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Difficulty: HardThe Solar System and Planets

Planets in the Solar System are broadly divided into terrestrial and Jovian groups based on their formation history, physical composition, and bulk density. Which of the following statements correctly distinguishes the bulk composition and structural characteristics of terrestrial planets from Jovian planets?

  1. A
    Terrestrial planets have low bulk densities because of porous silicate crusts, whereas Jovian planets exhibit high bulk densities due to extreme gravitational compression throughout their volumes.
  2. B
    Terrestrial planets consist primarily of volatile ices surrounding small metallic cores, whereas Jovian planets consist entirely of uniform gaseous mixtures with no distinct inner core boundaries.
  3. Terrestrial planets possess high bulk densities with solid rocky mantles and metallic cores surrounded by shallow atmospheres, whereas Jovian planets possess low bulk densities with massive gaseous or fluid envelopes surrounding dense cores.Answer
  4. D
    Terrestrial planets retain thick primordial hydrogen-helium atmospheres due to high surface gravity, whereas Jovian planets have lost their lighter gases over time through solar wind stripping.

Answer

Terrestrial planets possess high bulk densities with solid rocky mantles and metallic cores surrounded by shallow atmospheres, whereas Jovian planets possess low bulk densities with massive gaseous or fluid envelopes surrounding dense cores.
The statement describing terrestrial planets as having high bulk densities with solid rocky mantles and metallic cores, and Jovian planets as having low bulk densities with massive gaseous/fluid envelopes, accurately reflects the structural and compositional divergence across the frost line.

Step-by-Step Solution

1
Analyze the compositional origins of inner versus outer planets relative to the solar frost line.
Inner terrestrial planets condensed from refractory materials (metals and silicates), while outer Jovian planets accumulated large amounts of volatile gases and ices beyond the frost line.
Temperature gradients in the protoplanetary disk determined what compounds could condense into planetesimals.
2
Compare bulk density and internal structure between the two groups.
Terrestrial bodies have high bulk densities (3.9–5.5 g/cm33.9\text{--}5.5\text{ g/cm}^3) with solid metallic cores and silicate crusts; Jovian bodies have low bulk densities (0.7–1.6 g/cm30.7\text{--}1.6\text{ g/cm}^3) dominated by thick gaseous/fluid layers.
Dense rock and iron yield higher average density than light hydrogen, helium, water, ammonia, and methane.
3
Evaluate atmospheric retention characteristics.
Jovian planets have sufficient gravitational mass to retain primordial hydrogen and helium, whereas terrestrial atmospheres are shallow, secondary outgassed or captured envelopes.
Escape velocity and planetary surface temperatures determine which gas molecules can be gravitationally bound over billions of years.

Key Concept

Planetary Classification and Structural Differentiation
Estimated Time:1m 30s
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Topics

The Solar System and Planets

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