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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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202 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Local and exotic components of primitive meteorites, and their origin

The chemical and isotopic compositions of chondrites and their implications for chondrite origins are considered, reviewing the results of recent theoretical and experimental investigations. Numerical data are compiled in tables and graphs and discussed in detail. Consideration is given to the properties and classifications of chondrites; components of local origin in the matrix, chondrules, Ca-Al-rich inclusions, and carbon and organic matter; exotic components such as O-16-enriched dust, nucleosynthetic anomalies, and extinct radionuclides; and isotopic anomalies of volatiles such as C, N, and the noble gases. The implications of the chondrite data for the stony fraction of comet nuclei are briefly indicated.

Anders, E.↗
DOE OSTI2025

Spectroscopy of the Hamburg Meteorite, Michigan H4

Spectroscopic studies of the Hamburg (Michigan H4) meteorite using visible–near-infrared (VNIR), mid-infrared (MIR), Raman, and Mössbauer data reproduce the results of more conventional laboratory measurements of petrology and geochemistry. This combination provides general information on the mineral modes of silicates, although spectroscopy was performed on different splits of this meteorite, and varying results may be explained by heterogeneity that is typical of ordinary chondrites. Raman also detects small features assigned to first-order D and G carbon bands, while Mössbauer data show the presence of Fe oxides and carbides. The electron microprobe (EMPA) composition of olivine in this meteorite is accurately measured to be Fo 81.3 , while MIR and Raman closely agree with Fo 80 and Fo 82 , respectively, and Mössbauer, at Fo 60 − Fo 70 , is in the ballpark. Similarly, P. R. Heck et al. report pyroxenes with compositions of Fs 16 Wo 1 , while Raman suggests a somewhat similar composition of Fs 28 Wo 0 . Both VNIR and MIR detect the presence of small amounts of feldspar, while EMPA identifies its composition as An 14 Ab 8 Or 5 . VNIR data were matched to spectral libraries of meteorite and asteroid data and shown to closely match other L and H meteorites. The best spectral matches to the Michigan H4 meteorite are to asteroid classes L/H/LL/URE, EH/EL/AUB, and CO/CV from M. D. Dyar et al.; objects in this group are intermediate in semimajor axis lengths for their orbits. The results highlight the strengths and weaknesses of each technique and show their collective strength when applied together to a single meteorite sample.

58 GEOSCIENCES↗
NASA NTRS1994

Effect of meteoroid rotation on atmospheric entry heating and meteor beginning height

The beginning height of a meteor varies by approximately 10 km depending on the rotation state of a spherical meteoroid as long as the body sustains a temperature gradient. Such gradients build up in friable stony meteoroids larger than approximately 0.1 cm and in iron meteoroids that are approximately 1 cm or larger. The height where 100 microns or smaller zodiacal dust particles ablate is nearly independent of rotation. Stony particles in the 100 microns size range ablate near 120 km while both larger and smaller meteoroids penetrate deeper. All calculations were made with a nominal speed of 30 km/s and a zenithal distance equal to z(sub r) = 0 deg. Larger meteoroids cool their surface by conduction to the interior while smaller meteoroids decelerate significantly due to their large surface area to mass ratio so that the surface receives a lower energy flux. Some micro-meteoroids smaller than approximately 10 microns may escape abalation altogether at the nominal velocity. The effect of rotation on particle temperature during atmospheric flight is significant on meteoroids larger than 0.1 cm but may be negligible on micro-meteorites that are typically 10-50 microns in diameter.

Adolfsson, L. G.↗
NASA NTRS1991

Characterization of low albedo asteroids

Three asteroid classes were defined from the early spectral surveys of the asteroids: C for carbonaceous, M for metallic, and S for stony. Subsequent spectral studies have defined new asteroid classes and have shown that the original classes can be divided into a number of additional asteroid types. The low albedo asteroids are now classified as types B, C, D, F, G, K and P. These types are concentrated in the middle asteroid belt and beyond. Their visible and near infrared spectra are generally featureless and dark, with a red slope in the ultraviolet. Some of them show water absorption features in the mid-infrared, indicating the presence of bound water. The lack of absorption features in the telescopic reflectance spectra has made it difficult to determine the mineralogy of the low albedo asteroids. Some of the asteroid spectra closely resemble laboratory spectra of carbonaceous chondrite meteorites, implying similar mineralogy. These meteorites are chemically primitive, composed of fine-grained matrix material which includes hydrous silicates, complex carbon compounds, olivine and pyroxene, combined with olivine and/or pyroxene chondrules. The main belt low albedo asteroids are probably very similar to these asteroids, but no meteoritic analogues exist for the most distant asteroid types.

Lebofsky, Larry A.↗