Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Meteoroids”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed1995

The formation of organic molecules in astronomical ices.

An absorption feature at 3.4 micrometers has been observed in various lines-of-sight through the diffuse interstellar medium. Its position and width lead to an identification with the C-H stretching mode of solid organic material. A possible mechanism for the production of organic solids in the interstellar medium is UV photoprocessing of icy mantles which accrete on dust grains in dense clouds. Furthermore, thermally induced reactions involving formaldehyde molecules in the mantles could be an important source of organics. Laboratory simulation of these processes shows that a large variety of oxygen- and nitrogen-rich species may be produced. It is shown that the occurrence of periodic transient heating events plays an important role in the production of organic material in the ice mantles. Finally, it is pointed out how future missions like the Infrared Space Observatory (ISO) as well as analysis of comet material by Rosetta may be able to clarify the nature and evolution of interstellar organics.

Carbon Monoxide↗
PubMed1995

Radiation chemistry of ices of planetological interest at low temperature.

We present the results of recent experiments on some physico-chemical effects induced by fast ion colliding with solids of relevance for the physics of planetary objects. The production of molecular solids, polymer-like materials and amorphous carbon by irradiation of frozen hydrocarbons and pentacene is discussed. We also report on a set of experimental results obtained irradiating methanol and water-methanol mixtures. Because of bombardment different species form. The techniques used for the analysis are "in situ" infrared (IR) and Raman spectroscopy. The experimental results are finally discussed in the light of their relevance for planetary physics.

Cosmic Dust↗
PubMed1995

The electrolytical processes in dirty ices: implications for origin and chemistry of minor bodies and related objects.

Many moonlike bodies (M approximately or = 1 Moon) beyond the Martian orbit contain large amounts of dirty ice (approximately 50%) forming thick mantle with the solid phase thermal convection. When a body moves through the inter- or nearplanetary magnetized plasma, electric current is generated in the body and its environment. The current passing through a dirty ice containing up to 10% of organic admixtures produces a lot of electrochemical effects which have a profound impact on its composition. At this stage one can hardly say something definite concerning changes experienced by organics. The changes must occur inevitably and can be of a rather unexpected and far-reaching nature, so deserving a close study. Another obvious effect is a volumetric electrolysis of ice containing alien inclusions. The electrolysis products accumulate in ice in the form of a solid solution which is capable of detonation at 15-20 wt.% of 2H2 + O2. If M > or = 1 Moon (Galilean satellites, Titan), the body loses in explosion a part of its mass in the form of vapor and ice fragments (=short-period comet nuclei), whereas if M < or = 0.2 Moon, the body breaks up totally (the Main Belt asteroids origin approximately 3.9 Byr ago). 2H2 + O2 containing cometary nuclei are capable of burning or suffer new explosions when receiving an additional energy. The combustion in the sublimation products containing also light organics and 2H2 + O2 explains unexpected energetics and nearnuclear chemistry of Comet P/Halley (e.g. great abundances of negative and positive ions, atomic carbon, CO over CO2, origin of CHON particles etc) and its distant outbursts correlated, possibly, with the Solar activity. Thus the electrochemical processes in the dirty ice with organics, along with its subsequent thermal, radiative etc. processing, open up new potentials for explanation and prediction of quite unexpected discoveries.

Electric Conductivity↗
PubMed1996

Century scale solar variability imprinted in the 44Ti activity in meteorites.

The measurements of gamma-activity of the 44Ti (T1/2 = 66.6 years) produced by spallation reaction of galactic cosmic rays (GCR) in Alfianello, Olivenza, Rio Negro, Dhajala and Torino meteorites, which fell in the time interval 1883 AD (Alfianello)-1988 AD (Torino), show a century scale modulation, connected to long-term solar-wind flux variations in the interplanetary space. The variation of the 44Ti activity with the time of fall of meteorites is qualitatively consistent with the Gleissberg solar cycle, but the amplitude is three-four times higher than expected (about 5%) for GCR flux modulated by solar activity, as determined solely by the sunspot number. The cosmogenic 44Ti is a suitable radioisotope for this investigation, but its activity in meteorites is very low. We performed these measurements in the underground low level counting station of Monte dei Cappuccini in Torino, by means of a big hyperpure Ge crystal (approximately 2 kg) in selective coincidence with a heavy NaI (T1) scintillation detector (approximately 28 kg). This system allows a reliable and non destructive measurement of 44Ti (44Sc) in meteorites of 200-1200 g in weight. The background is about 1 count per day in the gamma-peak at 1157 keV of 44Sc in equilibrium with its parent 44Ti. The high stability of the performance allows long-lasting runs (approximately 10(7) s) in order to attain results with a standard deviation up to about 10%.

