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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Evidence for chemical processing of precometary icy grains in circumstellar environments of pre-main-sequence stars

We report the detection of a broad absorption feature near 2166/cm in the spectrum of the Taurus cloud cource Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166/cm absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C triple bonded to N containing compound (called X(C triple bonded to N)) that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components. We find a nonlinear anticorrelation between the abundance of X(C triple bonded to N) and frozen CO components in nonpolar lattices. We find no correlation between the abundance of X(C triple bonded to N) and frozen CO in polar lattices. Because the abundances of frozen CO and H2O are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C triple bonded to N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main-sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

Tegler, Stephen C.↗
NASA NTRS1996

Toward an Astrophysical Theory of Chondrites

Sunlike stars are born with disks. Based on our recently developed model to understand how a magnetized new star interacts with its surrounding accretion disk, we advanced an astrophysical theory for the early solar system. The aerodynamic drag of a magnetocentrifugally driven wind out of the inner edge of a shaded disk could expose solid bodies lifted into the heat of direct sunlight, when material is still accreting onto the protosun. Chondrules, calcium-aluminum-rich inclusions (CAI's), and rims could form along the flight for typical self-consistent parameters of the outflow in different stages of star formation. The process gives a natural sorting mechanism that explains the size distribution of CAI's and chondrules, as well as their associated rims. Chondritic bodies then subsequently form by compaction of the processed solids with the ambient nebular dust comprising the matrices after their reentry at great distances from the original launch radius.

Shang, Hsien↗
NASA NTRS1996

The Mass of Large Impactors

By means of a simplified dynamical model, we have computed the eccentricity change in the orbit of each giant planet, caused by a single, large impact at the end of the accretion process. In order to set an upper bound on this eccentricity change, we have considered the giant planets' present eccentricities as primordial ones. By means of this procedure, we were able to obtain an implicit relation for the impactor masses and maximum velocities. We have estimated by this method the maximum allowed mass to impact Jupiter to be approx. 1.136 x 10(exp -1), being in the case of Neptune approx. 3.99 x 10(exp -2) (expressed in units of each planet final mass). Due to the similar present eccentricities of Saturn, Uranus and Jupiter, the constraint masses and velocities of the bodies to impact them (in units of each planet final mass and velocity respectively) are almost the same for the three planets. These results are in good agreement with those obtained by Lissauer and Safronov. These bounds might be used to derive the mass distribution of planetesimals in the early solar system.

Parisi, M. G.↗
NASA NTRS1995

X-Ray Emission from the Sun in Its Youth and Old Age

We have obtained ROSAT PSPC (Roentgen Satellite Position Sensitive Proportional Counter) pointed observations of two nearby G stars of ages 70 Myr and 9.5 Gyr that are of unique importance as proxies for the Sun at the two extremes of its main-sequence evolutionary lifetime. The younger star, HD 129333 (EK Dra; G0 V), a rapid rotator with a 2.7 day period, is a strong source with an X-ray luminosity L(x)(0.2-2.4 keV) = (7.5-11.5) x 10(exp 29) erg/s. Modeling suggests a two-temperature corona with T(1) = (2.0 +/- 0.3) x 10(exp 6) K and T(2) = (9.7 +/- 0.3) x 10(exp 6) K (formal uncertainties). A continuous emission measure distribution, increasing to higher temperatures and with a cutoff at (20-30) x 10(exp 6) K, yields even better fits to the data. The old star, beta Hyi (HR 98; G2 IV), represents the Sun in the future, near the end of its hydrogen-core burning stage, when it should be rotating more slowly (present P(rot) = 25.4 day) and should have lower levels of activity. The ROSAT measurements yield L(x) = (0.9-3.0) x 10(exp 27) ergs/s and a rather cool, single coronal temperature of T = (1.7 +/- 0.4) x 10(exp 6) K. For comparison, the Sun has L(x) approx. equal to 2 x 10(exp 27) ergs/s and a coronal temperature of about T = 2 x 10(exp 6) K. These stars provide information on the decline of the stellar (and specifically solar) magnetic activity from extreme youth to old age. HD 129333 is also important in that it yields an estimate of the solar soft X-ray flux in the early solar system at the epoch of the terminal stages of planetary accretion.

