What is the main difference between the inner and outer planets?
AInner planets are older; outer planets are younger
BInner planets are small and rocky; outer planets are large and made mostly of gas and ice
CInner planets are colder; outer planets are warmer
DInner planets have more moons than outer planets
The inner planets (Mercury, Venus, Earth, Mars) are small, dense, and composed of rock and metal. The outer planets (Jupiter, Saturn, Uranus, Neptune) are much larger, less dense, and composed primarily of hydrogen, helium, and ices. Jupiter alone has more mass than all the other planets combined. The outer planets also have far more moons and ring systems.
Question 2 Short Answer
Why are the inner planets rocky while the outer planets are gassy?
Think about your answer, then reveal below.
Model answer: In the early solar system, the area close to the young Sun was too hot for lightweight materials like ice and gas to condense — only rock and metal could survive, forming the inner planets. Farther from the Sun, temperatures were low enough for ices to form, creating larger cores that could attract and hold onto huge amounts of hydrogen and helium gas, building the gas giants.
The boundary where ice could first form is called the frost line (or snow line). It corresponds roughly to the current position of the asteroid belt. Inside the frost line, only rocky materials condensed from the solar nebula. Outside it, ices added significantly to the building material available, allowing much larger planets to form.
Question 3 True / False
Saturn would float in water because its density is less than water's density.
TTrue
FFalse
Answer: True
Saturn's average density is about 0.69 g/cm³, while water is 1.0 g/cm³. If you could find a bathtub large enough, Saturn would indeed float. This remarkably low density is because Saturn is composed mainly of hydrogen and helium gas, which are much less dense than the rock and metal that make up Earth and the other terrestrial planets.