THE RECORD IN THE METEORITES. III. ON THE DEVELOPMENT OF METEORITES IN ASTEROIDAL BODIES

Journal Article · Fri Jul 01 00:00:00 EDT 1960 · Astrophysical Journal (U.S.)

DOI:https://doi.org/10.1086/146918· OSTI ID:4148402

Fish, R A; Goles, G G; Anders, E

It was proposed that the meteorites originated in planetesinals of asteroidal dimensions, heated by some transient internal energy source, such as extinct radioactivity. The usual objections to an origin in small bodies were examined and were shown to be unfounded. It was shown that segregation of metal and silicate phases and mineral differentiation by crystal settling will take place on reasonable time scales even in small bodies. Evidence concerning the occurrence of diamonds in meteorites was critically examined and wse found to be inconsistent with an origin in large bodies. Instead, it was decided that diamonds were formed as a metastable phase by decomposition of cohenite (Fe/sub 3/ C) under localized stresses or else upon impact with the earth (as proposed by Nininger). A detailed study of the thermal evolution of interually heated planetesimals was undertaken with a view to discovering spontaneous processes that might have led to the development of the meteorites. After the onset of melting, the equilibrium configuration of the planetesimals will comprise an inner core of metal and an outer core of silicate; a mantle of chondritic composition, compacted by sintering; and an unconsolidated surface layer. The expected properties of material from each of these strata agree well with those of the known classes of meteorites. Further temperature rise in the planetesimal will result in quasi-volcanic eruptions due to evolution of gases and vapors (e.g., elemental sulfur, carbon monoxide, silicon monosulfide) from the interior. This quasi-volcanic activity will cause extensive recycling of material and can lead to the development of many detailed features of the meteorites. Evidence was presented to show that the capillary veins in stone meteorites were produced by momentary action of hot, sulfur-containing gases. This was in accord with the proposed model. Another consequence of the model is the operation of a cyclic process that will deplete the chondritic mantle in some chalcophile elements, such as In, Tl, Pb, and Bi. This may account for the discrepancies between the observed and predicted abundances of these elements in chondrites. Possible energy sources were critically examined. Only extinct radioactivity seems to meet all requirements. In order for this source to have been important, it is necessary for the parent bodies of the meteorites to have accreted within 6 to 7 million years after nucleogenesis, in which case 7.3 x 10/sup 5/ year Al/sup 26/ could have provided an adequate source of heat, or that an uncharacterized nuclide with a half life of 10/sup 6/ to 10/sup 8/ years exists and was present in the early solar system. (auth)

• Research Organization: Univ. of Chicago
• NSA Number: NSA-14-023452
• OSTI ID: 4148402
• Journal Information: Astrophysical Journal (U.S.), Vol. Vol: 132; Other Information: Orig. Receipt Date: 31-DEC-60
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

PHYSICS
ALUMINUM 26
ASTROPHYSICS
BISMUTH
CARBON OXIDES
CRACKS
CRYSTALS
DIAMONDS
ENERGY
GASES
HALF-LIFE
HEATING
INDIUM
IRON CARBIDES
LEAD
MASS
MELTING
METALS
METEORITES
PLANETS
PRODUCTION
QUANTITY RATIO
RADIOACTIVITY
SILICATES
SILICON SULFIDES
SINTERING
SULFUR
SUN
TEMPERATURE
THALLIUM
THERMAL STRESSES
VAPORS