Formation of early water oceans on rocky planets
Formation of early water oceans on rocky planets
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DOI：
10.1007/s10509-010-0535-3
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发表时间：
2011-04-01
影响因子：
1.9
通讯作者：
Elkins-Tanton, Linda T.
中科院分区：
文献类型：
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作者：
Elkins-Tanton, Linda T.
类地行星具有硅酸盐地幔和金属内核，在吸积过程中可能会获得水和碳化合物。在这里，我研究了允许早期形成地表水海洋的条件（与此同时，冷却到恶劣的地表条件），以及将行星内部气体脱入大气的时间轴。在岩浆海洋凝固结束时，行星初始挥发性预算的大部分被脱气到大气中，只有一小部分原始挥发物通过后来的火山活动释放到大气中。在岩石行星的大块地幔中有水的吸积，它们产生早期海洋的机制有两种：第一，如果它们的大块成分中至少有1 - 3%的水，那么在岩浆海洋凝固结束时，液态水可能会被挤出行星表面。第二，在初始含水量低至0.01质量%或更低的情况下，在凝固过程中产生大量超临界流体和蒸汽气氛，冷却后坍塌成水海洋。这一过程所需的低含水量表明，岩石超级地球系外行星可能会在它们最后一次主要的吸积撞击后的数千万到数亿年里，通过大气层的坍塌，产生水海洋。
Terrestrial planets, with silicate mantles and metallic cores, are likely to obtain water and carbon compounds during accretion. Here I examine the conditions that allow early formation of a surface water ocean (simultaneous with cooling to clement surface conditions), and the timeline of degassing the planetary interior into the atmosphere. The greatest fraction of a planet's initial volatile budget is 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 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 mass% or lower, during solidification a massive supercritical fluid and steam atmosphere is produced that collapses into a water ocean upon cooling. The low water contents required for this process indicate that rocky super-Earth exoplanets may be expected to commonly produce water oceans within tens to hundreds of millions of years of their last major accretionary impact, through collapse of their atmosphere.