Engineering topics

Nuth, J. A.

Publications and source records attributed to Nuth, J. A..

At least 19 records

NASA NTRS2017

Formation Mechanism of Iron-Rich Olivine: Experimental Constrains into Early Fluid-Assisted Hydration and Dehydration Processes on Asteroids

Iron-rich olivine is one of the major minerals in the matrices of unequilibrated ordinary (UOCs) and carbonaceous (CV, CK, CO) chondrites whose petrologic type is >3.1. There has been an extensive discussion in the literature as to the formation mechanism of these olivines; however, their origin is poorly understood. The formation of ferroan olivine during hydrothermal alteration has been demonstrated to be thermodynamically viable. The stability of ferroan olivine is highly dependent on several variables, including temperature, water/ rock (W/R) ratio, pressure, oxygen fugacity, and bulk rock composition. So far, hydrothermal alteration experiments have not been successful at forming FeO-rich olivines with the compositions and textures observed in the matrices of chondrites. Therefore, understanding the formation conditions of FeO-rich olivines remains a key problem to explain the effects of hydrothermal alteration on chondrite matrices.

Iron-rich olivine↗

NASA NTRS2017

Refractory Organics in Comet 67P Churyumov-Gerasimenko: Additional Evidence for Large-scale Mixing in the Primitive Solar Nebula?

The COSIMA instrument onboard the Rosetta spacecraft collected and analyzed samples of individual particles from the coma of Comet67P/ Churyumov-Gerasimenko. Initial results of the analysis of several particles have been presented elsewhere while analyses of the organic component of the dust particles has been shown to compare favor ably to laboratory spectra of IOM extracted from the Orguil and Murchison meteorites. Here we will compare the spectra of the same two particles to laboratory spectra of organic grain coatings produced via Surface Mediated Reactions of CO, H2 and N2 on amorphous iron silicate grains.

Refractory Organics↗

NASA NTRS2015

The OSIRIS-REx Contamination Control and Witness Strategy

The OSIRIS-REx mission (Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer) is the third NASA New Frontiers mission. It is scheduled for launch in 2016. The primary objective of the mission is to return at least 60 g of "pristine" material from the B-type near- Earth asteroid (101955) Bennu, which is spectrally similar to organic-rich CI or CM meteorites [1]. The study of these samples will advance our understanding of materials available for the origin of life on Earth or elsewhere. The spacecraft will rendezvous with Bennu in 2018 and spend at least a year characterizing the asteroid before executing a maneuver to recover a sample of regolith in the touch-and-go sample acquisition mechanism (TAGSAM). The TAGSAM and sample is stowed in the sample return capsule (SRC) and returned to Earth in 2023.

New Frontiers mission↗

NASA NTRS2013

Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Wavelength and Temperature

The Optical Properties of Astronomical Silicates with Infrared Techniques program utilizes multiple instruments to provide spectral data over a wide range of temperatures and wavelengths. Experimental methods include Vector Network Analyzer and Fourier transform spectroscopy transmission, and reflection/scattering measurements. From this data, we can determine the optical parameters for the index of refraction, n, and the absorption coefficient, k. The analysis of the laboratory transmittance data for each sample type is based upon different mathematical models, which are applied to each data set according to their degree of coherence. Presented here are results from iron silicate dust grain analogs, in several sample preparations and at temperatures ranging from 5 to 300 K, across the infrared and millimeter portion of the spectrum (from 2.5 to 10,000/micron or 4000 to 1/cm).

Dust↗

NASA NTRS2013

Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Wavelength and Temperature

The Optical Properties of Astronomical Silicates with Infrared Techniques (OPASI-T) program utilizes multiple instruments to provide spectral data over a wide range of temperature and wavelengths. Experimental methods include Vector Network Analyzer (VNA) and Fourier Transform Spectroscopy (FTS) transmission, and reflection/scattering measurements. From this data, we can determine the optical parameters for the index of refraction, n, and the absorption coefficient, k. The analysis of the laboratory transmittance data for each sample type is based upon different mathematical models, which are applied to each data set according to their degree of coherence. Presented here are results from iron silicate dust grain analogs, in several sample preparations and at temperatures ranging from 5-300 K, across the infrared and millimeter portion of the spectrum (from 2.5-10,000 μm or 4,000-1 cm(exp −1).

Optical↗

NASA NTRS2013

Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Wavelength and Temperature

Methods: laboratory↗

NASA NTRS2012

The Osiris-Rex Mission - Sample Acquisitions Strategy and Evidence for the Nature of Regolith on Asteroid (101955) 1999 RQ36

NASA selected the OSIRIS-REx Asteroid Sample Return Mission as the third New Frontiers mission in May 2011 [I]. The mission name is an acronym that captures the scientific objectives: Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer. OSIRIS-REx will characterize near-Earth asteroid (101955) 1999 RQ36, which is both the most accessible carbonaceous asteroid [2,3] and one of the most potentially hazardous asteroids known [4]. The primary objective of the mission is to return a pristine sample from this bod, to advance our understanding of the generation, evolution, and maturation of regolith on small bodies.

