the dose is due to galactic cosmic rays (GCR) and solar flares. The correct radiobiological assessment of the components of this radiation field becomes a major problem. On the Moon a permanent ground-based station can be shielded by lunar materials against meteoroids and radiations. The radiobiological hazard, essentially linked to the solar flare risk during the transfer phase and the extra-station activities, may be solved by mission planning. For interplanetary flights the problem comes from both increased risk of solar events and from the continuous exposure to GCR. These energetic particles cannot be easily stopped by shieldings; cost considerations imply that more effective materials must be used. Impact on the vehicle design and the mission planning is important.

Atlantic Ocean↗
PubMed2005

A large dust/ice ratio in the nucleus of comet 9P/Tempel 1.

Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ and remote measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5 10(32) water molecules or 4.5 10(6) kg) and the cross-section of the dust (330 km2 assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed. High dust velocities (between 110 m s(-1) and 300 m s(-1)) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts.

Journal Article↗
PubMed1997

Spectrum of 100-kyr glacial cycle: orbital inclination, not eccentricity.

Spectral analysis of climate data shows a strong narrow peak with period approximately 100 kyr, attributed by the Milankovitch theory to changes in the eccentricity of the earth's orbit. The narrowness of the peak does suggest an astronomical origin; however the shape of the peak is incompatible with both linear and nonlinear models that attribute the cycle to eccentricity or (equivalently) to the envelope of the precession. In contrast, the orbital inclination parameter gives a good match to both the spectrum and bispectrum of the climate data. Extraterrestrial accretion from meteoroids or interplanetary dust is proposed as a mechanism that could link inclination to climate, and experimental tests are described that could prove or disprove this hypothesis.

Journal Article↗
PubMed2004

Removal of meteoric iron on polar mesospheric clouds.

Polar mesospheric clouds are thin layers of nanometer-sized ice particles that occur at altitudes between 82 and 87 kilometers in the high-latitude summer mesosphere. These clouds overlap in altitude with the layer of iron (Fe) atoms that is produced by the ablation of meteoroids entering the atmosphere. Simultaneous observations of the Fe layer and the clouds, made by lidar during midsummer at the South Pole, demonstrate that essentially complete removal of Fe atoms can occur inside the clouds. Laboratory experiments and atmospheric modeling show that this phenomenon is explained by the efficient uptake of Fe on the ice particle surface.

Journal Article↗
PubMed2000

The fall, recovery, orbit, and composition of the Tagish Lake meteorite: a new type of carbonaceous chondrite.

The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.

Journal Article↗
PubMed1995

Metal ions in the atmosphere of Neptune.

Microwave propagation experiments performed with Voyager 2 at Neptune revealed sharp layers of electrons in Neptune's lower ionosphere with densities of approximately 10(4) per cubic centimeter. These layers are reminiscent of the sporadic-E layers in the Earth's ionosphere, and when taken together with data from the other giant planets, these data confirm the importance of the magnetic field in layer formation. A photochemical model that incorporates species produced by meteoroid ablation predicts that singly ionized magnesium is the most likely metal to be found in the layers, although laboratory data on the kinetics of metallic atoms and ions in a reducing environment are lacking. The metal chemistry discussed here is directly relevant to the abundant metals observed at the impact site of the G fragment of comet Shoemaker Levy 9 on Jupiter.

Atmosphere↗
PubMed1996

Thin foil preparation of metal particles in brittle ceramic matrices.

Thin foil preparation for metal particles in brittle ceramic matrices is particularly difficult, due to differential thinning of the component materials. This paper considers the preparation of thin foils of stony meteorites. Stony meteorites have a composite nature consisting of small metal particles (< 200 microns) embedded in an inherently brittle silicate matrix. Specimens of this type are difficult to prepare as thin foils because the area of interest is limited to specific regions within the metal particles. The problems of thin foil preparation of metal particles in the stony meteorites were overcome by developing a technique involving electrochemical polishing prior to ion beam thinning. The metal particles were first separated from the silicate matrix and then embedded in Epo-Tek H20E silver epoxy. This specific epoxy was selected for its good electron conductivity which allowed the specimen to be thinned by the electrochemical polishing technique. Specimens prepared by this technique have permitted the direct observation and characterization of the metallic phases in stony meteorites.

Ceramics↗
PubMed1996

Hydrothermal systems on Mars: an assessment of present evidence.

Hydrothermal processes have been suggested to explain a number of observations for Mars, including D/H ratios of water extracted from Martian meteorites, as a means for removing CO2 from the Martian atmosphere and sequestering it in the crust as carbonates, and as a possible origin for iron oxide-rich spectral units on the floors of some rifted basins (chasmata). There are numerous examples of Martian channels formed by discharges of subsurface water near potential magmatic heat sources, and hydrothermal processes have also been proposed as a mechanism for aquifer recharge needed to sustain long term erosion of sapping channels. The following geological settings have been identified as targets for ancient hydrothermal systems on Mars: channels located along the margins of impact crater melt sheets and on the slopes of ancient volcanoes; chaotic and fretted terranes where shallow subsurface heat sources are thought to have interacted with ground ice; and the floors of calderas and rifted basins (e.g. chasmata). On Earth, such geological environments are often a locus for hydrothermal mineralization. But we presently lack the mineralogical information needed for a definitive evaluation of hypotheses. A preferred tool for identifying minerals by remote sensing methods on Earth is high spatial resolution, hyperspectral, near-infrared spectroscopy, a technique that has been extensively developed by mineral explorationists. Future efforts to explore Mars for ancient hydrothermal systems would benefit from the application of methods developed by the mining industry to look for similar deposits on Earth. But Earth-based exploration models must be adapted to account for the large differences in the climatic and geological history of Mars. For example, it is likely that the early surface environment of Mars was cool, perhaps consistently below freezing, with the shallow portions of hydrothermal systems being dominated by magma-cryosphere interactions. Given the smaller gravitational field, declining atmospheric pressure, and widespread, permeable megaregolith on Mars, volatile outgassing and magmatic cooling would have been more effective than on Earth. Thus, hydrothermal systems are likely to have had much lower average surface temperatures than comparable geological settings on Earth. The likely predominance of basaltic crust on Mars suggests that hydrothermal fluids and associated deposits should be enriched in Fe, Mg, Si and Ca, with surficial deposits being dominated by lower temperature, mixed iron oxide and carbonate mineralogies.

