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arXiv 1709.04736astro-ph.EP
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迷你海王星的形成

The formation of mini-Neptunes

Julia Venturini, Ravit Helled

摘要:

小海王星似乎是常见的行星。在这项工作中,我们调查可能的形成历史和预测的发生率的迷你海王星假设行星的形式超越了冰线。我们认为卵石和星子吸积占信封富集和两个不同的不透明度条件。我们发现,当包括挥发物的包层富集时,迷你海王星的形成是一个相对频繁的输出,并且存在一个相对较低的固体吸积速率(每年约10^{-6}个地球质量)的迷你海王星形成的“最佳点”。这个速率对于低/中等质量的原行星盘和/或低金属丰度的盘是典型的。随着卵石的吸积,包层富集和高不透明度有利于迷你海王星的形成,在大的半长轴(~30 AU)和低盘粘度下更有效地形成。对于星子吸积,这样的行星也可以在没有富集的情况下形成,不透明度是生长历史和有利形成位置的关键方面。最后,我们表明,海王星类行星的形成仍然是一个挑战的行星形成理论。

英文摘要:

Mini-Neptunes seem to be common planets. In this work we investigate the possible formation histories and predicted occurrence rates of mini-Neptunes assuming the planets form beyond the iceline. We consider pebble and planetesimal accretion accounting for envelope enrichment and two different opacity conditions. We find that the formation of mini-Neptunes is a relatively frequent output when envelope enrichment by volatiles is included, and that there is a "sweet spot" for mini-Neptune formation with a relatively low solid accretion rate of ~10^{-6} Earth masses per year. This rate is typical for low/intermediate-mass protoplanetary disks and/or disks with low metallicities. With pebble accretion, envelope enrichment and high opacity favor the formation of mini-Neptunes, with more efficient formation at large semi-major axes (~30 AU) and low disk viscosity. For planetesimal accretion, such planets can form also without enrichment, with the opacity being a key aspect in the growth history and favorable formation location. Finally, we show that the formation of Neptune-like planets remains a challenge for planet formation theories.

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