Dorren, J. D.↗
NASA NTRS1997

Observations and Modeling of the Transient General Circulation of the North Pacific Basin

The objective of this study was to clarify the role that interstellar-cloud chemistry played in forming the population of organic molecules presently found in carbonaceous meteorites. This goal was to be achieved by means of defining the isotopic components present in organic and related phases in the meteorites and thereby identify the processes and source reservoirs involved in organic synthesis in the early solar system. Isotopic analysis of separated amino acids from the Murchison meteorite yielded results that are complex and not fully interpretable at this time. Substantial inter-acid variability in D/H ratio was observed, some but not all of which could be attributed to exchange with terrestrial hydrogen. Pronounced, though smaller, variability was also found for N-15/N-14 ratios. For both D/H and N-15/N-14 data, observed meteoritic values were substantially greater than found in terrestrial materials, providing a robust constraint on degrees of possible terrestrial contamination. Also, C-13/C-12 ratios, though falling within the range of data found on earth, significantly exceeded those characteristic of naturally occurring terrestrial amino acids. Inter-acid variability in C-13/C-12 ratios was muted relative to that observed for D/H and N-15/N-14 but still lay well outside of experimental uncertainty. No systematic relationship could be observed between variations in H, C and N isotopes. Two anomalous components were also found during the course of this study. A highly (greater than 6% relative to terrestrial) N-15-depleted, N-rich compound, which has not yet been identified, co-eluted with some amino acids. Clearly the Murchison meteorite sampled nitrogen from a number of highly diverse isotopic reservoirs. In fact, from this and related studies, it is now apparent that the distribution of nitrogen isotopes in the primitive solar system was extremely inhomogeneous. The second anomalous result obtained in the present study was for an extract of 'ammonia' from Murchison. It should be noted that this sample consisted of ammonia that was probably derived from a number of different compounds present in the meteorite itself, possibly including amines and amides, as well as ammonia sensu strictu and ammonium slats. However, the significance of this analysis is that the N-15/N-14 ratio measured was much lower than those found for the meteoritic amino acids (+2% vs around + 9% relative to terrestrial). This raises an important question concerning the source of the ammonia that was involved in synthesis of the amino acids. This issue needs to be explored further.

Kerridge, John F.↗
NASA NTRS1997

Lyman Alpha Photochemistry in the Solar Nebula

The purpose of the project "Lyman Alpha Photochemistry in the Solar Nebula" was to model photochemistry in the primitive solar nebula and the early solar systems. As part of the modeling, it was necessary to model the composition of the gas and dust accreted by the solar nebula. This final report contains a list of publications where the results of this project have been published.

Fegley, Bruce, Jr.↗
NASA NTRS1998

Development of a High Resolution-High Sensitivity Ion Microprobe Facility for Cosmochemical Applications

NASA NAGW-4112 has supported development of the CAMECA ims 1270 ion microprobe at UCLA for applications in cosmochemistry. The instrument has been brought to an operational status and techniques developed for accurate, precise microbeam analysis of oxygen isotope ratios in polished thin-sections. We made the first oxygen isotopic (delta(18)O and delta(17)O) measurements of rare mafic silicates in the most chemically primitive meteorites, the a chondrites (Leshin et al., 1997). The results have implications for both high temperature processing in the nebula and low-T aqueous alteration on the CI asteroid. We have performed measurements of oxygen isotopic compositions of magnetite and co-existing olivine from carbonaceous (Choi et al., 1997) and unequilibrated ordinary chondrites (Choi et al., in press). This work has identified a significant new oxygen isotope reservoir in the early solar system: water characterized by a very high Delta(17)) value of approx. 5 % per thousand. We have determined the spatial distributions of oxygen isotopic anomalies in all major mineral phases of a type B CAI from Allende. We have also studied an unusual fractionated CAI from Leoville and made the first oxygen isotopic measurements in rare CAIs from ordinary chondrites.

