* Composition: Terrestrial planets are primarily composed of rock and metals, elements that remain solid even at relatively high temperatures.
* Frost Line: The frost line is the distance from the star where it's cold enough for volatile compounds like water, methane, and ammonia to freeze. Beyond this line, these ices can readily condense and become part of planetesimals.
* Planetesimal Formation: Within the frost line, planetesimals (the building blocks of planets) primarily formed from rocky and metallic materials. These planetesimals then accreted through collisions and gravity, eventually forming terrestrial planets.
In summary: The inner region of the solar nebula, closer to the star and within the frost line, provided the right conditions for rocky planetesimals to form and coalesce into terrestrial planets like Mercury, Venus, Earth, and Mars.
