Noble gas isotopic fractionation between solar wind and the Sun, And implications for Genesis solar wind oxygen measurements

Abstract

We urge that He is the best case for a meaningful estimation of solar composition without measurement of solar wind (SW) composition; the value of such an estimation is that it may then be compared to the actual measurements, thereby leading to an empirical constraint on the degree of isotopic fractionation arising in SW and thence to how much fractionation may have affected the SW composition of other elements. We take primordial 3He/4He to be as identified in the so-called Q component identified in meteoritic materials. In the Sun, however, 3He/4He is higher because of the augmentation of 3He by D-burning, the nuclear conversion of primordial deuterium. After accounting for the D-converted 3He, we estimate 3He/4He in the present Sun (post-D burning He), and then, from the difference between this and the 3He/4He found in Genesis SW, we estimate the isotopic fractionation between them. Then, from noble gas systematics, we show that Genesis SW noble gases may be related to Q-noble gases by a mass-dependent Rayleigh-type fractionation. We develop a kinetic description of isotopic fractionation of minor components in SW relative to the solar atmosphere, which is consistent with the Rayleigh-type fractionation. This predicts fractionation in the O mass range, which is significantly different from the value used by Heber et al. (2011). The latter value corresponds to the premise that Ca-Al-rich inclusion O is the same as solar O, whence this work does not support that premise. © 2012 The Meteoritical Society.