太阳星云中的冰线、星子成分和固体表面密度
Ice Lines, Planetesimal Composition and Solid Surface Density in the Solar Nebula
摘要：
到目前为止，还没有核心吸积模拟，可以成功地解释形成天王星或海王星在所观察到的2-3万年的寿命原行星盘。由于固体的吸积速率与可获得的星子表面密度成正比，加速行星形成的一种方法是全面考虑太阳星云中所有形成星子的固体。通过结合粘性演化的原恒星盘与冰形成的动力学模型，我们计算了太阳星云中的固体表面密度作为日心距离和时间的函数。我们发现了三种强烈有利于巨型行星形成的效应：（1）将质量从内太阳星云带到巨型行星形成区域的递减流，（2）最近的实验室结果（Collings et al. 2004）表明氨和水冰线应该重合，（3）在跨土星区域存在大量的甲烷冰。我们的结果表明，在整个跨土星区域，固体表面密度比Pollack等人（1996）的核心吸积模型中假设的要高3到4倍。我们还讨论了冰线的位置和它们在太阳星云中的运动，并从引力稳定性参数中提供了对可能的初始盘配置的新约束。
英文摘要：
To date, there is no core accretion simulation that can successfully account for the formation of Uranus or Neptune within the observed 2-3 Myr lifetimes of protoplanetary disks. Since solid accretion rate is directly proportional to the available planetesimal surface density, one way to speed up planet formation is to take a full accounting of all the planetesimal-forming solids present in the solar nebula. By combining a viscously evolving protostellar disk with a kinetic model of ice formation, we calculate the solid surface density in the solar nebula as a function of heliocentric distance and time. We find three effects that strongly favor giant planet formation: (1) a decretion flow that brings mass from the inner solar nebula to the giant planet-forming region, (2) recent lab results (Collings et al. 2004) showing that the ammonia and water ice lines should coincide, and (3) the presence of a substantial amount of methane ice in the trans-Saturnian region. Our results show higher solid surface densities than assumed in the core accretion models of Pollack et al. (1996) by a factor of 3 to 4 throughout the trans-Saturnian region. We also discuss the location of ice lines and their movement through the solar nebula, and provide new constraints on the possible initial disk configurations from gravitational stability arguments.
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