Earth,which is mostly rock and iron,has a density of 5515 kg/m³.Ganymede,Jupiter's largest satellite,contains much water and water ice and has a density of 1940 kg/m³.Io has a density of 3570 kg/m³.What conclusions have astronomers drawn from this?
A) Io must be composed of some new material other than rocks, iron, water, or ice.
B) Io is composed of compressed water and water ice.
C) Io is mostly rock and iron, but because of its smaller mass, it cannot compress the material as much as Earth can.
D) Since Io is smaller than Earth, it is expected to have a smaller density regardless of composition.

Question

Quizplus · Accepted Answer

The density of a planet or moon depends on its composition and mass. Io has a lower density than Earth because it is smaller in mass and cannot compress the rock and iron as much as Earth can. This means that Io is mostly rock and iron, like Earth, but it has a lower density than Earth because of its smaller size. Option A and B are not correct because Io is not composed of new material or compressed water and water ice. Option D is partially correct but does not explain why Io has a lower density.

Earth,which Is Mostly Rock and Iron,has a Density of 5515