McKeegan, Kevin D.↗
NASA NTRS1995

Evidence for Chemical Processing of Precometary Icy Grains In Circumstellar Environments of Pre-Main-Sequence Stars

We report the detection of a broad absorption feature near 2166 cm-1 in the spectrum of the Taurus cloud source Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166 cm-1 absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C=-N containing compound [called X(C=-N)] that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components, We find a nonlinear anticorrelation between the abundance of X(C=-N) and frozen CO in non- polar lattices. We find no correlation between the abundance of X(C=-N) and frozen CO in polar lattices. Because the abundances of frozen CO and H20 are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C=-N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main- sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

Teglier, Stephen C.↗
NASA NTRS2000

Preliminary Examination of Sahara 99555: Mineralogy and Experimental Studies of a New Angrite

A 2710 g meteorite, Sahara 99555 (Sah99), was recently recovered from the Sahara and reported to be the 5th angrite. It is the largest angrite ever found and may offer useful information to better understand the unusual petrogeneses of this rare achondrite group. It may also allow us to examine the chronological record of igneous activity in the very early solar system. We obtained a 2.6 g chip of Sah99 and here present a preliminary report of its petrology and mineralogy in conjunction with a crystallization experiment on an analogue composition.

Mikouchi, T.↗
NASA NTRS1999

Synthesis of Large Molecules in Cometary Ice Analogs: Physical Properties Related to Self-Assembly Processes

The combination of realistic laboratory simulations and infrared observations have revolutionized our understanding of interstellar dust and ice-the main component of comets. Since comets and carbonaceous micrometeorites may have been important sources of volatiles and carbon compounds on the early Earth, their organic composition may be related to the origin of life. Ices on grains in molecular clouds contain a variety of simple molecules. The D/H ratios of the comets Hale-Bopp and Hyakutake are consistent with a primarily interstellar ice mixture. Within the cloud and especially in the presolar nebula through the early solar system, these icy grains would have been photoprocessed by the ultraviolet producing more complex species such as hexamethylenetetramine, polyoxymethylenes, and simple keones. We reported at the 1999 Bioastronomy meeting laboratory simulations studied to identify the types of molecules which could have been generated in pre-cometary ices. Experiments were conducted by forming a realistic interstellar mixed-molecular ice (H2O, CH3OH, NH3 and CO) at approximately 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The gas mixture was typically 100:50:1:1, however when different ratios were used material with similar characteristics was still produced. The residue that remained after warming to room temperature was analyzed by HPLC, and by several mass spectrometric methods. This material contains a rich mixture of complex compounds with mass spectral profiles resembling those found in IDPs and meteorites. Surface tension measurements show that an amphiphilic component is also present. These species do not appear in various controls or in unphotolyzed samples. Residues from the simulations were also dispersed in aqueous media for microscopy. The organic material forms 10-40 gm diameter droplets that fluoresce at 300-450 nm under UV excitation. These droplets have a morphology and internal structure which appear strikingly similar to those produced by extracts of the Murchison meteorite. Together, these results suggest a link between organic material photochemically synthesized on the cold grains in dense, interstellar molecular clouds and compounds that may have contributed to the organic inventory of the primitive Earth. For example, the amphiphilic properties of such compounds permit self-assembly into the membranous boundary structures that required for the first forms of cellular life.

Dworkin, Jason P.↗
NASA NTRS2001

In Situ Measurements of Meteoric Ions

Metal ions found in the atmosphere above 60 km are the result of incoming meteoroid atmospheric ablation. Layers of metal ions are detected by sounding rocket in situ mass spectrometric sampling in the 80 to 130 km region, which coincides with the altitude region where meteors are observed. Enhancements of metal ion concentrations occur during meteor showers. Even outside of shower periods, the metal ion altitude profiles vary from measurement to measurement. Double layers are frequent at middle latitudes. More than 40 different meteoric atomic and molecular ions, including isotopes, have been detected. Atmospheric metal ions on average have an abundance that matches chrondritic material, the same composition as the early solar system. However there are frequently local departures from this composition due to differential ablation, species dependent chemistry and mass dependent ion transport. Metal ions react with atmospheric O2, O, O3, H2O and H2O2 to form oxygenated and hydrogenated ionic compounds. Metal atomic ions at high altitudes have long lifetimes. As a result, these ions, in the presence of Earth's magnetic field, are transported over long distances by upper atmospheric winds and ionospheric electric fields. Satellite measurements have detected metal ions as high as, approximately 1000 km and have revealed circulation of the ions on a global scale.

