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arXiv 1104.4977astro-ph.EP
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彗星动力学和化学模型对天王星和海王星形成位置的约束

On the formation location of Uranus and Neptune as constrained by dynamical and chemical models of comets

Jj Kavelaars, Olivier Mousis, Jean-Marc Petit, Harold A. Weaver

摘要:

在土星的卫星土卫二中观测到的D/H富集与在近各向同性彗星中观测到的值非常相似。由于预测的强烈变化的D/H与日心距离的太阳星云,这一观察联系的原始源区的近各向同性彗星的形成位置的土卫二。也就是说,来自近各向同性类的彗星最有可能是从土卫二形成位置附近的源区进入它们目前的水库奥尔特云的。对奥尔特云形成的动力学模拟表明,天王星和海王星主要负责向奥尔特云输送物质。此外,土卫二是由土星捕获其气体包层的位置附近的太阳星云凝聚而成的,很可能就在土星目前在太阳系的位置或附近。这些证据的结合似乎要求天王星和海王星在奥尔特云形成的时期比现在更接近土星的当前位置。这样的配置与外太阳系演化的尼斯模型是一致的。进一步测量彗星,特别是黄道彗星的D/H丰度,将为各种外太阳系形成模型提供一个很好的解释。

英文摘要:

The D/H enrichment observed in Saturn's satellite Enceladus is remarkably similar to the values observed in the nearly-isotropic comets. Given the predicted strong variation of D/H with heliocentric distance in the solar nebula, this observation links the primordial source region of the nearly-isotropic comets with the formation location of Enceladus. That is, comets from the nearly-isotropic class were most likely fed into their current reservoir, the Oort cloud, from a source region near the formation location of Enceladus. Dynamical simulations of the formation of the Oort cloud indicate that Uranus and Neptune are, primarily, responsible for the delivery of material into the Oort cloud. In addition, Enceladus formed from material that condensed from the solar nebula near the location at which Saturn captured its gas envelope, most likely at or near Saturn's current location in the solar system. The coupling of these lines of evidence appears to require that Uranus and Neptune were, during the epoch of the formation of the Oort cloud, much closer to the current location of Saturn than they are currently. Such a configuration is consistent with the Nice model of the evolution of the outer solar system. Further measurements of the D/H enrichment in comets, particularly in ecliptic comets, will provide an excellent discriminator among various models of the formation of the outer solar system.

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