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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Proton-associated alpha-irradiation in the early solar system - A possible K-41 anomaly

It is shown that alpha-particle fluences associated with proton fluences sufficiently high to produce the Al-correlated excess of Mg-26 found in the Allende meteorite produce equally significant amounts of Ca-41. The Ca-41 is produced by Ar-38(alpha,n)Ca-41 reactions occurring in the gas and condenses into the Ca-Al-rich grains forming at that time. After the decay of Ca-41, these grains will have a Ca-correlated excess of K-41. The question is considered whether the proposed scheme is capable of producing an observable excess of K-41. A calculation is conducted of the magnitude of the K-41 excess expected to be found in Ca-Al-rich grains for various ratios of Ca/K by developing an irradiation-condensation model. It is shown that on the basis of the currently available data it is not possible to come to firm conclusions regarding the validity of the irradiation model.

Dwek, E.↗
NASA NTRS1978

Precondensed matter - Key to the early solar system

Explicit astrophysical details are developed for the hypothesis that chemical and isotopic anomalies in primitive solar-system samples reflect routine initial chemical conditions within precondensed matter. The central feature of this theory concerns the chemical state of presolar dust, which is regarded as never having been vaporized in the region where the most chemically primitive samples (carbonaceous meteorites) accumulated. It is suggested that the initial chemical state of heavy atoms during meteorite and planetary accumulation was distributed between a refractory-mineral component from high-temperature condensation and a volatile component resulting from cold matter adhering to preexisting grains. Thermal conditions in the solar nebula are considered along with the existence of supernova condensates and other thermal condensates in the interstellar dust. Fractionation into volatile and refractory elements is idealized in terms of four distinct interstellar components, and the fractionated precondensed matter is described.

Clayton, D. D.↗
NASA NTRS1978

Evidence for the existence of Pd-107 in the early solar system

Measurements of the concentration and isotopic composition of Ag and Pd in the Santa Clara iron meteorite suggest that in situ decay of Pd-107 occurred in the meteorite or its parent body. The initial solar ratio of Pd-107/Pd-110 is estimated from the observed ratio of excess Ag-107/Pd-110, and the value of the Pd ratio is incompatible with an interval of approximately 100,000,000 years between the end of nucleosynthesis and the formation of planetary objects but is compatible with a later injection of material. The inferred existence of Pd-107 and Al-26 indicates that the late injection included freshly synthesized material of both intermediate and low atomic weight on a similar time scale. The significance of the Pd-107/Ag-107 chronometer is considered.

Kelly, W. R.↗
NASA NTRS1979

Electromagnetic heating of minor planets in the early solar system

Electromagnetic processes occurring in the primordial solar system are likely to have significantly affected planetary evolution. In particular, electrical coupling of the kinetic energy of a dense T-Tauri-like solar wind into the interior of the smaller planets could have been a major driver of thermal metamorphism. Accordingly a grid of asteroid models of various sizes and solar distances was constructed using dc transverse magnetic induction theory. Plausible parameterizations with no requirement for a high environmental temperature led to complete melting for Vesta with no melting for Pallas and Ceres. High temperatures were reached in the Pallas model, perhaps implying nonmelting thermal metamorphosis as a cause of its anomalous spectrum. A reversal of this temperature sequence seems implausible, suggesting that the Ceres-Pallas-Vesta dichotomy is a natural outcome of the induction mechanism. Highly localized heating is expected to arise due to an instability in the temperature-controlled current distribution. Localized metamorphosis resulting from this effect may be relevant to the production and evolution of pallasites, the large presumed metal component of S object spectra, and the formation of the lunar magma ocean.

Herbert, F.↗
NASA NTRS1979

Lunar and Planetary Science Conference, 10th, Houston, Tex., March 19-23, 1979, Proceedings. Volume 2 - Early solar system and lunar regolith

Papers are presented concerning studies of the lunar regolith, the remote sensing of the surface compositions of the moon and planets, and the origin and evolution of the solar system. Specific topics include the stratigraphy and depositional history of the Apollo 17 deep drill core, the trace element and metallic iron abundances in fractions of the Apollo 15 deep drill core, the surface chemistry of lunar impact glasses, cosmic ray-produced noble gases in lunar samples, and the properties of microcraters and cosmic dust less than 1000 A in diameter. Attention is also given to the remote sensing of mare surface titanium concentrations, Viking Lander multispectral images, star and planetary system formation in collapsing, viscous, rotating clouds and the importance of planet size to basaltic volcanism.

