On possible explanation for the difference is that LENR processes are common. Harry NASA Mission Suggests Sun and Planets Constructed Differently http://www.spacedaily.com/reports/NASA_Mission_Suggests_Sun_and_Planets_Constructed_Differently_999.html "These findings show that all solar system objects including the terrestrial planets, meteorites and comets are anomalous compared to the initial composition of the nebula from which the solar system formed," said Bernard Marty, a Genesis co-investigator from Centre de Recherches Petrographiques et Geochimiques and the lead author of the other new Science paper. "Understanding the cause of such a heterogeneity will impact our view on the formation of the solar system."