Deuterium↗
PubMed1996

The transfer of viable microorganisms between planets.

There is increasing acceptance that catastrophic cosmic impacts have played an important role in shaping the history of terrestrial life. Large asteroid and cometary impacts are also capable of displacing substantial quantities of planetary surface material into space. The discovery of Martian rocks on Earth suggests that viable microorganisms within such ejecta could be exchanged between planets. If this conjecture is correct, it will have profound implications for the origin and evolution of life in the solar system.

Archaea↗
PubMed2002

Chemical markers for bacteria in extraterrestrial samples.

Interplanetary missions to collect pristine Martian surface samples for analysis of organic molecules, and to search for evidence of life, are in the planning phases. The only extraterrestrial samples currently on Earth are lunar dust and rocks, brought back by the Apollo (U.S.) and Luna (Soviet Union) missions to the moon, and meteorites. Meteorites are contaminated when they pass through the Earth's atmosphere, and during environmental exposure on Earth. Lunar fines have been stored on Earth for over 30 years under conditions designed to avoid chemical but not microbiological contamination. It has been extremely difficult to draw firm conclusions about the origin of chemicals (including amino acids) in extraterrestrial samples. Of particular concern has been the possibility of bacterial contamination. Recent work using state-of-the-art gas chromatography tandem mass spectrometry (GC-MS/MS) has dramatically lowered the chemical background, allowing a clear demonstration that lunar fines are remarkably different from terrestrial dust in that they generally lack certain chemical markers (muramic acid and 3-hydroxy fatty acids) characteristic of Earth's bacteria. Thus, lunar dust might be used as a negative control, in conjunction with GC-MS/MS analyses, in future analytical studies of lunar dust and meteorites. Such analyses may also be important in studies designed to search for the presence of life on Mars.

Amino Acids↗
PubMed2002

Antibodies directed against L and D isovaline using a chemical derivatizing reagent for the measurement of their enantiomeric ratio in extraterrestrial samples: first step-production and characterization of antibodies.

Determining the enantiomeric ratio of amino acids in meteorites requires very sensitive and precise measurements. In this study, an immunochemical approach, combined with new chemical derivatizing agents, was investigated for the measurement of the enantiomeric ratio of isovaline. In the initial step, L and D isovaline were derivatized with epsilon-benzyloxycarbonyl-L-lysine-(t-butyl ester)-chloroethylnitrosourea (Z-L-Lys-(OtBu)-CENU). The Z group was hydrolyzed and the resulting isovaline derivatives (L-Lys(OtBu)-L-isovaline and L-Lys(OtBu)-D-isovaline) were conjugated with protein using glutaraldehyde and reduced with sodium borohydride. Rabbits were immunized with the immunogenic conjugates thus obtained. Antibodies were characterized using many compounds, both derivatized and underivatized, in competitive ELISA tests. These competition experiments performed enabled us to establish the following results: 1) unconjugated L-Lys(OtBu)-L-isovaline and L-Lys(OtBu)-D-isovaline were poorly recognized; 2) all related L-Lys(OtBu)-alpha-hydrogenated amino acids (L and D) were not recognized at all, which eliminates the possibility of the measurements being distorted by contamination; 3) only conjugated L-Lys(OtBu)-alpha-amino-isobutyric acid (AIB) was recognized by the antibody, 4) the enantiomeric discrimination of L and D isovaline through their derivatives (diastereoisomeric L-Lys(OtBu)-L-isovaline and L-Lys(OtBu)-D-isovaline) was in accordance with the measurement of their enantiomeric ratio. Immunopurification was shown to enhance antibody specificity. The strategy employed shows potential for the quantification of meteoritic amino acids.

Animals↗
PubMed2001

Enantiomer separation of hydrocarbons in preparation for ROSETTA's "chirality-experiment".

Until now the favored method for separating racemic pairs of underivatized alcohols, diols, and phenylsubstituted amines has been gas chromatography on cyclodextrin phases. However, certain enantiomers of saturated chiral hydrocarbons could not be resolved in this way because they lack the functional groups necessary to undergo "intensive" diastereomeric interactions with the cyclodextrins. The present study describes a gas-chromatographic technique for resolution of saturated aliphatic hydrocarbons into their enantiomers and presents a brief discussion of the possible applications. The (enantiomer) separations were performed in preparation for the Cometary Sampling and Composition Experiment on board the cometary lander RoLand, part of ESA's cornerstone mission ROSETTA. This experiment has been designed to investigate the hypotheses that biomolecular asymmetry has an interstellar origin and to separate and identify a wide range of organic enantiomers in situ on the surface of a comet's nucleus.

Alkanes↗
PubMed2005

Supernova antineutrino interactions cause chiral symmetry breaking and possibly homochiral biomaterials for life.

There is some evidence that nonracemic hydrocarbons occur in meteorites. This would indicate an extraterrestrial origin of the homochirality in living systems (proteins, DNA, RNA). The weak interaction breaks chiral symmetry, but a robust process is needed. We propose that, in an SNII explosion, antineutrinos could provide this mechanism in the solar cloud. Pre-simple estimates of this possibility are given here.

Astronomical Phenomena↗