COSMOCHEMICAL CONSTRAINTS ON THE ORIGIN AND EARLY GEOLOGICAL EVOLUTION OF POTENTIAL EXTRASOLAR EARTH-LIKE PLANETS

摘要

Conventional solar nebula models on planetary formation suggest that the composition of planets formed around a star strongly depends on the chemistry of the initial molecular cloud. Equilibrium condensation calculations carried out in this work suggest that some astrochemical environments similar in composition to a solar-like nebula may yield (1) systems with dust/gas ratios very high relative to solar nebula values, and (2) protoplanetary materials where graphite becomes a stable phase at C/O ratios as low as 0.6. According to canonical models of condensation, gravitational colapse, disk formation and accretion, rocky planets may form in these environments in ways analogous to those of our solar system. The early geological evolution of such planets will be controlled esentially by their mass and mineralogical composition of condensates. This work provides constraints on accretion efficiency (based on initial dust/gas values), bulk chemical composition and primary differentiation processes (core segregation, crust formation) of potential Earth-like planets formed around solar-like stars.