Grebowsky, Joseph M.↗
NASA NTRS2001

Development And Application Of The Ion Microprobe For Analysis Of Extraterrestrial Materials

This report covers the work carried out under NASA Grant NAG5-4083. The research was directed toward analyses of early solar system material, of presolar grains preserved in meteorites, and toward theoretical studies of nucleosynthesis in stars related to the chemical evolution of the galaxy and the formation of the solar system. The work was carried out over the time period 15 February 1998 - 31 May 2001 and involved the participation of the following individuals: M. Busso, Visiting Associate, Professor of Astrophysics, Perugia University, Italy; B.-G. Choi, research fellow, now Associate Professor at Seoul National University, Korea; H. C. Connolly, research fellow, now at Kingsborough Community College, CUNY; R. Gallino, Visiting Associate, Professor of Astrophysics, University of Torino; Y. Guan, Smithsonian Institution; C. Hohenberg, Professor of Physics, Washington University, St. Louis; M. Heinrich, electronics and systems engineer, Caltech; W. Hsu, research fellow, Caltech; T. LaTourrette, research fellow, now at Rand Corporation; G. R. Huss, Senior Research Scientist, now at Arizona State University; N. Krestina, research fellow in geochemistry, Caltech; G. J. MacPherson, Smithsonian Institution; K. Nollett, research fellow in astrophysics; Y.-Z. Qian, Professor of Physics, University of Minnesota; G. Srinivasan, research fellow, now Research Scientist, Physical Research Laboratory, Ahmedabad, India.

Wasserburg, G. J.↗
NASA NTRS2003

I-Xe Ages and Trapped Xe Compositions

I-Xe isochrons are mixing lines between a single trapped and a single iodine derived component. The slope of this line establishes initial iodine and hence the I-Xe age. One end of the isochron is fixed by the composition of the trapped Xe component, which should be representative of the Xe that was present in the early solar system (Q-Xe or OC-Xe). Because the I/Xe ratio in the solar nebular was ~1, and the I-129/I-127 was about 10-4, the Xe-129 in trapped Xe cannot evolve appreciably with decay of I-129. While it may be possible for Xe in a closed system with elevated I/Xe ratios to evolve producing trapped components with higher Xe-129/Xe-132 ratios, trapped Xe compositions with lower (sub-planetary) Xe-129/Xe-132 ratios seem implausible.

Hohenberg, C. M.↗
NASA NTRS2003

Mineralogy and Textural Characteristics of Fine-grained Rims in the Yamato 791198 CM2 Carbonaceous Chondrite: Constraints on the Location of Aqueous Alteration

Carbonaceous chondrites provide important clues into the nature of physical and chemical processes in the early solar system. A question of key importance concerns the role of water in solar nebular and asteroidal processes. The effects of water on primary mineral assemblages have been widely recognized in chondritic meteorites, especially the CI and CM carbonaceous chondrites. These meteorites have undergone extensive aqueous alteration that occurred prior to their arrival on Earth. In the case of the CM chondrites, this alteration has resulted in the partial to complete replacement of the primary nebular phases with secondary alteration phases. Considerable controversy exists as to the exact location where the alteration of the CM chondrites occurred. Several textural lines of evidence have been cited in support of aqueous alteration prior to the accretion of the final parent asteroid. An important line of evidence to support this hypothesis is the dis-equilibrium nature of fine-grained rims and matrix materials. [2] also noted the juxtaposition of micron-sized Fe-Ni metal grains and apparently unaltered chondrule glass against hydrated rim silicates. Conversely, there is a large body of evidence in favor of parent body alteration such as the occurrence of undisturbed Fe-rich aureoles and the systematic redistribution of elemental components over millimeters, e.g., Mg(+2) into the matrix and Fe(+2) into chondrules etc.

Chizmadia, Lysa J.↗
NASA NTRS2003

Molecular and Enantiomeric Analysis of Organic Compounds in Carbonaceous Meteorites

Carbonaceous meteorites are relatively enriched in carbon. Much of this carbon is in the form of soluble organic compounds. The Murchison and Murray meteorites are the best-characterized carbonaceous meteorites with respect to organic chemistry. Their content of organic compounds has led to an initial understanding of early solar system organic chemistry as well as what compounds may have played a role in the origin of life (Cronin and Chang, 1993). Reported compounds include: amino acids, amides, carboxylic acids, sulfonic acids, and polyols. This talk will focus on the molecular and enantiomeric analysis of individual meteoritic compounds: polyol acids; and a newly identified class of meteorite compounds, keto acids, i.e., acetoacetic acid, levulinic acid, etc. Keto acids (including pyruvic) are critically important in all contemporary organisms. They are key intermediates in metabolism and processes such as the citric acid cycle. Using gas chromatography-mass spectrometry we identified individual meteoritic keto acids after derivatization to one or more of the following forms: isopropyl ester (ISP), trimethyIsiIy1 (TMS), tert-butyldimethylsilyl (BDMS). Ongoing analyses will determine if, in addition to certain amino acids from Murchison (Cronin and Pizzarello, 1997), other potentially important prebiotic compounds also contain enantiomeric excesses, i.e., excesses that could have contributed to the current homochirality of life.

