首页> 外文期刊>Astrobiology >Coronal Mass Ejection (CME) Activity of Low Mass M Stars as an Important Factor for the Habitability of Terrestrial Exoplanets. Ⅱ. CME-Induced Ion Pick Up of Earth-Like Exoplanets in Close-In Habitable Zones
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Coronal Mass Ejection (CME) Activity of Low Mass M Stars as an Important Factor for the Habitability of Terrestrial Exoplanets. Ⅱ. CME-Induced Ion Pick Up of Earth-Like Exoplanets in Close-In Habitable Zones

机译:低质量M星的冠状物质抛射(CME)活动是地球系外行星宜居性的重要因素。 Ⅱ。 CME诱导的离子在近郊宜居区中的系外行星的拾取。

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Atmospheric erosion of CO_2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wavelengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ioniza-tion processes due to exothermic chemical reactions and cooling by the CO_2 infrared radiation in the 15 μm band. Our study shows that intense XUV radiation of active M stars results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O~+ ion pick up at orbital distances ≤ 0.2 astronomical units. We have found that, when exposed to intense XUV fluxes, atmospheres with CO_2/N_2 mixing ratios lower than 96% will show an increase in exospheric temperatures and expanded thermosphere-exosphere environments. Hence, they suffer stronger atmospheric erosion, which can result in the total loss of several hundred bars even if an exoplanet is protected by a "magnetic shield" with its boundary located at 1 Earth radius above the surface. Furthermore, our study indicates that magnetic moments of tidally locked Earth-like exoplanets are essential for protecting their expanded upper atmospheres because of intense XUV radiation against CME plasma erosion. Therefore, we suggest that larger and more massive terrestrial-type exoplanets may better protect their atmospheres against CMEs, because the larger cores of such exoplanets would generate stronger magnetic moments and their higher gravitational acceleration would constrain the expansion of their thermosphere-exosphere regions and reduce atmospheric escape.
机译:研究了由冕状物质抛射(CME)诱导的活跃M型矮星宜居区域附近的离子吸收引起的富含CO_2的地球大小系外行星的大气侵蚀。由于M星在X射线和极紫外辐射(XUV)波长上长期处于活动状态,因此我们在各种XUV通量输入值上应用了热平衡模型,以通过光解离和电离过程模拟热球加热。通过15μm波段的CO_2红外辐射放热化学反应并冷却。我们的研究表明,活跃的M恒星强烈的XUV辐射会导致大气膨胀和扩展的大气圈。使用针对各种XUV通量计算出的热层中性和离子密度,我们应用了数值测试粒子模型来模拟由于其与预期的最小和最大CME等离子体流之间的相互作用而引起的扩展的外层大气中的离子吸收损失。我们的结果表明,没有或微弱的磁矩的类地球系外行星可能会由于CME诱导的O〜+离子在轨道距离≤上消失而损失数十至数百个大气压,甚至损失整个大气层。 0.2天文单位。我们发现,当暴露于强烈的XUV通量时,CO_2 / N_2混合比低于96%的大气将显示出大气圈温度的升高和热圈-大气圈环境的扩大。因此,它们遭受更强的大气侵蚀,即使系外行星受到边界位于表面上方1个地球半径处的“电磁屏蔽”保护,也可能导致数百巴的总损失。此外,我们的研究表明,潮汐锁定的类地球系外行星的磁矩对于保护其扩展的高层大气至关重要,因为强烈的XUV辐射可抵抗CME等离子体侵蚀。因此,我们建议更大和更大质量的地球系系外行星可能更好地保护其大气免受CME影响,因为此类系外行星的较大核心将产生更强的磁矩,而其更高的重力加速度将限制其热圈-外层区域的膨胀并减少大气逃逸。

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