Solar‐wind krypton and solid/gas fractionation in the Early Solar Nebula

Abstract

Krypton is the best candidate for determining limits on solid/gas fractionation in the early sun because of the smoothness of the odd‐mass abundance curve in its mass region, which permits relatively precise interpolations of its abundance assuming no fractionation. Here we calculate the solar‐system Kr abundance from solar‐wind noble‐gas ratios, determined previously by low‐temperature oxidations of lunar ilmenite grains, normalized to Si by spacecraft solar‐wind measurements. The estimated 83Kr abundance of 4.1 ± 1.5 per 106 Si atoms is within uncertainty of estimates assuming no fractionation, determined from CI‐chondrite abundances of surrounding elements. This is significant because it is the first such constraint on solid/gas fractionation, though the large uncertainty only confines it to somewhat less than a factor of two.