Cosmic Radiation↗
PubMed1996

Ablation and chemistry of meteoric materials in the atmosphere of Titan.

We compute the input of meteoric materials expected on Titan, and integrate this dust model with an ablation model and a comprehensive chemical model, investigating the effects on the atmosphere and surface. We find that a water deposition of approximately 10-100 times the expected interplanetary dust flux, or a recent large impact, is required to produce the observed CO2 abundance. Ionisation due to meteoric activity is not likely to be higher than that due to other sources.

Atmosphere↗
PubMedDate not supplied

Inquiring into indicators and origin of catastrophic events at stratigraphic boundaries.

Since 1982, numerous indicators of catastrophic events have been observed at the main stratigraphic boundaries in China during the Phanerozoic, i.e. Precambrian-Cambrian, Permian-Triassic, Cretaceous-Tertiary as well as Ordovician-Silurian and Devonian-Carboniferous boundaries. These markers are boundary clay layer, microspherules, high Ir anomaly, mass extinction of organisms and impact of meteorite. We support the hypothesis of the extraterrestrial origin of catastrophic events and suggest that the events at different stratigraphic boundaries might be different in features and processes.

Aluminum Silicates↗
PubMed1979

The effects of ultraviolet light on the degradation of organic compounds: a possible explanation for the absence of organic matter on Mars.

The analysis of the top layer of the Martian regolith at the two Viking landing sites did not reveal any indigenous organic compounds. However the existence of such compounds at deeper layers cannot be ruled out. Cosmochemical considerations indicate various potential sources for organic matter on Mars, such as comets and meteorites. Its disappearance from the top layer could be caused by degradation processes on the surface of the planet. Possible destructive agents include ultraviolet light, oxygen and metal oxides. In this study we tested the stability of a sample of the Murchison meteorite and various organic substances which have been detected in carbonaceous chondrites, such as glycine, adenine and naphthalene, to the action of ultraviolet light. The compounds were adsorbed on powdered quartz and on California desert soil and were irradiated in the presence or absence of oxygen. The organic content, before and after irradiation, was measured by carbon elementary analysis, UV-absorption, amino acid analysis or pyrolysis-gas chromatography-mass spectrometry. In the absence of oxygen, adenine and glycine appear to be stable over the given period of irradiation. A definite degradation was noticed in the case of naphthalene and the Murchison meteorite. In the presence of oxygen in amounts comparable to those on Mars all compounds were degraded. The degree of degradation was influenced by the irradiation time, temperature and oxygen content.

Adenine↗
PubMed1980

Organic compounds in meteorites.

Recent studies of carbonaceous chondrites provide evidence that certain organic compounds are indigenous and the result of an abiotic, chemical synthesis. The results of several investigators have established the presence of amino acids and precursors, mono- and dicarboxylic acids, N-heterocycles, and hydrocarbons as well as other compounds. For example, studies of the Murchison and Murray meteorites have revealed the presence of at least 40 amino acids with nearly equal abundances of D and L isomers. The population consists of both protein and non-protein amino acids including a wide variety of linear, cyclic, and polyfunctional types. Results show a trend of decreasing concentration with increasing carbon number, with the most abundant being glycine (41 n Moles/g). The monocarboxylic acids are more abundant (1.83 micro Moles propanoic acid/g Murchison), with hydrocarbons present in even greater abundance. In addition, quantification of the monocarboxylic acids shows a nearly equal distribution of straight and branched chain isomers. These and other results to be reviewed provide persuasive support for the theory of chemical evolution and provide the only natural evidence for the protobiological subset of molecules from which life on earth may have arisen.

Amino Acids↗
PubMed1980

The contribution of cometary volatiles to the primitive Earth.

