Supply and loss of volatile constituents during the accretion of terrestrial planets.
Abstract
The different densities of the terrestrial planets are evidence for differences in their chemical composition. According to the two-component model, the composition of terrestrial planets can successfully be described as mixtures of a highly reduced volatile-free component and an oxidized, volatiles-containing component. Mars obviously accreted homogeneously, while inhomogeneous accretion is favored for the Earth. Accretion is the most effective degassing stage of planetary matter; however, the early atmosphere formed in this way is also continuously removed by the accretion process itself. Large portions of Venus and the Earth, but not of Mars, became at least partially molten to great depth and, hence, had vigorously convecting mantles. Depending on their solubilities, the gases (HCl, H2O, CO2, rare gases, etc.) temporarily present in the early atmospheres entered these melts and were carried into the deep interiors. The present atmospheres of Venus, Earth and Mars are "secondary" atmospheres, while the "primary" atmospheres were almost completely lost. The huge differences observed in the concentrations of primordial rare gases per unit planetary mass on Venus, Earth and Mars are explained by differences in the amount of gases lost during accretion. The giant impact which probably formed the Moon also should have played an important role in the case of the Earth.
- Publication:
-
Origin and Evolution of Planetary and Satellite Atmospheres
- Pub Date:
- 1989
- Bibcode:
- 1989oeps.book..268D
- Keywords:
-
- Planetary Atmospheres;
- Planetary Composition;
- Planetary Evolution;
- Terrestrial Planets;
- Atmospheric Composition;
- Chemical Composition;
- Degassing;
- Gas Evolution;
- Astrophysics;
- Terrestrial Planets: Accretion;
- Terrestrial Planets: Chemical Composition;
- Terrestrial Planets: Planetary Atmospheres