Answer:
D. planets forming atmospheres
Step-by-step explanation:
In space science, differentiation means the separation of or falling apart of the constituents of a planetary body as a result of the chemical and physical behavior. In this process, the heavenly body develops various layers where the denser material sinks into the planet's core while the lighter material forms the outer crust.
Thus all the options A, B and C are the result of the planetary differentiation process except option D.
Thus the answer is Option --
D. planets forming atmospheres