Merrill, R. B.↗
NASA NTRS1982

X-ray emission from young stars and implications for the early solar system

Recent observations of soft X-ray emission from solar-type stars obtained with the Einstein X-Ray Observatory indicate that X-ray luminosity is inversely correlated with stellar age. If this result is applied to the sun and if X-ray emission is a valid indicator of other manifestations of solar activity, then past solar wind and flare levels can be inferred. It can qualitatively explain the excess xenon and nitrogen found in the lunar regolith compared to the level expected from the contemporary solar wind. X-ray emission from T Tauri and other low-mass pre-main-sequence stars is both highly luminous and variable, indicating the presence of flares approximately 4000 times stronger than the largest flares seen in the contemporary sun. The proton flux from such solar flares during the one to ten million-year pre-main-sequence phase would be sufficient to account for the Al-26 anomaly in meteorites.

Feigelson, E. D.↗
NASA NTRS1984

Early solar system aqueous activity - Sr isotope evidence from the Orgueil CI meteorite

The Sr isotopic composition and Rb-87/Sr-86 ratio have been measured in carbonates and sulfate separated from the Orgueil meteorite in order to determine the time when liquid water may have acted on the parent body. Both of the studied phases probably precipitated from aqueous solution. The results show that carbonate deposition occurred contemporaneously with parent body formation or shortly after it, probably within 100 Myr. On the other hand, at least some of the calcium sulfate seems to have been formed recently.

Macdougall, J. D.↗
NASA NTRS1987

Experimental constraints on heating and cooling rates of refractory inclusions in the early solar system

The refractory inclusions in carbonaceous chondrites were the subject of considerable interest since their discovery. These inclusions contain minerals that are predicted to be some of the earliest condensates from the solar nebula, and contain a plethora of isotopic anomalies of unknown origin. Of particular interest are those coarse-grained inclusions that contain refractory metal particles (Fe, Ni, Pt, Ru, Os Ir). Experimental studies of these inclusions in terrestrial laboratories are, however, complicated because the dense particles tend to settle out of a molten or partially molten silicate material. Heating experiments in the Space Station technology and microgravity in order to observe the effects of metal nuggets (which may act as heterogeneous nucleation sites) on nucleation rates in silicate systems and to measure simultaneously the relative volatilization rate of siderophile and lithophile species. Neither experiment is possible in the terrestrial environment.

Boynton, W. V.↗
NASA NTRS1993

On high-temperature formation of iron-rich olivine in the early solar system

A kinetic restriction on the formation of fayalite-rich olivine in equilibrium with the cooling solar-composition gas appears to exist at the low temperature of approximately 500 K. We offer a high-temperature formation mechanism (different from simple condensation) which operates at high hydrogen depletion (up to 300 times) relative to solar abundance. We show how the necessary depletion rate decreases with temperature (thermodynamical equilibrium is suggested). The consequences for planet formation are considered.

Dorofeyeva, V. A.↗
NASA NTRS1993

Recondensation in the early solar system: Physical conditions and source material

Many physical processes in the solar nebula led to fractionation of the gaseous phase of the preplanetary material. Some of these processes are listed with corresponding type of fractionation in terms of Rock/Ice/Gas. Recondensation from fractionated gas phase yields different compositions of condensates. In some detail, one type of fractionation is considered: impact heating with evaporation and subsequent recondensation of material during intercollisions of planetesimals. For thermodynamical simulation of recondensation in such a process one needs (1) P-T parameters and (2) some initial source material to be heated, evaporated, and recondensed. These two problems are addressed.

Vityazev, A. V.↗
NASA NTRS1994

Non-equilibrium chemistry of the early solar system

This final report contains a list of publications supported in whole or part by NAG9-108 in the time period 1 May 1985 to 30 April 1994. Also contained is a list of invited papers with abstracts supported in whole or part by this grant in the same time period. A copy of the 1993 paper by Ronald G. Prinn, 'Protostars and Planets III', is attached since it had not previously been sent to NASA.

Prinn, Ronald G.↗
NASA NTRS1994

What does the fine-scale petrography of IDPs reveal about grain formation and evolution in the early solar system?

The 'pyroxene' interplanetary dust particles (IDP's) may be the best samples for investigation of primordial grain-forming reactions because they appear to have experienced negligible post-accretional alteration. They are likely to continue to yield information about gas-to-solid condensation and other grain-forming reactions that may have occurred either in the solar nebular or presolar interstellar environments. An immediate challenge lies in understanding the nanometer-scale petrography of the ultrafine-grained aggregates in 'pyroxene' IDP's. Whether these aggregates contain components from diverse grain-forming environments may ultimately be answered by systematic petrographic studies using electron microscopes capable of high spatial resolution microanalysis. It may be more difficult to decipher evidence of grain formation and evolution in 'olivine' and 'layer silicate' IDP's because they appear to have experienced post-accretional alteration. Most of the studied 'olivine' IDPs have been subjected to heating and equilibration, perhaps during atmospheric entry, while the 'layer silicate' IDP's have experienced aqueous alteration.