It has been estimated that during its early history the Earth captured a mass of cometary material of the order of 10(23) grams. Since carbon is supposed to be at least three times more abundant in comets than in carbonaceous chondrites (3.5% C in C 1 chondrites), it can be deduced that about 1 x 10(22) grams of carbon (as carbon compounds), was added by comets to the surface of the prebiotic Earth. This carbon value is of the same order of magnitude as the value of the organic carbon buried in the Earth's sedimentary shell, but approximately one order of magnitude lower than the Earth's surface total carbon (7 x 10(22) gm). The capture of comets by the Earth would also have contributed to generating the appropriate aqueous and reducing environmental conditions necessary for organic synthesis. Although it is possible that some of the cometary carbon compounds falling on the Earth survived, most of them were probably decomposed by the heat and shock waves of the cometary collision. Upon quenching to low temperatures, however, the reactive chemical species produced by the impact would have recombined, leading to the synthesis of a great variety of organic molecules. Laboratory experiments with radiation, heat and shock waves have demonstrated that some of the synthesized compounds are biochemical molecules: amino acids, sugars, purines, and pyrimidines. These are essential to all living systems.

Carbon↗
PubMed2004

Impact-shocked rocks--insights into Archean and extraterrestrial microbial habitats (and sites for prebiotic chemistry?).

Impact-shocked gneiss shocked to greater than 10 GPa in the Haughton impact structure in the Canadian High Arctic has an approximately 25-times greater pore surface area than unshocked rocks. These pore spaces provide microhabitats for a diversity of heterotrophic microorganisms and in the near-surface environment of the rocks, where light levels are sufficient, cyanobacteria. Shocked rocks provide a moisture retaining, UV protected microenvironment. During the Archean, when impact fluxes were more than two orders of magnitude higher than today, the shocked-rock habitat was one of the most common terrestrial habitats and might have provided a UV-shielded refugium for primitive life. These potential habitats are in high abundance on Mars where impact crater habitats could have existed over geologic time periods of billions of years, suggesting that impact-shocked rocks are important sites to search for biomolecules in extraterrestrial life detection strategies. In addition to being favourable sites for life, during the prebiotic period of planetary history impact-shocked rocks might have acted as a site for the concentration of reactants for prebiotic syntheses.

Arctic Regions↗
PubMed2004

MEP (Mars Environment Package): toward a package for studying environmental conditions at the surface of Mars from future lander/rover missions.

In view to prepare Mars human exploration, it is necessary to promote and lead, at the international level, a highly interdisciplinary program, involving specialists of geochemistry, geophysics, atmospheric science, space weather, and biology. The goal of this program will be to elaborate concepts of individual instruments, then of integrated instrumental packages, able to collect exhaustive data sets of environmental parameters from future landers and rovers of Mars, and to favour the conditions of their implementation. Such a program is one of the most urgent need for preparing human exploration, in order to develop mitigation strategies aimed at ensuring the safety of human explorers, and minimizing risk for surface operations. A few main areas of investigation may be listed: particle and radiation environment, chemical composition of atmosphere, meteorology, chemical composition of dust, surface and subsurface material, water in the subsurface, physical properties of the soil, search for an hypothesized microbial activity, characterization of radio-electric properties of the Martian ionosphere. Scientists at the origin of the present paper, already involved at a high degree of responsibility in several Mars missions, and actively preparing in situ instrumentation for future landed platforms (Netlander--now cancelled, MSL-09), express their readiness to participate in both ESA/AURORA and NASA programs of Mars human exploration. They think that the formation of a Mars Environment working group at ESA, in the course of the AURORA definition phase, could act positively in favour of the program, by increasing its scientific cross-section and making it still more focused on human exploration.

Atmosphere↗
PubMed2004

Biological space experiments for the simulation of Martian conditions: UV radiation and Martian soil analogues.

