How did the temperature structure of the solar nebula determine planetary composition?
The correct answer and explanation is :
The temperature structure of the solar nebula played a critical role in determining the composition of planets in the early solar system. The solar nebula was a rotating disk of gas and dust that surrounded the young Sun. As the nebula cooled, the temperature decreased with distance from the Sun, influencing the types of materials that could condense into solid bodies at various points in the disk.
Closer to the Sun, the temperature was high, around 1,300 K, which prevented the condensation of volatile compounds such as water, methane, and ammonia. Instead, only refractory (heat-resistant) materials like metals and silicates could condense to form solid particles. As a result, the inner solar system—closer to the Sun—was dominated by rocky, metal-rich planets such as Mercury, Venus, Earth, and Mars. These planets are composed primarily of heavy elements like iron, nickel, and silicates.
Further from the Sun, the temperature was much lower, dropping to around 100 K or less in the outer regions of the nebula. In this cooler zone, volatile compounds like water, methane, ammonia, and carbon dioxide could condense into ice. The outer planets—Jupiter, Saturn, Uranus, and Neptune—formed from a combination of ices, gases, and rock. These planets, known as gas giants and ice giants, have a significant proportion of lighter elements like hydrogen, helium, and ice, leading to their massive sizes and gaseous compositions.
In summary, the temperature gradient of the solar nebula determined the condensation points of different materials, which, in turn, influenced the composition of the planets. Rocky planets formed closer to the Sun where it was hotter, while gas and ice giants formed farther out where it was cooler, allowing for the presence of volatile substances. This temperature structure ultimately shaped the diversity of planetary compositions we see in the solar system today.