Investigations of Cosmic-Ray-Produced Nuclides in Iron Meteorites: 5. More Data on the Nuclides of Potassium and Noble Gases, on Exposure Ages and Meteoroid Sizes

1983 ◽  
Vol 38 (2) ◽  
pp. 273-280 ◽  
Author(s):  
H. Voshage ◽  
H. Feldmann ◽  
O. Braun
Keyword(s):  
Noble Gases ◽  
Cosmic Ray ◽  
Parent Body ◽  
Critical Examination ◽  
Iron Meteorites ◽  
Abundance Patterns ◽  
New Information ◽  
Abundance Anomalies ◽  
Chemical Groups ◽  
Exposure Ages

Abstract The concentrations of the cosmic-ray-produced He-, Ne-, and Ar-nuclides in samples of 31 iron meteorites have been determined by mass spectrometry. Thereby, the number of samples analyzed in this laboratory has grown to 83. A critical examination of all these results was performed. The data of at least 52 samples prove to be useful to describe the "normal" abundance patterns of cosmogenic noble gases in iron meteorites; the description is accomplished by a new system of equations that correlate some properly selected abundance ratios with one another. The correlations serve as an instrument to recognize and diagnose certain abundance anomalies (3He-or 38Ar-deficiencies) which occur in about 25% of all samples analyzed. They allow to select those data which may unhesitatingly be applied in calculations concerning the irradiation histories of the respective meteorites. Another matter of concern for establishing these histories are the cosmic-ray-exposure ages. Mass spectrometric abundance analyses on meteoritic potassium have provided new data on the 41K/40K exposure ages of about 10 iron meteorites as well as on meteoroid sizes and sample depths. For two meteorites of the chemical group IIIAB, Joe Wright Mountains and Picacho, the age values obtained are 685 and 635 Ma, respectively. The results confirm our previous conclusion that the IIIAB-irons resided originally within a more or less contiguous partial volume (metallic core?) of their parent body and were ejected in consequence of a single impact event that happened about 670 Ma ago. Another motive for the present investigation was to measure the exposure ages for meteorites of the chemical groups IIICD and HIE. However, the new information obtained on their age distributions is still inadequate to answer some old questions concerning a possible relationship to the event that produced the IIIAB-meteoroids 670 Ma ago.

scholarly journals 3. Fragmentation of Asteroids and Delivery of Fragments to Earth

1977 ◽  
Vol 39 ◽  
pp. 283-291 ◽  
Author(s):  
G. W. Wetherill
Keyword(s):  
Cosmic Ray ◽  
Asteroid Belt ◽  
Combined Effects ◽  
Iron Meteorites ◽  
Exposure Age ◽  
Impact Rate ◽  
Dynamical Time ◽  
Spectrophotometric Data ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

Earth-impacting meteoroids are derived from both comets and asteroids, and some uncertainty still exists regarding with which of these bodies some stone meteorites should be identified. In contrast, the long cosmic ray exposure ages of iron meteorites strongly suggest a long-lived asteroidal source capable of providing ~108 g/yr of this material to the earth’s surface over at least much of solar system history. Spectrophotometric data show that differentiated asteroids are concentrated in the inner portion of the asteroid belt. The orbital histories of fragments of inner belt asteroids are investigated, considering the combined effects of close planetary encounters, secular perturbations, and secular resonances. Particular attention is given to the low inclination (<15°) objects with small semimajcr axis (2.1 to 2.6 A.U.), which can make fairly close approaches to Mars (<0.1 A.U.). It is found that the annual yield and dynamical lifetime of collision fragments of these asteroids is in agreement with the observed impact rate and exposure age of iron meteorites. A smaller yield of stone meteorites (-107 g/yr) is expected, because elimination of these objects by collision is probable on the long dynamical time scaTe. Achondrites could be produced in this way; the yield is probably too low to account for chondrites. Chondrites could possibly be derived indirectly from these bodies insofar as these asteroids are also sources of Apollo and Amor objects.