The survivability of resistant terrestrial microbes, bacterial spores of Bacillus subtilis, was investigated in the BIOPAN facility of the European Space Agency onboard of Russian Earth-orbiting FOTON satellites (BIOPAN I -III missions). The spores were exposed to different subsets of the extreme environmental parameters in space (vacuum, extraterrestrial solar UV, shielding by protecting materials like artificial meteorites). The results of the three space experiments confirmed the deleterious effects of extraterrestrial solar UV radiation which, in contrast to the UV radiation reaching the surface of the Earth, also contains the very energy-rich, short wavelength UVB and UVC radiation. Thin layers of clay, rock or meteorite material were shown to be only successful in UV-shielding, if they are in direct contact with the spores. On Mars the UV radiation climate is similar to that of the early Earth before the development of a protective ozone layer in the atmosphere by the appearance of the first aerobic photosynthetic bacteria. The interference of Martian soil components and the intense and nearly unfiltered Martian solar UV radiation with spores of B. subtilis will be tested with a new BIOPAN experiment, MARSTOX. Different types of Mars soil analogues will be used to determine on one hand their potential toxicity alone or in combination with solar UV (phototoxicity) and on the other hand their UV protection capability. Two sets of samples will be placed under different cut-off filters used to simulate the UV radiation climate of Mars and Earth. After exposure in space the survival of and mutation induction in the spores will be analyzed at the DLR, together with parallel samples from the corresponding ground control experiment performed in the laboratory. This experiment will provide new insights into the principal limits of life and its adaptation to environmental extremes on Earth or other planets which and will also have implications for the potential for the evolution and distribution of life.

Bacillus subtilis↗
PubMed2005

Screening of organic halogens and identification of chlorinated benzoic acids in carbonaceous meteorites.

The occurrence of halogenated organic compounds measured as a sum parameter and the evidence of chlorinated benzoic acids in four carbonaceous meteorites (Cold Bokkeveld, Murray, Murchison and Orgueil) from four independent fall events is reported. After AOX (Adsorbable organic halogen) and EOX (Extractable organic halogen) screening to quantify organically bound halogens, chlorinated organic compounds were analyzed by gas chromatography. AOX concentrations varying from 124 to 209 microg Cl/g d.w. were observed in carbonaceous meteorites. Ion chromatographic analysis of the distribution of organically bound halogens performed on the Cold Bokkeveld meteorite revealed that chlorinated and brominated organic compounds were extractable, up to 70%, whereas only trace amounts of organofluorines could be extracted. Chlorinated benzoic acids have been identified in carbonaceous meteorite extracts. Their presence and concentrations raise the question concerning the origin of halogenated, especially chlorinated, organic compounds in primitive planetary matter.

Carbon↗
PubMed2006

Performances under representative pressure and temperature conditions of the gas chromatography-mass spectrometry space experiment to investigate Titan's atmospheric composition.

In the frame of the calibration of the aerosol collector and pyrolyser, and gas chromatography-mass spectrometry experiments of the Huygens probe arrived at Titan, systematic experimental studies were led to estimate the influence of the operating conditions on the analyses that should have been achieved in the Titan's atmosphere. The primary objective of this study was to estimate the influence of operating conditions variations induced by (i) instrumental modifications made shortly before the probe launch which can have changed the operating pressures; (ii) the change of the probe environmental conditions (pressure, temperature) during its descent in the atmosphere; (iii) a possible deviation of pressure and temperature regulations from their nominal values because of the long journey of the instrument in space, or of other external events. The secondary objective of this work was to create an analytical database that can be used as a reference to treat the chromatograms obtained in situ, and help to identify chromatographically the analyzed species, complementary to mass spectrometry. Beyond the application to a specific instrument, this work was also useful to experimentally estimate the fundamental evolution of the separation as a function of the changes of operating conditions with time. The obtained results show (i) the significant influence of inlet and outlet pressure variation on the time of analysis, but not on the separation power. It thus enables to significantly shorten the analysis duration, and thus to analyze more compounds within the fixed time of analysis of the instrument; (ii) the significant influence of temperature on the retention. In this frame, the enthalpies of exchange between the gas phase and the stationary phase of the species were determined to be used to retrieve the analyzed species in case of deviation of the operating temperature; (iii) that the possible aging of the columns does not have influence on the columns efficiency and separation power; (iv) the analytical capabilities of the gas chromatography-mass spectrometry experiment within operating conditions representative of those encountered in situ. Finally, in spite of possible operating condition changes, it is shown that results coming from the gas chromatograph-mass spectrometer experiment, which are currently under analysis, could bring important information on the Titan's atmosphere and its history.

Atmosphere↗
PubMed2004

The universe: a cryogenic habitat for microbial life.

