Al-26 as an asteroidal heat source?

Details Al-26 as an asteroidal heat source? Al-26 as an asteroidal heat source?

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.500m&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 500-501

Astronomy and Astrophysics

Astronomy

Aluminum Isotopes, Asteroids, Astronomical Models, Radioactive Isotopes, Thermodynamic Properties, Chondrule, Feldspars, Radioactive Age Determination, Radioactive Decay, Recrystallization, Spinel

Scientific paper

Thermal modeling suggests that the short-lived radionuclide Al-26 was a plausible asteroidal heat source. Heliocentric variations in the thermal properties of main belt asteroids inferred from their spectra can be explained by the incorporation of different amounts of Al-26, which varied as a function of the time required to accrete objects farther from the Sun. Quantification of this hypothesis requires a variation in accretion times across the asteroid belt on the order of several half-lives of Al-26, which is consistent with what is known about the lifetime of the nebula. Resistance to this idea derives from legitimate concerns about several assumptions implicit in the model: that Ca-Al rich inclusions (CAIs) adequately define an initial nebular Al-26/Al-27 value, that live Al-26 was widespread and homogeneously distributed, and that asteroids accreted promptly. The incorporation of Al-26 in a basaltic pebble and in an ordinary chondrite suggests that this nuclide was not restricted to refractory materials. The conclusion that Al-26 was widely distributed in the early solar system is strengthened by the discovery in the interstellar medium of a gamma-ray line from Al-26 decay. An apparent deficiency of Mg-26 in chondrule feldspars may suggest heterogeneous distribution, but could also reflect later crystallization of these grains from glass during parent-body metamorphism. A 3-4-m.y. lag time between the formation of CAIs and their incorporation into carbonaceous chondrite parent bodies, as judged from more Mg-26 in primary than secondary minerals is consistent with the 2-5-m.y. accretionary interval required by the Al-26 heating model for C asteroids at 2.7-3.4 AU. This discovery may support, not refute, an Al-26 heating model.

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