Differentiation of Planetesimals and the Thermal Consequences of Melt Migration

Дата и время публикации : 2011-01-21T15:47:28Z

Авторы публикации и институты :
Nicholas Moskovitz (Dept. of Terrestrial Magnetism, Carnegie Institution of Washington)
Eric Gaidos (Dept. of Geology and Geophysics, University of Hawaii)

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 33 pages, 5 figures, accepted to Meteoritics and Planetary Science
Первичная категория: astro-ph.EP

Все категории : astro-ph.EP

Краткий обзор статьи: We model the heating of a primordial planetesimal by decay of the short-lived radionuclides Al-26 and Fe-60 to determine (i) the timescale on which melting will occur; (ii) the minimum size of a body that will produce silicate melt and differentiate; (iii) the migration rate of molten material within the interior; and (iv) the thermal consequences of the transport of Al-26 in partial melt. Our models incorporate results from previous studies of planetary differentiation and are constrained by petrologic (i.e. grain size distributions), isotopic (e.g. Pb-Pb and Hf-W ages) and mineralogical properties of differentiated achondrites. We show that formation of a basaltic crust via melt percolation was limited by the formation time of the body, matrix grain size and viscosity of the melt. We show that low viscosity (< 1 Pa-s) silicate melt can buoyantly migrate on a timescale comparable to the mean life of Al-26. The equilibrium partitioning of Al into silicate partial melt and the migration of that melt acts to dampen internal temperatures. However, subsequent heating from the decay of Fe-60 generated melt fractions in excess of 50%, thus completing differentiation for bodies that accreted within 2 Myr of CAI formation (i.e. the onset of isotopic decay). Migration and concentration of Al-26 into a crust results in remelting of that crust for accretion times less than 2 Myr and for bodies >100 km in size. Differentiation would be most likely for planetesimals larger than 20 km in diameter that accreted within ~2.7 Myr of CAI formation.

Category: Physics