Protoplanetary Propellers in Perturbed Accretion Disks.

在这个研究项目中，我们想扩展我们的散射-扩散模型，适用于行星环中的小卫星，在行星前盘中生长行星胚胎。尽管行星环和行星前盘有很大的不同，但它们共享一些基本的物理过程，证明了这种方法的合理性，并为该项目提供了基础。自从20世纪90年代中期发现太阳系外行星以来，行星形成理论获得了复兴。在离中心恒星非常近的地方发现类木行星，开启了对盘-行星相互作用和原行星相关迁移的研究。两类迁移行星被区分开来：大间隙诱导行星，以及无法清除圆盘间隙的小型原行星。这些类别让人想起行星环中的小卫星——比如土星的潘和达芙妮，它们会产生一个空的间隙，或者像我们的模型预测的那样，在行星环中雕刻出螺旋桨状的结构。事实上，卡西尼号航天器上的相机捕捉到了几百个螺旋桨，这些螺旋桨是由50……150米!此外，还发现了一个非常大的螺旋桨，指向一颗随机迁移的公里大小的小卫星。这两个圆盘的明显相似之处引发了一个问题：非间隙开放行星是否会在行星前圆盘中产生类似螺旋桨的结构？在什么情况下？这些行星会引起可观察到的垂直圆盘分层变化吗？什么过程可以打破螺旋桨状结构的对称性，从而导致行星迁移？一个吸积的行星胚胎对周围的盘状结构有什么影响？最后，土星环中有一颗迁移的小卫星这一事实为行星环是宇宙盘的天然动力学实验室提供了最终证据，也支持了扩展的散射-扩散模型对行星形成/迁移的可能重要性。

In this research project we want to extend our scattering-diffusion model, suitable for moonlets in planetary rings, to growing planetary embryos in preplanetary disks. Despite their large differences planetary rings and preplanetary disks share a few essential physical processes justifying this approach and providing the base for this project.Since the detection of extrasolar planets in the middle of the 90ties theories of planet formation have gained a renaissance. The detection of Jovian-like planets very close to the central star has initiated investigations of disk-planet interactions and related migration of protoplanets. Two classes of migrating planets are distinguished: laige gap-inducing planets, and alternatively, small protoplanets unable to clear a gap in the disk.These classes remind closely of moonlets in planetary rings - such as Saturn s Pan and Daphnis creating an empty gap or those carving propeller-like structures in planetary rings as predicted by our models. And indeed, the cameras on the Cassini spacecraft caught a few hundred propellers caused by moonlets with sizes of 50 ... 150 meters! Moreover, a very large propeller pointing to a kilometer-sized moonlet has been found which migrates stochastically.The obvious analogies in both disks provoke the questions: Do non-gap opening planets induce propeller-like structures in preplanetary disks? Under which conditions? Do these planets cause observable modifications of the vertical disk-stratification? What processes can break the symmetry of the propeller-like structures to cause planetary migration? What is the effect of an accreting planetary embryo on the surrounding disk-structure?And finally, the very fact of a migrating moonlet in Saturn s rings provides an ultimate proof for planetary rings being a natural dynamical lab for cosmic disks and also supports the possible importance of an extended scattering-diffusion model for planet formation/migration.