====== Examine planetary data ======
The planets of the Solar System show a wide range of interior structures, shaped by their size, composition, and thermal history. Based on spacecraft data, seismic studies (for Earth), gravitational measurements, and models, here is what we know:

==== Terrestrial Planets (Rocky) ====

^ Planet ^ Core ^ Mantle ^ Crust ^ Heat Sources ^ Activity Level ^
| **Mercury** | Large iron-rich core (∼85% of radius), partly liquid | Thin silicate mantle | Very thin crust | Initial accretion, some radioactive decay | Geologically inactive, ancient surface |
| **Venus** | Iron-nickel core (possibly liquid) | Thick silicate mantle | Volcanic crust | Radioactive decay | Still volcanically active, no plate tectonics |
| **Earth** | Solid inner core + liquid outer core | Convecting mantle | Oceanic & continental crust | Accretion, radioactive decay | Active tectonics, strong magnetic field |
| **Mars** | Large core (partly molten), mostly iron + sulfur | Stagnant mantle | Thick basaltic crust | Some radioactive heat | Geologically dead, but once active |

==== Gas Giants (Jupiter & Saturn) ====

^ Planet ^ Core ^ Interior Layers ^ Heat Sources ^ Activity Level ^
| **Jupiter** | Possibly a rocky/icy core (~10 Earth masses) | Metallic hydrogen layer + molecular hydrogen envelope | Accretional heat + slow contraction (Kelvin–Helmholtz mechanism) | Strong magnetic field, internal heat flux |
| **Saturn** | Small dense core | Similar to Jupiter, but less massive | Accretional + gravitational settling of helium | Emits more heat than it receives from the Sun |

==== Ice Giants (Uranus & Neptune) ====

^ Planet ^ Core ^ Mantle (Ices) ^ Atmosphere ^ Heat Sources ^ Activity Level ^
| **Uranus** | Rocky core | Water, ammonia, methane ices | Thin hydrogen–helium atmosphere | Low internal heat | Coldest planet, minimal activity |
| **Neptune** | Similar to Uranus, but possibly larger core | “Icy” mantle of volatiles | Similar atmosphere | More internal heat than Uranus | Strong winds, dynamic weather |

==== Dwarf Planets (e.g., Pluto) ====

  * Pluto likely has a rocky core and icy mantle.
  * May have or had a subsurface ocean.
  * Internal heating likely from radioactive decay.

==== Key Themes ====

  * **Size matters**: Larger planets retain heat longer and remain geologically active.
  * **Composition matters**: Rocky vs. gaseous vs. icy materials behave differently under pressure.
  * **Heat sources**: Gravitational accretion, radioactive decay, and slow contraction all contribute.
  * **Magnetic fields**: Produced by molten, convecting conductive layers (e.g., Earth’s outer core, Jupiter’s metallic hydrogen).

==== Final Note ====

The deeper interiors of many planets are still uncertain due to lack of direct data. Future missions (like seismometers on Mars or orbiters around Uranus/Neptune) may refine our understanding further.