Chapter 22 Primordial Atmosphere Surrounding a Protoplanet and Formation of Jovian Planets : Part VI Growth of the Planets : Origin of the Solar System

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If a protoplanet accumulates in the solar nebula, a primordial atmosphere is formed surrounding the protoplanet. The atmosphere plays various roles in planetary formation. First, a high temperature develops at the bottom of the atmosphere because of the blanketing effect, and the surface materials of a protoplanet are molten if the planetary mass becomes greater than about one-third of Earth's mass. The geophysical implication of this high temperature is that an iron core is formed simultaneously with the accumulation of the protoplanet if the protoplanet grows beyond about 0.3 Earth's mass. Second, a small portion of the atmospheric gases dissolves inside the molten surface region of a protoplanet and another portion remains outside as a residue of the dissipated atmosphere. These retained components may account for Ne and Xe isotopic ratios of the present atmosphere of the Earth. Third, the instability of the primordial atmosphere forms the proto-giant-planet. This instability hypothesis can satisfy both the absolute value and the similarity of the core mass of the giant planets. However, a recent estimate of the long accumulation time for Uranus and Neptune suggests that these two planets were formed through the coalescence of small protoplanets with diffuse primordial atmospheres.
理論物理学刊行会の論文
1989-03-10