GJ 1214 b上气层的三种可能成因
Three Possible Origins for the Gas Layer on GJ 1214b
摘要：
我们提出了一个分析的整体组成的MEarth过境的超级地球系外行星GJ 1214 b使用行星内部结构模型。我们认为GJ 1214 b上的气体层有三种可能的来源：来自原行星状星云的气体直接吸积、冰的升华和岩石物质的释气。仅凭对行星质量（M_p=6.55+/-0.98 M_{earth}）、半径（R_p=2.678+/-0.13 R_{earth}）和恒星辐射水平的测量，我们的主要结论是，我们无法推断出独特的组成。各种各样的行星内部符合测量的行星属性。尽管如此，GJ 1214 b相对较低的平均密度（rho_p=1870+/-400 kg m^{-3}）意味着它几乎肯定含有大量的气体成分。我们的第二个主要结论是，在大多数情况下，我们认为GJ 1214 b不会有液态水。即使外壳主要是升华的水冰，外壳也可能由夹在上面的蒸汽和下面更深处的等离子体（导电流体）之间的超流体层组成。在我们的模型中，GJ 1214 b上的水包层需要一个低的本征行星光度（<~ 2 TW）才能通过液相。
英文摘要：
We present an analysis of the bulk composition of the MEarth transiting super Earth exoplanet GJ 1214b using planet interior structure models. We consider three possible origins for the gas layer on GJ 1214b: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Armed only with measurements of the planet mass (M_p=6.55+/-0.98 M_{earth}), radius (R_p=2.678+/-0.13 R_{earth}), and stellar irradiation level, our main conclusion is that we cannot infer a unique composition. A diverse range of planet interiors fits the measured planet properties. Nonetheless, GJ 1214b's relatively low average density (rho_p=1870+/-400 kg m^{-3}) means that it almost certainly has a significant gas component. Our second major conclusion is that under most conditions we consider GJ 1214b would not have liquid water. Even if the outer envelope is predominantly sublimated water ice, the envelope will likely consist of a super-fluid layer sandwiched between vapor above and plasma (electrically conductive fluid) below at greater depths. In our models, a low intrinsic planet luminosity (<~2TW) is needed for a water envelope on GJ 1214b to pass through the liquid phase.
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