What accounts for the large density differences between the terrestrial and Jovian planets?
The correct answer and explanation is :
The large density differences between terrestrial and Jovian planets are primarily due to their composition and formation history.
Correct Answer:
Terrestrial planets (Mercury, Venus, Earth, and Mars) are composed primarily of rock and metal, which are dense materials. In contrast, Jovian planets (Jupiter, Saturn, Uranus, and Neptune) consist mostly of hydrogen, helium, and ices, which are much less dense.
Explanation:
The differences in density between terrestrial and Jovian planets stem from how they formed and the materials available in their respective regions of the solar system.
- Composition Differences:
- Terrestrial planets formed closer to the Sun, where the solar heat prevented light gases like hydrogen and helium from condensing. Instead, only dense materials like iron, nickel, and silicates (rocky minerals) could solidify, leading to a high density (around 3.9 to 5.5 g/cm³).
- Jovian planets formed in the colder outer regions of the solar system, where ices (water, methane, and ammonia) could condense. These planets also captured large amounts of hydrogen and helium, which are the lightest elements, resulting in a much lower overall density (around 0.7 to 1.6 g/cm³).
- Formation Process (Nebular Hypothesis):
- In the early solar system, the Sun’s radiation pushed lighter gases outward. The inner planets formed from heavy materials that could withstand the heat.
- Farther from the Sun, temperatures were low enough for volatile compounds (water, methane, ammonia) to condense, allowing Jovian planets to form with massive gaseous envelopes around a small core.
- Gravitational Effects:
- Despite their enormous size, Jovian planets have low densities because their large volumes are composed mainly of light gases.
- Saturn, for example, has a density (0.69 g/cm³) lower than water, meaning it could float in a hypothetical massive ocean.
Thus, the key reason for the density differences is the varying composition of planets due to temperature variations in the early solar system and their ability to capture light gases.