Pluto's structure and composition suggest origin in the solar, not a planetary, nebula

The four explanations for Pluto's large rock/ice ratio, (1) formation in the inner solar system, (2) volatile loss during accretion, (3) volatile loss during the large-body impact that created Charon, and (4) formation as a large, ice-poor outer solar system planetesimal, are considered. It is shown that only the last two explanations are feasible, and that the depletion of water ice in Pluto is so severe that both explanations may be necessary.