Lauretta, D. S.↗

NASA NTRS2011

A Quantitative, Time-Dependent Model of Oxygen Isotopes in the Solar Nebula: Step one

The remarkable discovery that oxygen isotopes in primitive meteorites were fractionated along a line of slope I rather than along the typical slope 0,52 terrestrial fractionation line occurred almost 40 years ago, However, a satisfactory, quantitative explanation for this observation has yet to be found, though many different explanations have been proposed, The first of these explanations proposed that the observed line represented the final product produced by mixing molecular cloud dust with a nucleosynthetic component, rich in O-16, possibly resulting from a nearby supernova explosion, Donald Clayton suggested that Galactic Chemical Evolution would gradually change the oxygen isotopic composition of the interstellar grain population by steadily producing O-16 in supernovae, then producing the heavier isotopes as secondary products in lower mass stars, Thiemens and collaborators proposed a chemical mechanism that relied on the availability of additional active rotational and vibrational states in otherwise-symmetric molecules, such as CO2, O3 or SiO2, containing two different oxygen isotopes and a second, photochemical process that suggested that differential photochemical dissociation processes could fractionate oxygen , This second line of research has been pursued by several groups, though none of the current models is quantitative,

Nuth, J. A.↗

NASA NTRS2011

Carbon Isotopic Fractionation During Formation of Macromolecular Organic Grain Coatings via FTT Reactions

Observations of carbon isotopic fractionation of various organic compounds found in meteorites may provide useful diagnostic information concerning the environments and mechanisms that were responsible for their formation. Unfortunately, carbon has only two stable isotopes, making interpretation of such observations quite problematic. Chemical reactions can increase or decrease the C-13/C-12 ratio by various amounts, but the final ratio will depend on the total reaction pathway followed from the source carbon to the final product, a path not readily discernable after 4.5 billion years. In 1970 Libby showed that the C-13/C-12 ratios of terrestrial and meteoritic carbon were similar by comparing carbon from the Murchison meteorite to that of terrestrial sediments. More recent studies have shown that the C-13/C-12 ratio of the Earth and meteorites may be considerably enriched in C-13 compared to the ratio observed in the solar wind [2], possibly suggesting that carbon produced via ion-molecule reactions in cold dark clouds could be an important source of terrestrial and meteoritic carbon. However, meteoritic carbon has been subjected to parent body processing that could have resulted in significant changes to the C-13/C-12 ratio originally present while significant variation has been observed in the C-13/C-12 ratio of the same molecule extracted from different terrestrial sources. Again we must conclude that understanding the ratio found in meteorites may be difficult.

Nuth, J. A.↗

NASA NTRS2005

The Vapor Pressure of Palladium at Temperatures up to 1973K

Understanding high-temperature processes is imperative for modeling the formation of the solar system. It is unfortunate that since the 1950 s little has been done in the area of thermodynamics to continue gaining information on metals such as iron (Fe), nickel (Ni), cobalt (Co), palladium (Pd) and many others. Although the vapor pressures of these metals can be extrapolated to higher temperatures, the data is often limited to temperature ranges too low to be applicable to processes that occur during the formation of the solar system (T approx. 2000K). Experimental techniques inhibited the data in the past by restricting the testing of metals to temperatures below their melting point. Today, higher temperature testing is possible by using a Thermo- Cahn Thermogravimetric system that is able to reach temperatures up to 1973K in vacuo and measure a 10 gram change in a sample with mass of up to 100 grams.

Gardner, K. G.↗

NASA NTRS2005

Phototelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and the equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much higher than the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of approximately 0.09 to 8 microns radii levitated in an electrodynamic balance and illuminated with W radiation at 120 to 160 nm wavelengths. The measured values and the size dependence of the yields are found to be substantially different from the bulk values given in the literature.

Abbas, Mian M.↗

NASA NTRS2004

Effusion Cell Measurements of the Vapor Pressure of Cobalt at Temperatures up to 2000K; Comparisons with Iron and Nickel

It has become increasingly clear over the past decade that high temperature processes played important roles in the Primitive Solar Nebula. Unfortunately, basic data, such as the vapor pressures of Fe, Ni, Co or SiO have not been measured over the appropriate temperature range (near T approx. 2000K), but must be extrapolated from lower temperature measurements often made more than 50 years ago. The extrapolation of the available data to higher temperatures can be quite complex (e.g., see [1] for SiO vapor pressures) and can depend on other factors such as the oxygen fugacity or the presence of hydrogen gas not accounted for in the original measurements. Moreover, modern technology has made possible more accurate measurements of such quantities over a wider temperature range. We have acquired a commercial Thermo-Cahn Thermogravimetric system capable of vacuum operation to 1700C and measurement of a 10g change in sample mass using up to a 100g sample, with microgram accuracy. With this new system we have initiated a series of basic vapor pressure measurements on simple metals such as Fe[2] and Ni[3] with the intention to extend such measurements to more complex systems once we gain sufficient experience.

