(i) Why are the terrestrial planets rocky?
Answers
Explanation:
A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars.
The temperature of the early solar system explains why the inner planets are rocky and the outer ones are gaseous. As the gases coalesced to form a protosun, the temperature in the solar system rose. In the inner solar system temperatures were as high as 2000 K, while in the outer solar system it was as cool as 50 K. In the inner solar system, only substances with very high melting points would have remained solid. All the rest would have vaoprized. So the inner solar system objects are made of iron, silicon, magnesium, sulfer, aluminum, calcium and nickel. The inner planets are much smaller than the outer planets and because of this have relatively low gravity and were not able to attract large amounts of gas to their atmospheres. In the outer regions of the solar system where it was cooler, other elements like water and methane did not vaporize and were able to form the giant planets. These planets were more massive than the inner planets and were able to attract large amounts of hydrogen and helium, which is why they are composed mainly of hydrogen and helium, the most abundant elements in the solar system, and in the universe.