冥王星大气层可能缺乏惰性气体
On the possible noble gas deficiency of Pluto's atmosphere
摘要：
我们使用的南极热力学模型来研究冥王星表面的形成和组成的贵气丰富的笼形物。通过考虑接近今天冥王星的大气成分和广泛的表面压力，我们发现Ar，Kr和H2O可以有效地被捕获在笼形物中，如果它们在表面形成，以类似于泰坦的方式。在冥王星上形成富含稀有气体的笼形物，可能会导致其大气丰度相对于其初始值大幅下降。如果这些惰性气体在冥王星早期的大气中是原太阳的比例，那么在冥王星上平均几厘米的笼形物厚度就足以捕获所有的Ar、Kr和Ar。由于在一段较长的时间（数百万年）的大气逃逸应导致惰性气体丰度，要么保持不变或随时间增加，我们发现，在大气中的Ar，Kr和H2O的潜在耗尽最好解释为它们捕获在笼形物中。一个关键的观测测试是测量Ar，因为新视野号航天器上的爱丽丝紫外光谱仪将足够灵敏，可以检测到比这里考虑的情况小10倍的丰度$\sim$。
英文摘要：
We use a statistical-thermodynamic model to investigate the formation and composition of noble-gas-rich clathrates on Pluto's surface. By considering an atmospheric composition close to that of today's Pluto and a broad range of surface pressures, we find that Ar, Kr and Xe can be efficiently trapped in clathrates if they formed at the surface, in a way similar to what has been proposed for Titan. The formation on Pluto of clathrates rich in noble gases could then induce a strong decrease in their atmospheric abundances relative to their initial values. A clathrate thickness of order of a few centimeters globally averaged on the planet is enough to trap all Ar, Kr and Xe if these noble gases were in protosolar proportions in Pluto's early atmosphere. Because atmospheric escape over an extended period of time (millions of years) should lead to a noble gas abundance that either remains constant or increases with time, we find that a potential depletion of Ar, Kr and Xe in the atmosphere would best be explained by their trapping in clathrates. A key observational test is the measurement of Ar since the Alice UV spectrometer aboard the New Horizons spacecraft will be sensitive enough to detect its abundance $\sim$10 times smaller than in the case considered here.
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