Near-equilibrium isotope fractionation during planetesimal evaporation

Understand

Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals.

• We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations.
• Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order < 1 meter that would be subject to foundering.
• Bodies that are massive enough to form magma oceans by radioisotope decay (ge 0.1%) can retain hot rock vapor even in the absence of ambient nebular gas.