Nuth, J. A.↗

NASA NTRS2004

Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System

Comets, fine-grained matrices of chondrites, and chondritic interplanetary dust particles (IDPs) are each composed of both crystalline and amorphous silicates. The primitive solar nebula, in which comets and asteroids accreted, was formed from the collapsed core of a Giant Molecular Cloud, that, in turn, condensed from materials present in the interstellar medium (ISM). Despite observations that reveal the presence of crystalline magnesium silicate minerals in the shells of very high mass-loss-rate stars [1,2], typical silicate grains in the ISM are most likely to be amorphous, given their relatively long residence time in such a high radiation environment. An upper limit of ~3% crystalline grains can be derived from their non-detection in spectra of ISM solids [3]. If the vast majority of grains that enter the primitive solar nebula are amorphous, then the observation of crystalline dust in comets and primitive chondrite matrices indicates the action of specific processes required to transform the amorphous starting materials into the crystals that are observed.

Nuth, J. A.↗

NASA NTRS2003

Chemical Analysis of Primitive Objects Using a Slitless Ultraviolet Meteor Spectrometer (CAPO-SUMS)

Measure the elemental composition in both random meteors and in the bolides forming specific meteor streams (these are traceable to specific small bodies in the solar system). These will yield the average chemical composition and degree of chemical variability in a statistically significant number of planetesimals. CAPO-SUMS is functionally equivalent to a series of multiple, small-body sample analysis missions, but provides much more analytical capability than is possible on any orbital or flyby mission due to the vaporization, ionization and ultraviolet emission from the ablating bolide as it enters the atmosphere. CAPO-SUMS will provide a chemical context from which the detailed analytical studies provided by a cometary or asteroidal lander mission can be interpreted.

Nuth, J. A.↗

NASA NTRS2003

An Observational Test for Shock-induced Crystallization of Cometary Silicates

Crystalline silicates have been observed in comets and in protostellar nebulae, and there are currently at least two explanations for their formation: thermal annealing in the inner nebula, followed by transport to the regions of cometary formation and in-situ shock processing of amorphous grains at 5 - 10 AU in the Solar Nebula. The tests suggested to date to validate these models have not yet been carried out: some of these tests require a longterm commitment to observe both the dust and gas compositions in a large number of comets. Here we suggest a simpler test.

Nuth, J. A.↗

NASA NTRS2000

Noble Gas Incorporation into Graphitic "Smokes"

Graphitic smokes were condensed in noble gas atmospheres and analyzed for xenon. Results show trapping of amounts greater than found in chondritic carbonaceous residues. Sites saturated at low pressures. No mass-dependent fractionation was observed.

Olson, E. K.↗

NASA NTRS1999

Nucleation, Growth, Annealing, and Coagulation of Refractory Oxides and Metals: Recent Experimental Progress and Applications to Astrophysical Systems

Starting with cooling, refractory vapors diluted in significant quantities of H and He there are four processes that most natural systems will undergo: nucleation, growth, annealing, and coagulation. Nucleation is the processes by which the first stable refractory nuclei form in the vapor. These are the seeds onto which the remaining vapors will condense during the growth stage. Solids of any composition will try to arrange themselves into the least energetic configuration, provided that there is sufficient energy available to support such processes as diffusion and the breaking of chemical bonds. There is a significant activation energy associated with the annealing process in refractory solids due to the relatively high energy of the chemical bonds in solids. The grains formed in most cosmochemical systems are extremely small and often tightly coupled to the gas. Because of their small physical cross sections coagulation may be a very slow process unless there is another driving force involved in addition to normal Brownian motion. In what follows we will briefly cover each of these four stages for refractory oxide and metal grains, although in inverse order.

Nuth, J. A.↗

NASA NTRS1989

Proton irradiation of SiH4-Fe(CO)5-H2O ices - Production of refractory silicates and implications for the solar nebula

The results of a number of experiments are reported in which SiH4-Fe(CO)5-H2O ice mixtures were irradiated by 1 MeV protons at 15 K and then warmed to room temperature in approximately 50 K steps. The properties of a sample were monitored by observing its infrared absorption spectrum as a function of its processing history. In each experiment in which ice samples containing SiH4 were irradiated, a refractory amorphous silicate residue remained after warming to room temperature. In addition to the usual broad silicate features at 10 and 20 microns, features due to water or hydroxyl at 3 and 6.2 microns, and a feature due to CO at 5 microns, a surprisingly stable infrared feature at 4.6 microns, attributed to the SiH stretching fundamental, was observed.

Nuth, J. A.↗