Das Strahlungsalter der Eisenmeteorite aus Chlor-36-Messungen

1961 ◽  
Vol 16 (4) ◽  
pp. 379-384 ◽  
Author(s):  
Else Vilcsek ◽  
H. Wanke
Keyword(s):  
Cosmic Ray ◽  
Decay Rates ◽  
Sikhote Alin ◽  
Iron Meteorites ◽  
Exposure Age ◽  
Exposure Ages ◽  
Chlorine 36

Chlorine 36, which is produced by the interaction of cosmic ray particles with nuclei in meteorites, was measured in seven iron meteorites and in one stone meteorite. The decay rates for chlorine-36 in iron meteorites varied between 6.5 and 20.2 dpm/kg. From these and from the concentration of stable spallation products, the exposure ages of these meteorites were calculated. In this way we found for six of the meteorites examined exposure ages close to 500 million years. Only for the Sikhote Alin meteorite the quite different exposure age of 60 million years was measured. As this value is also definitely lower than that found by other authors for this meteorite, it is suggested that the Sikhote Alin had been part of a bigger meteorite which was broken into pieces about 60 million years ago by a collision with another meteorite.

Der Mond als Mutterkörper der Bronzit-Chondrite

1966 ◽  
Vol 21 (1-2) ◽  
pp. 93-110 ◽  
Author(s):  
H. Wänke
Keyword(s):  
Age Distribution ◽  
Cosmic Ray ◽  
Parent Body ◽  
Gas Content ◽  
Rare Gas ◽  
Rare Gases ◽  
The Mean ◽  
Gas Measurements ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

Knowing the cosmic ray exposure ages of a sufficiently large number of meteorites and using the earth as analyser with special assumptions, criteria can be found to distinguish between a lunar or asteroidal origin of meteorites. Several of the following arguments are based on new and unpublished results of rare gas measurements by HINTENBERGER, SCHULTZ und WÄNKE70.Bronzite-chondrites :1. Arguments for an origin near the surface of the parent body. a) Porosity of the chondrites 0—20%. b) Many bronzite-chondrites contain light primordial rare gases, originating from the exposure of the single meteorite grains to the solar wind. c) Primordial rare gas content always connected with light-dark structure. d) In the distribution of the cosmic ray exposure ages certain groupings can be distinguished. The age distribution of bronzite-chondrites with light primordial rare gases is identical with the distribution of the cosmic ray exposure ages of all bronzite-chondri-tes. The bronzite-chondrites containing primordial gas therefore are probably coming from the very upper layers, and the other bronzite-chondrites from somewhat deeper layers of their parent body.2. Arguments for an origin close to the earth’s orbit. a) Bronzite-chondrites with high cosmic ray exposure ages show a slight tendency to fall in the afternoon (noon until midnight) . b) For the bronzite-chondrites, which are morning falls (midnight until noon), diffusion losses of 3He and 4He are higher and more frequent compared to the afternoon falls. The reason for this can be found in a closer approach to the sun of the first ones. Hypersthene-chondrites do not show this effect. c) Bronzite-chondrites with light primordial rare gas content concentrate among the afternoon falls. d) The mean cosmic ray exposure age of the bronzite-chondrites is considerably lower than that of the hypersthene-chondrites.3. Arguments concerning the size of the parent body. Light primordial rare gas and their connection with light-dark structure indicate a parent body of the size of the moon or a large asteroid.None of these arguments are strictly conclusive. In some cases they are based on observations, which can only be obtained by using statistical methods. Most of these effects are close to the mean error. Adding, however, all observations together, a lunar origin of the bronzite-chondrites becomes nearly undoubtable. A lunar origin of stone meteorites was in recent times first proposed by URET 3.Hypersthene-chondrites :Hypersthene-chondrites with low cosmic ray exposure ages are rare among the morning falls. Their parent body therefore probably has to be found outside the earth’s orbit. Their distribution of the cosmic ray exposure ages may also lead to this conclusion. As proposed by ANDERS 4, the Mars asteroids could possibly be the parent bodies for the hypersthene-chondrites. Mars itself might however be considered also. A lunar origin of the hypersthene-chondrites seems to be completely out of question.

Cosmic-ray exposure ages of diogenites and the recent collisional history of the howardite, eucrite and diogenite parent body/bodies

1997 ◽  
Vol 32 (6) ◽  
pp. 891-902 ◽  
Author(s):  
KEES C. WELTEN ◽  
LOUIS LINDNER ◽  
KLAAS BORG ◽  
THOMAS LOEKEN ◽  
PETER SCHERER ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Parent Body ◽  
History Of ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages
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