Final answer:
The chemical composition of planets is determined by the condensation temperature of materials and their distance from the Sun during formation. Materials like metals and silicates formed closer to the Sun, while ices and organics formed further away. The giant planets' composition mirrors that of the Sun, while terrestrial planets are made up of heavier elements.
Step-by-step explanation:
Chemical Composition of Planets and Solar Nebula
The chemical composition of a planet in our solar system largely depends on the condensation temperature of materials in the solar nebula and their proximity to the Sun during the formation process. According to the solar nebula theory, the solar system formed about 4.5 billion years ago from a rotating cloud of vapor and dust. As this nebula collapsed due to gravity, it created a disk with varying temperatures; metals and rock-forming silicates condensed first in the high-temperature regions close to the Sun. Farther out, where it was cooler, sulfur compounds, carbon- and water-rich silicates, and eventually ices and organic compounds could solidify. The temperature and distance from the Sun dictated which materials became part of the different planets being formed.
The giant planets, like Jupiter and Saturn, were able to attract and hold on to the hydrogen-rich gases similar to those found in the Sun, giving them a 'cosmic' composition. However, Uranus and Neptune captured much less of these gases, resulting in a different makeup more heavily influenced by their icy and rocky cores. Over time, the solar wind from the young Sun eventually cleared away lighter gases, marking the end of the initial formation period.
This chemical differentiation is evidenced by the planetary composition we observe today, where terrestrial planets lack the abundance of light gases and ices that characterize the outer planets. Spectroscopic analysis reveals a dominance of heavier elements like iron and silicon in the inner planets, indicating that they formed in regions too hot for lighter materials to condense, or such materials were lost during the formation.