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arXiv 1106.4341astro-ph.EP
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地幔对流、Plate Tectonics和热外地球上的火山作用

Mantle Convection, Plate Tectonics, and Volcanism on Hot Exo-Earths

Joost van Summeren, Clinton P. Conrad, Eric Gaidos

摘要:

最近发现的靠近轨道的系外行星的地面温度应该在100到1000 K之间。它们很可能是潮汐锁定的,并且同步地围绕着它们的母星旋转,如果没有大气层,它们的昼夜表面的地面温度会相差几百到一千K。我们研究了地球质量行星的高地面温度和强地面温度对比度对(i)地幔对流模式,(ii)构造体制,(iii)部分熔融的速率和分布的影响,使用数值模拟的地幔对流与复合粘性/假塑性流变学。我们的模拟表明,如果一个接近的岩石系外行星缺乏大气层来重新分配热量,一个>~ 400 K的地面温度对比度可以维持一个不对称度1的地幔对流模式,其中行星的表面优先向寒冷的夜晚一侧的俯冲带移动。行星表面具有半球二分法,在夜晚一侧具有板块状构造,而在白天一侧具有持续发展的移动盖,具有弥漫的表面变形和活跃的火山活动。如果火山释气形成大气并重新分配热量,板块构造就会在全球范围内被弥漫性表面变形所取代,火山活动就会加速并在行星表面变得更加均匀地分布。

英文摘要:

Recently discovered exoplanets on close-in orbits should have surface temperatures of 100's to 1000's of K. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many 100's to 1000's K between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (i) pattern of mantle convection, (ii) tectonic regime, and (iii) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate that, if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a >~ 400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dichotomy, with plate-like tectonics on the night side and a continuously evolving mobile lid day side with diffuse surface deformation and vigorous volcanism. If volcanic outgassing establishes an atmosphere and redistributes heat, plate tectonics is globally replaced by diffuse surface deformation and volcanism accelerates and becomes distributed more uniformly across the planetary surface.

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