According to planet formation theory, there was a process of building that went on in the early solar system - smaller planetesimals to larger planetary embryos to actual planets.
根据行星形成理论，在太阳系早期，存在一个形成过程，更小的小行星形成稍大的行星胚胎，最终形成现在的行星。
Planetary embryos are thought of as bodies big enough to have undergone at least some internal melting, so that the interiors of these bodies have begun a process of forming layers.
行星胚胎被认为是足够大的物体，至少可以进行一些内部融合，于是，这些物体的内部就开始了形成层的过程。
The idea here is that - while Earth formed slowly from planetary embryos colliding - Mars is itself a solitary planetary embryo that formed very early in the history of our solar system.
这里想表达的观点是，当地球从行星胚胎间相互碰撞缓慢形成时，火星却是一个孤独的行星胚胎，在太阳系历史上形成得很早。
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