Panspermia, an ancient idea, posits that microbial life is ubiquitous in the Universe. After several decades of almost irrational rejection, panspermia is at last coming to be regarded as a serious contender for the beginnings of life on our planet. Astronomical data is shown to be consistent with the widespread distribution of complex organic molecules and dust particles that may have a biological provenance. A minuscule (10(-21)) survival rate of freeze-dried bacteria in space is all that is needed to ensure the continual re-cycling of cosmic microbial life in the galaxy. Evidence that terrestrial life may have come from elsewhere in the solar system has accumulated over the past decade. Mars is seen by some as a possible source of terrestrial life, but some hundreds of billions of comets that enveloped the entire solar system, are a far more likely primordial reservoir of life. Comets would then have seeded Earth, Mars, and indeed all other habitable planetary bodies in the inner regions of the solar system. The implications of this point of view, which was developed in conjunction with the late Sir Fred Hoyle since the 1970s, are now becoming amenable to direct empirical test by studies of pristine organic material in the stratosphere. The ancient theory of panspermia may be on the verge of vindication, in which case the entire universe would be a grand crucible of cryomicrobiology.

Astronomical Phenomena↗
PubMed2005

Caroline Herschel: 'the unquiet heart'.

Caroline Herschel was famous in her own time as the discoverer of eight comets, but of even greater significance was the help she gave her brother William in his exploration of 'the construction of the heavens'. She acted as his amanuensis during night watches, wrote up neat copies of their observing records and prepared his papers for publication. She also compiled an index to John Flamsteed's Star Catalogue, which was published by the Royal Society at its own expense, and after William's death she reorganized his catalogues of nebulae so that his son John could revise his father's work. Yet Caroline's was a hard and largely loveless life, for which she found the recognition that came her way a scant consolation.

Abstracting and Indexing↗
PubMed2004

Search for EPR markers of the history and origin of the insoluble organic matter in extraterrestrial and terrestrial rocks.

The insoluble organic matter (IOM) of three carbonaceous meteorites (Orgueil, Murchison and Tagish Lake meteorites) and three samples of cherts (microcrystalline SiO2 rock) containing microfossils with age ranging between 45 million years and 3.5 billion years is studied by electron paramagnetic resonance (EPR). The age of the meteorites is that of the solar system (4.6 billion years). The purpose of this work was to determine the EPR parameters, which allow us to discriminate between biogenic and extra terrestrial origin for the organic matter. Such indicators should be relevant for the controversy regarding the biogenicity of the organic matter in the oldest cheroot (3.5 billion years) and in Martian meteorites containing microbe-like microstructures. The organic matter of meteorites contains a high concentration of diradicaloid moieties characterised by a diamagnetic ground state S = 0 and a thermally accessible triplet state S = 1. The three meteorites exhibit the same singlet-triplet gap (ST gap) DeltaE approximately 0.1 eV. To the best of our knowledge, such diradicaloids are unknown in insoluble organic matter of terrestrial origin. We have also shown that the EPR linewidth of insoluble organic matter in cherts and coals decrease logarithmically with the age of the organic matter. We conclude from this result that the organic matter in the oldest cherts (3.5 billion years) has the same age as their SiO2 matrix, and is not due to a latter contamination by bacteria, as was recently found in meteoritic samples.

Carbon↗
PubMed2005

The micro-distribution of carbonaceous matter in the Murchison meteorite as investigated by Raman imaging.

The carbonaceous Murchison chondrite is one of the most studied meteorites. It is considered to be an astrobiology standard for detection of extraterrestrial organic matter. Considerable work has been done to resolve the elemental composition of this meteorite. Raman spectroscopy is a very suitable technique for non-destructive rapid in situ analyses to establish the spatial distribution of carbonaceous matter. This report demonstrates that Raman cartography at a resolution of 1 microm2 can be performed. Two-dimensional distribution of graphitised carbon, amorphous carbonaceous matter and minerals were obtained on 100 microm2 maps. Maps of the surface of native stones and of a powdered sample are compared. Graphitic and amorphous carbonaceous domains are found to be highly overlapping in all tested areas at the surface of the meteorite and in its interior as well. Pyroxene, olivine and iron oxide grains are embedded into this mixed carbonaceous material. The results show that every mineral grain with a size of less than a few microm2 is encased in a thin carbonaceous matrix, which accounts for only 2.5 wt.%. This interstitial matter sticks together isolated mineral crystallites or concretions, including only very few individualized graphitised grains. Grinding separates the mineral particles but most of them retain their carbonaceous coating. This Raman study complements recent findings deduced from other spatial analyses performed by microprobe laser-desorption laser-ionisation mass spectrometry (microL2MS), transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).

Carbon↗