Beginning in the 1940s, astronomers returned to the idea of the solar nebula to create a modification of it called the condensation theory.
There were critics of the nebular theory in the nineteenth century, among them James Clerk Maxwell, who had figured out the fundamentals of electromagnetic radiation. What Maxwell and the other critics of the Kant-Laplace theory didn't know about was interstellar dust. Microscopic dust grains—ice crystals and rocky matter— formed in the cooling atmosphere of dying stars, then grew by attracting additional atoms and molecules of various gases. These dust grains served two purposes in the formation of planets:
1. The presence of grains hastened the collapse of the nebular cloud by promoting the radiation of heat from it. This radiation of heat cooled the cloud, accelerating its collapse.
2. Each grain acted as a condensation nucleus, like the grain of sand in an oyster that eventually becomes a pearl. These grains eventually grew into pearls the size of worlds. In effect, these grains were planetary seeds.
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