THERMAL EVOLUTION AND LIFETIME OF INTRINSIC MAGNETIC FIELDS OF SUPER-EARTHS IN HABITABLE ZONES
THERMAL EVOLUTION AND LIFETIME OF INTRINSIC MAGNETIC FIELDS OF SUPER-EARTHS IN HABITABLE ZONES
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DOI：
10.1088/0004-637x/726/2/70
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发表时间：
2010-10
期刊：
影响因子：
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通讯作者：
Chihiro Tachinami;H. Senshu;Shigeru Ida
中科院分区：
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作者：
Chihiro Tachinami;H. Senshu;Shigeru Ida
我们数值研究了不同质量类地行星在宜居带中的热演化，重点研究了发电机活动产生本征磁场的持续时间，这可能是影响行星宜居性的关键因素之一。特别是，我们对超级地球感到担忧，对它的观测正在迅速发展。我们用维奈状态方程、地幔粘性的Arrhenius公式和改进的地幔对流换热的天体物理混合长度理论计算了行星内部温度分布的演化。在用太阳系中的类地行星进行了定标后，我们将其应用于表面温度为300K(在宜居带内)和类地球成分的0.1M-10M⊕岩石行星。在核幔边界热流准则的基础上，根据计算的热演化结果估算了磁场的寿命。我们发现，寿命随行星质量(MP)缓慢增加，与初始温差无关(Δ)，但超过临界值Mc，p(∼O(1)M⊕)后，由于压力效应，地幔粘度增加，寿命急剧下降。我们导出了Mc，p作为ΔTCMB和一个流变学参数(活化体积，V*)的函数。因此，具有Mp>；Mp，c的超级地球的磁场寿命敏感地取决于反映行星吸积的ΔTcmb和在很高气压下具有不确定性的V*。需要更先进的高压实验和第一性原理模拟，以及行星吸积模拟，来讨论超级地球的宜居性。
We have numerically studied the thermal evolution of different-mass terrestrial planets in habitable zones, focusing on the duration of dynamo activity to generate their intrinsic magnetic fields, which may be one of the key factors in habitability of the planets. In particular, we are concerned with super-Earths, observations of which are rapidly developing. We calculated the evolution of temperature distributions in the planetary interior using Vinet equations of state, the Arrhenius-type formula for mantle viscosity, and the astrophysical mixing-length theory for convective heat transfer modified for mantle convection. After calibrating the model with terrestrial planets in the solar system, we apply it for 0.1–10 M⊕ rocky planets with a surface temperature of 300 K (in habitable zones) and Earth-like compositions. With the criterion of heat flux at the core–mantle boundary (CMB), the lifetime of the magnetic fields is evaluated from the calculated thermal evolution. We found that the lifetime slowly increases with planetary mass (Mp), independent of the initial temperature gap at the CMB (ΔTCMB), but beyond the critical value Mc,p (∼O(1) M⊕) it abruptly declines from the mantle viscosity enhancement due to the pressure effect. We derived Mc,p as a function of ΔTCMB and a rheological parameter (activation volume, V*). Thus, the magnetic field lifetime of super-Earths with Mp>Mp,c sensitively depends on ΔTCMB, which reflects planetary accretion, and V*, which has uncertainty at very high pressure. More advanced high-pressure experiments and first-principle simulation, as well as planetary accretion simulation, are needed to discuss the habitability of super-Earths.