Correct Answer:
B. Earth
The correct answer is Earth. Among all the planets in our Solar System, Earth is the densest, with an average density of approximately 5.51 grams per cubic centimeter. This is significantly higher than any of the other terrestrial or giant planets.
Why Earth is the Densest Planet
- Massive Iron Core: Earth's high density is primarily due to its large, heavy metallic core, composed mainly of iron and nickel. The immense pressure from the overlying layers compresses the core to a density greater than that of pure iron at the surface.
- Comparison with Mercury: Mercury is the second densest planet (about 5.43 g/cm³). Despite having a proportionally huge iron core, its much smaller size means gravitational compression is weaker, keeping its overall density slightly below Earth's.
- Venus and Mars: Venus has a similar size and composition to Earth, but its internal structure yields a density of roughly 5.24 g/cm³. Mars has a thinner, less compressed mantle and a smaller core, resulting in a density of only about 3.93 g/cm³.
- Giant Planets: The gas giants (Jupiter, Saturn) and ice giants (Uranus, Neptune) are composed predominantly of lighter elements like hydrogen and helium, making their densities far lower (e.g., Saturn could theoretically float in water).
Hence, Earth is the planet with the highest average density.