Replacement and late formation of atmospheric N2 on undifferentiated Titan by impacts
Replacement and late formation of atmospheric N2 on undifferentiated Titan by impacts
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DOI：
10.1038/npre.2011.5880.1
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发表时间：
2011-04
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影响因子：
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通讯作者：
Y. Sekine;H. Genda;S. Sugita;T. Kadono;T. Matsui
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作者：
Y. Sekine;H. Genda;S. Sugita;T. Kadono;T. Matsui
土星的卫星土卫六因其大量的氮气大气层而备受关注，但这种大气层的起源在很大程度上是未知的。行星和卫星上的大量次级大气层通常只有在吸积过程中的内部和化学反应发生实质性分化后才形成，然而泰坦的内部被发现是不完全分化的。在这里，我们提出，泰坦的氮大气层形成后吸积，从氨已经存在于泰坦在后期重轰炸期间约四十亿年前的转换。我们的激光枪实验表明，氨冰在撞击过程中非常有效地转化为N2。基于我们的实验结果的数值计算表明，土卫六将获得足够的N2来维持目前的大气，并且在后期重撞击之前存在的大部分大气将被撞击引起的N2所取代。我们的方案是能够产生一个富含N2的大气层与未分化的土卫六上的原始Ar很少。如果土卫六的大气层是由这种机制产生的，那么土卫六的N2来自太阳星云，与地球的N2来源不同，而土卫六和海卫一上的N2来源可能与冥王星上的N2来源根本不同。
Saturn’s moon Titan has attracted much attention because of its massive nitrogen atmosphere, but the origin of this atmosphere is largely unknown. Massive secondary atmospheres on planets and satellites usually form only after a substantial differentiation of the body’s interior and chemical reactions during accretion,,,,,, yet Titan’s interior has been found to be incompletely differentiated. Here we propose that Titan’s nitrogen atmosphere formed after accretion, by the conversion from ammonia that was already present on Titan during the period of late heavy bombardment about four billion years ago. Our laser-gun experiments show that ammonia ice converts to N2very efficiently during impacts. Numerical calculations based on our experimental results indicate that Titan would acquire sufficient N2to sustain the current atmosphere and that most of the atmosphere present before the late heavy bombardment would have been replaced by impact-induced N2. Our scenario is capable of generating a N2-rich atmosphere with little primordial Ar on undifferentiated Titan. If this mechanism generated Titan’s atmosphere, its N2was derived from a source in the solar nebula different from that for Earth, and the origins of N2on Titan and Triton may be fundamentally different from the origin of N2on Pluto.