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Xenon fractionation in porous planetesimalsThe distinctively fractionated Xe on Mars and earth may have its root in a common source from which both planets accreted. Beginning with Ozima and Nakazawa's (1980) hypothesis that terrestrial Xe fractionation was caused by gravitational separation of adsorbed solar nebular gases inside large porous planetesimals, it is pointed out that Xe would have been trapped as the planetesimal grew and pores were squeezed shut by lithostatic pressure. It is shown that enough fractionated Xe to supply the earth could have been trapped this way. The degree of fractionation is controlled by the lithostatic pressure at the pore-closing front and so would have been roughly the same for all large planetesimals. The predicted degree of fractionation agrees well with that preserved in terrestrial and Martian Xe. Relative to Xe, this source is strongly depleted in other noble gases. In contrast to the original Ozima and Nakazawa hypothesis, the present hypothesis predicts the observed fractionation, and it allows planetary accretion to occur after the dissipation of the solar nebula.
Document ID
Document Type
Reprint (Version printed in journal)
Zahnle, Kevin (NASA Ames Research Center Moffett Field, CA, United States)
Pollack, James B. (NASA Ames Research Center Moffett Field, CA, United States)
Kasting, James F. (Pennsylvania State University University Park, United States)
Date Acquired
August 14, 2013
Publication Date
September 1, 1990
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 54
ISSN: 0016-7037
Subject Category
Distribution Limits