scholarly journals Cometary vs Asteroidal Origin of Chondritic Meteorites (Abstract)

1971 ◽  
Vol 13 ◽  
pp. 343-343 ◽  
Author(s):  
George W. Wetherill
Keyword(s):  
High Probability ◽  
Cosmic Ray ◽  
Low Velocity ◽  
Monte Carlo Calculations ◽  
Short Period ◽  
Mean Lifetime ◽  
The Mean ◽  
Alternative Sources ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

Monte Carlo calculations indicate excellent agreement between observed and predicted orbits of Prairie network fireballs, if it is assumed that fireballs are derived from remnants of short period comets of Jupiter’s family. No such satisfactory agreement has been found for any other proposed source. The distribution of radiants and time of fall observed for chondrites will also be reproduced by this source, provided that consideration is given to the fact that the Earth’s atmosphere will permit low velocity bodies to survive but will destroy high velocity bodies. Again, no other proposed source has been found to be adequate.It now appears likely that the mean lifetime of chondrites is limited to ˜107 yr by the high probability of complete fragmentation following impact by smaller bodies. This improves the agreement between the observed cosmic ray exposure ages and those predicted for a cometary source. This also requires some modification of the earlier discussions of alternative sources, but does not result in them becoming more satisfactory.

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 Several of the following arguments are based on new and unpublished results of rare gas measurements by HINTENBERGER, SCHULTZ und WÄNKE70.Bronzite-chondrites :1.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 tektites by the fission-track technique

1965 ◽  
Vol 70 (6) ◽  
pp. 1491-1496 ◽  
Author(s):  
R. L. Fleischer ◽  
C. W. Naeser ◽  
P. B. Price ◽  
R. M. Walker ◽  
M. Maurette
Keyword(s):  
Fission Track ◽  
Cosmic Ray ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

40Ar-39Ar and cosmic-ray exposure ages of nakhlites-Nakhla, Lafayette, Governador Valadares-and Chassigny

2011 ◽  
Vol 46 (9) ◽  
pp. 1397-1417 ◽  
Author(s):  
Ekaterina V. KOROCHANTSEVA ◽  
Susanne P. SCHWENZER ◽  
Alexei I. BUIKIN ◽  
Jens HOPP ◽  
Ulrich OTT ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

Meteorites with short cosmic-ray exposure ages, as determined from their Al26 content

1967 ◽  
Vol 31 (10) ◽  
pp. 1793-1809 ◽  
Author(s):  
Dieter Heymann ◽  
Edward Anders ◽  
M.W Rowe
Keyword(s):  
Cosmic Ray ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

scholarly journals Cosmic Ray Exposure Age Determinations of Cosmic Spherules from Marine Sediments

1985 ◽  
Vol 85 ◽  
pp. 179-181
Author(s):  
Kazuo Yamakoshi
Keyword(s):  
Mass Spectrometry ◽  
Cosmic Ray ◽  
High Energy ◽  
High Energy Accelerator ◽  
Exposure Age ◽  
Cosmic Spherules ◽  
Inner Region ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Age ◽  
Cosmic Ray Exposure Ages

AbstractThe cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.

scholarly journals Noble Gas Record of Japanese Chondrites

1989 ◽  
Vol 44 (10) ◽  
pp. 935-944
Author(s):  
Nobuo Takaoka ◽  
Masako Shima ◽  
Fumitaka Wakabayashi
Keyword(s):  
Noble Gas ◽  
Cosmic Ray ◽  
Ordinary Chondrites ◽  
Isotopic Signatures ◽  
Shock Heating ◽  
H Chondrites ◽  
Gas Loss ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages ◽  
Gas Component

Abstract Concentrations and isotopic ratios of noble gases are reported for nineteen Japanese chondrites. Among those, Nio (H3-4) is a solar-gas-rich meteorite.U/Th - He ages are younger than K - Ar ages for all meteorites studied. Six of the nine L-chondrites give significantly young K-Ar ages, suggesting gas loss by impact shock heating. The remaining three L-chondrites and seven of the ten H-chondrites have K-Ar ages older than 4 Ga. The L-chondrite Nogata and the H-chondrites Numakai, Ogi and Higashi-Koen have concordant ages.Cosmic-ray exposure ages for six of the H-chondrites show clustering around the 6-Myr peak in the distribution of exposure ages, while those for the L-chondrites, ranging from 8.2 to 64 Myr, do not show clustering.Fukutomi (L4) contains trapped 36Ar in excess, 3.5 times enriched compared to the highest value so far reported for type-4 ordinary chondrites except solar-gas-rich chondrites. The 36Ar/132Xe and 84Kr/132Xe ratios fit along a mixing line between a planetary and a sub-solar (or argon-rich) component found in separates of E-chondrites [43], The Xe isotopic composition is identical with that in Abee and Kenna. The isotopic signatures suggest that this meteorite may contain mineral fragments bearing the noble gas component found in E-chondrites or ureilites. Fukutomi also contains 80Kr, 82Kr and 128Xe produced by epithermal neutron captures on 79Kr, 81Kr and 127I, respectively. From the neutron-produced Kr, the preatmospheric minimum radius is estimated to be 20 cm with an assumption of a spherical meteoroid.

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.

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