Cooper, George↗
NASA NTRS2004

Aqueous Alteration of Carbonaceous Chondrites: New Insights from Comparative Studies of Two Unbrecciated CM2 Chondrites, Y 791198 and ALH 81002

Carbonaceous chondrites are an important resource for understanding the physical and chemical conditions in the early solar system. In particular, a long-standing question concerns the role of water in the cosmochemical evolution of carbonaceous chondrites. It is well established that extensive hydration of primary nebular phases occurred in the CM and CI chondrites, but the location where this alteration occurred remains controversial. In the CM2 chondrites, hydration formed secondary phases such as serpentine, tochilinite, pentlandite, carbonate and PCP. There are several textural observations which suggest that alteration occurred before the accretion of the final CM parent asteroid, i.e. preaccretionary alteration. Conversely, there is a significant body of evidence that supports parent-body alteration. In order to test these two competing hypotheses further, we studied two CM chondrites, Y-791198 and ALH81002, two meteorites that exhibit widely differing degrees of aqueous alteration. In addition, both meteorites have primary accretionary textures, i.e. experienced minimal asteroidal brecciation. Brecciation significantly complicates the task of unraveling alteration histories, mixing components that have been altered to different degrees from different locations on the same asteroidal parent body. Alteration in Y-791198 is mostly confined to chondrule mesostases, FeNi metal and fine-grained matrix and rims. In comparison, the primary chondrule silicates in ALH81002 have undergone extensive replacement by secondary hydrous phases. This study focuses on compositional and textural relationships between chondrule mesostasis and the associated rim materials. Our hypothesis is: both these components are highly susceptible to aqueous alteration and should be sensitive recorders of the alteration process. For parent body alteration, we expect systematic coupled mineralogical and compositional changes in rims and altered mesostasis, as elemental exchange between these components occurs. Conversely, for preaccretionary alteration, there should be no clear relationships between the rims and mesostases.

Chizmadia, L. J.↗
NASA NTRS2004

Evidence for Live Cl-36 in Ca-Al-rich Inclusions from the Ningqiang Carbonaceous Chondrite

The short-lived radionuclide Cl-36 decays to either Ar-36 (98.1%, beta(sup -)) or S-36 (1.9%, epsilon and beta(sup +)), with a half life of 3.01 x 10(exp 5) yr. Both the nucleosynthetic and spallation models suggest high initial Cl-36/Cl-35 ratios ((Cl-36/Cl-35)o up to approximately 10(exp -4)) in the early solar system. Previous observed excess Ar-36 in Efremovka matrix has been interpreted to represent a much lower (Cl-36/Cl-35)o ratio of approximately 1 x 10(exp -6). From the observed S-36 excesses in sodalite in calcium aluminum-rich inclusions (CAIs), we report in this study the first direct evidence of the presence of Cl-36 in primitive meteorites. The inferred (Cl-36/Cl-35)o ratios range from approximately 5 x 10(exp -6) to approximately 1 x 10(exp -5).

Lin, Y.↗
NASA NTRS2004

On the Origin of GEMS

GEMS (glass with embedded metal and sulfides) are a major component of anhydrous interplanetary dust particles (IDPs) their physical and chemical characteristics show marked similarities to contemporary interstellar dust. Recent oxygen isotopic measurements confirm that at least a small fraction (less than 5%) of GEMS are demonstrably presolar, while the remainder have ratios that are indistinguishable from solar values. GEMS with solar oxygen isotopic compositions either (1) had their isotopic compositions homogenized through processing in the interstellar medium (ISM), or (2) formed in the early solar system. Isotopic homogenization necessarily implies chemical homogenization, so (interstellar) GEMS compositions should reflect the average composition of dust in the local ISM. We performed a systematic examination of the bulk chemistry of GEMS in primitive IDPs in order to test this hypothesis.

Keller, L. P.↗