© Lloyd, Charles Chandler

 

AIR & WATER ORIGIN

"The origin of water on Earth is still puzzling. At one end of the models, the high temperature in the inner accretion disk hampered hydrous phases to exist so that external sources were needed, the so-called late veneer of comets, asteroids and/or meteorites suggested by lunar cratering. At the other end, Earth accreted hydrous silicate phases, or grains having adsorbed water from the solar nebula."9

"Under reasonable assumptions, we find that no more than a few percent of Earth's water can be attributed to comets."9

"The larger the planet becomes, the less likely a given impact can melt the entire depth of the mantle (even the putative Moon-forming impact with the Earth may only have melted it to 2000 km depth)."4

"Almost all minerals that solidify from a bulk Earth magma composition are also denser than their coexisting magma. Solidification will therefore proceed from the bottom upward, with increasingly evolved magmas lying above growing layers of solid silicate minerals." "Because water and carbon are only minimally incorporated in these minerals, the magma is increasingly enriched in water and carbon compounds as solidification proceeds."4

Each impact continues the process of degassing and moving magma ocean liquids toward the planetary surface. "These impacts might be expected to blow off about half of the surface volatiles."4

"Late-stage magma ocean liquids will eventually become so enriched with water as to be... super-critical water oceans." It "is then effectively a hot water ocean."4

"A planetary atmosphere will not likely grow gradually, but will degas catastrophically toward the end of solidification".4

Most volatile elements in a planet are "degassed into the atmosphere during the end of magma ocean solidification, leaving only a small fraction of the original volatiles to be released into the atmosphere through later volcanism. Rocky planets that accrete with water in their bulk mantle have two mechanisms for producing an early water ocean: First, if they accrete with at least 1 to 3% by mass of water in their bulk composition, liquid water may be extruded onto the planetary surface at the end of magma ocean solidification. Second, at initial water contents as low as 0.01% by mass or lower, during solidification a massive supercritical fluid and steam atmosphere is produced that collapses into a water ocean upon cooling." For Earth, "the more probable source for early water oceans is the collapse of the planet's steam atmosphere."4

Considering planets with masses roughly similar to Earth, "if these planets began with 0.1% by mass water, the global ocean resulting from atmospheric collapse would be 1 to 10 kilometers deep, and beginning with 0.5% by mass water results in global water oceans tens of kilometers deep."4

"3% by mass is the maximum water content found in meteorites from differentiated parent bodies, and is therefore a maximum likely initial water content for any terrestrial planet in our solar system."4

A planet with Earth's mass and 1 to 3% by mass water in the mantle would produce a massive atmosphere.4

"Between 60 and 90% by mass of the original water in the planetary magma ocean is degassed into the growing atmosphere". "Even very small initial water contents, therefore, can produce substantial steam atmospheres."4

"When the surface temperature cools below the critical point (approximately 647 K [705.2 F] and 220 bars) the supercritical fluid and steam atmosphere will collapse into a surface ocean."4

"Within tens of millions of years of the initiation of a magma ocean the planetary mantle will be solid and compositionally stable, and the planet's surface temperature will have passed the critical point of water and cooled into the liquid water stability field."4

ATMOSPHERE

"When a giant impact occurs, atmosphere loss may occur due to global ground motion excited by a strong shock wave traveling in the planetary interior."8

"The estimated loss fraction for the giant impact is only 20%. Significant escape occurs only when the ground velocity is close to the escape velocity. Thus, most of the atmosphere should survive the giant impact."8

A small planet with an atmosphere can impact a larger planet. "A significant fraction of the impactor's atmosphere survives and is brought to the target planet."8