Bradley, John↗
NASA NTRS1994

The origin and role of dust in the early solar system

Dust was the primary building material of the solar nebula planetesimals that accumulated to form minor planets, solid planets, and the cores of giant planets. Collected interplanetary dust particle (IDP) samples probably contain preserved samples of nebular dust that formed over a wide range of radial distance. There are two general source regions of IDP's, the asteroid belt and the short-period comets. The collected asteroid particles are likely to be rather representative samples of material that accreted into planetesimals in the 2.2 to 3.3 AU region. The comet samples are likely to be representative samples of grains that accreted in the Kuiper belt region between 20 AU and some hundreds of AU. Many of the solar system effects on grains should have been more pronounced or even restricted to the less than 5 AU region where the asteroids were formed. A major goal of IDP research is to try to identify typical asteroidal and cometary IDP's and to study their properties. If successful this will provide fundamental insight into both the initial solids in the solar nebula and materials modified by a variety of important nebular processes.

Brownlee, Don E.↗
NASA NTRS1997

Mid-Infrared Observational and Theoretical Studies of Star Formation and Early Solar Systems

The first 2 years of this program were used to make mid-IR observations of regions of star formation in the Orion nebula with the UCSD mid-IR camera at the UCSD/University of Minnesota telescope at Mt. Lemmon. These observations attempted to make the first systematic study of an extended region, known to have newly forming stars, and expected to have complex mid-IR emission. We discovered, to our surprise, that most of the thermal emission originated from extended sources rather than from point sources. This interesting observation made the analysis of the data much more complex, since the chop/nod procedures used at these wavelengths produce a differential measurement of the emission in one region compared to that in the adjacent region. Disentangling complex extended emission in such a situation is very difficult. In parallel with this work we were also observing comets in the thermal infrared, the other component of the original proposal. Some spectacular data on the comet Swift-Tuttle was acquired and published. A changing jet structure observed over a 2 week period is described. The rotation period of the comet can be measured at 66 hours. The size of the nucleus can also be estimated (at 30 km) from the observed excess flux from the nucleus. These data have lead to the development of models describing the action of dust particles of differing sizes and composition leaving the nucleus. The spatial distribution of the predicted IR emission has been compared to the observed jet structures, leading to estimates of both particles sizes, relative amounts of silicate vs organic grains, and the amounts of dust emitted in the jets vs isotopic emission.

Jones, Barbara↗
NASA NTRS2003

Microbeam Investigations of Presolar and Early Solar System Materials

This grant provided three years of funding to initiate an independent research program in Cosmochemistry at Arizona State University. Because the new equipment that was installed at ASU took longer than expected to get running, the project was extended for a fourth year with no additional funding. By the time the funds were expended, we had set up an entirely new ion microprobe laboratory at ASU, and we have been fully operational for over two years. This laboratory was funded in almost equal parts by NASA, NSF, and ASU. Papers describing the first results from this new laboratory are being published now, and the results have been making an impact on the Cosmochemistry community. While this laboratory was being built, I continued my research program in collaboration with G. J. Wasserburg at Caltech. As equipment became available, I gradually shifted my research to ASU. Over the lifetime of this grant, my research program resulted in 12 papers and 13 abstracts on topics ranging from presolar grains (2 papers, 3 abstracts), short-lived radionuclides (6 papers, 6 abstracts), chemical compositions of chondritic materials (3 papers, 3 abstracts), silicon isotopic fractionation (1 abstract), and the oxygen composition of the Sun (1 paper). The most important results of this period were the discovery of presolar hibonite in a meteorite residue, the measurement of 26A1 in CAIs from enstatite chondrites, and the measurements of 10Be in type A CAIs from CV chondrites. All of these results have had a significant impact on research in Cosmochemstry.

Huss, Gary R.↗
NASA NTRS2004

Chemical Constraints on the Early Solar System

Chemical abundances of comets and star-forming regions provide p o w d clues to the conditions which prevailed in the outer solar nebula. Hence comparative spectroscopic studies of cometary and molecular cloud gases provide vital insights into conditions in the solar protoplanetary disk at heliocentric distances beyond 5 AU 4.6 Gyr ago. We proposed a research program which combined optical and sub-millimeter techniques with laboratory spectroscopy, and sought to determine key diagnostic constraints on single-star protoplanetary disk models.

Wyckoff, Susan↗