One question that has baffled planetary scientists is how oceans formed on the surface of terrestrial planets like Earth -- rocky planets made of silicate and metals.
一个困扰着行星科学家的问题是：海洋是怎样在像地球这样由硅酸盐和金属组成的石质行星的表面形成的？
OK, this is the Bohr model, Bohr model of the atom is planetary or nuclear.
好的，这就是波尔模型，波尔的原子模型是行星模型或者核心模型。
Within our own galaxy there are probably tens of thousands of planetary systems.
在我们所在的银河系中，很可能存在数以万计的行星系。
These disks are the remnants of planetary formation.
